normal physiology. Lecture notes: briefly, the most important

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normal physiology. Lecture notes: briefly, the most important

Lecture notes, cheat sheets

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Table of contents

Introduction to normal physiology
Physiological properties and features of the functioning of excitable tissues (Physiological characteristics of excitable tissues. Laws of irritation of excitable tissues. The concept of the state of rest and activity of excitable tissues. Physico-chemical mechanisms of the emergence of the resting potential. Physico-chemical mechanisms of the emergence of the action potential)
Physiological properties of nerves and nerve fibers (Physiology of nerves and nerve fibers. Types of nerve fibers. Mechanisms for conducting excitation along a nerve fiber. Laws for conducting excitation along a nerve fiber)
Muscle physiology (Physical and physiological properties of skeletal, cardiac and smooth muscles. Mechanisms of muscle contraction)
Physiology of synapses (Physiological properties of synapses, their classification. Mechanisms of excitation transmission in synapses using the example of the myoneural synapse. Physiology of mediators. Classification and characteristics)
Physiology of the central nervous system (Basic principles of the functioning of the central nervous system. Structure, functions, methods of studying the central nervous system. Neuron. Structural features, meaning, types. Reflex arc, its components, types, functions. Functional systems of the body. Coordination activity of the central nervous system. Types of inhibition, interaction of processes excitation and inhibition in the central nervous system. Experience of I. M. Sechenov. Methods for studying the central nervous system)
Physiology of various sections of the central nervous system (Physiology of the spinal cord. Physiology of the hindbrain and midbrain. Physiology of the diencephalon. Physiology of the reticular formation and limbic system. Physiology of the cerebral cortex)
Physiology of the autonomic nervous system (Anatomical and physiological features of the autonomic nervous system. Functions of the sympathetic, parasympathetic and methsympathetic types of the nervous system)
Physiology of the endocrine system. The concept of endocrine glands and hormones, their classification (General ideas about endocrine glands. Properties of hormones, their mechanism of action. Synthesis, secretion and release of hormones from the body. Regulation of the activity of endocrine glands)
Characteristics of individual hormones (Hormones of the anterior lobe of the pituitary gland. Hormones of the middle and posterior lobes of the pituitary gland. Hormones of the pineal gland, thymus, parathyroid glands. Hormones of the thyroid gland. Iodinated hormones. Thyroid calcitonin. Dysfunction of the thyroid gland. Hormones of the pancreas. Dysfunction of the pancreas. Adrenal hormones. Glucocorticoids. Adrenal hormones. Mineralocorticoids. Sex hormones. Hormones of the adrenal medulla. Sex hormones. Menstrual cycle. Placental hormones. The concept of tissue hormones and antihormones)
Higher nervous activity (The concept of higher and lower nervous activity. The formation of conditioned reflexes. Inhibition of conditioned reflexes. The concept of a dynamic stereotype. The concept of types of nervous system. The concept of signal systems. Stages of formation of signal systems)
Physiology of the heart (Components of the circulatory system. Circulation circles. Morphofunctional features of the heart. Physiology of the myocardium. Conducting system of the myocardium. Properties of atypical myocardium. Automaticity of the heart. Energy supply of the myocardium. Coronary blood flow, its features. Reflex influences on the activity of the heart. Nervous regulation of the activity of the heart. Humoral regulation of heart activity. Vascular tone and its regulation. Functional system that maintains blood pressure at a constant level. Histohematic barrier and its physiological role)
Physiology of respiration. Mechanisms of external respiration (The essence and significance of breathing processes. External respiration apparatus. The meaning of components. The mechanism of inhalation and exhalation. The concept of breathing pattern)
Physiology of the respiratory center (Physiological characteristics of the respiratory center. Humoral regulation of neurons of the respiratory center. Nervous regulation of the activity of neurons of the respiratory center)
Physiology of blood (Homeostasis. Biological constants. The concept of the blood system, its functions and significance. Physico-chemical properties of blood)
Physiology of blood components (Blood plasma, its composition. Physiology of red blood cells. Types of hemoglobin and its significance. Physiology of leukocytes. Physiology of platelets)
Physiology of blood. Blood immunology (Immunological basis for determining blood group. Antigenic system of erythrocytes, immune conflict)
Physiology of hemostasis (Structural components of hemostasis. Mechanisms of platelet and coagulation thrombus formation. Blood coagulation factors. Blood coagulation phases. Physiology of fibrinolysis)
Physiology of the kidneys (Functions, significance of the urinary system. Structure of the nephron. Mechanism of tubular reabsorption)
Physiology of the digestive system (Concept of the digestive system. Its functions. Types of digestion. Secretory function of the digestive system. Motor activity of the gastrointestinal tract. Regulation of motor activity of the gastrointestinal tract. The mechanism of sphincters. Physiology of absorption. The mechanism of absorption of water and minerals. Mechanisms absorption of carbohydrates, fats and proteins. Mechanisms for regulating absorption processes. Physiology of the digestive center. Physiology of hunger, appetite, thirst, satiety)

LECTURE No. 1. Introduction to normal physiology

Normal physiology - biological discipline that studies:

1) the functions of the whole organism and individual physiological systems (for example, cardiovascular, respiratory);

2) the functions of individual cells and cellular structures that make up organs and tissues (for example, the role of myocytes and myofibrils in the mechanism of muscle contraction);

3) interaction between individual organs of individual physiological systems (for example, the formation of erythrocytes in the red bone marrow);

4) regulation of the activity of internal organs and physiological systems of the body (for example, nervous and humoral).

Physiology is an experimental science. It distinguishes two methods of research - experience and observation. Observation - the study of the behavior of an animal under certain conditions, usually over a long period of time. This makes it possible to describe any function of the body, but makes it difficult to explain the mechanisms of its occurrence. The experience is acute and chronic. The acute experiment is carried out only for a short time, and the animal is in a state of anesthesia. Due to the large blood loss, there is practically no objectivity. The chronic experiment was first introduced by I. P. Pavlov, who proposed to operate on animals (for example, fistula on the stomach of a dog).

A large section of science is devoted to the study of functional and physiological systems. Physiological system - This is a constant collection of various organs, united by some common function. The formation of such complexes in the body depends on three factors:

1) metabolism;

2) energy exchange;

3) exchange of information.

Functional system - a temporary set of organs that belong to different anatomical and physiological structures, but provide the performance of special forms of physiological activity and certain functions. It has a number of properties such as:

1) self-regulation;

2) dynamism (disintegrates only after the desired result is achieved);

3) the presence of feedback.

Due to the presence of such systems in the body, it can work as a whole.

A special place in normal physiology is given to homeostasis. Homeostasis - a set of biological reactions that ensure the constancy of the internal environment of the body. It is a liquid medium, which is composed of blood, lymph, cerebrospinal fluid, tissue fluid. Their averages support the physiological norm (for example, blood pH, blood pressure, hemoglobin, etc.).

So, normal physiology is a science that determines the vital parameters of the body, which are widely used in medical practice.

LECTURE No. 2. Physiological properties and features of the functioning of excitable tissues

1. Physiological characteristics of excitable tissues

The main property of any fabric is irritability, i.e., the ability of a tissue to change its physiological properties and exhibit functional functions in response to the action of stimuli.

Irritants are factors of the external or internal environment that act on excitable structures.

There are two groups of irritants:

1) natural (nerve impulses that occur in nerve cells and various receptors);

2) artificial: physical (mechanical - shock, injection; temperature - heat, cold; electric current - alternating or direct), chemical (acids, bases, esters, etc.), physicochemical (osmotic - sodium chloride crystal) .

Classification of stimuli according to the biological principle:

1) adequate, which, with minimal energy costs, cause tissue excitation in the natural conditions of the organism's existence;

2) inadequate, which cause excitation in the tissues with sufficient strength and prolonged exposure.

The general physiological properties of tissues include:

1) excitability - the ability of living tissue to respond to the action of a sufficiently strong, fast and long-acting stimulus by changing physiological properties and the emergence of an excitation process.

The measure of excitability is the threshold of irritation. Irritation threshold - this is the minimum strength of the stimulus, which for the first time causes visible responses. Since the threshold of irritation also characterizes excitability, it can also be called the threshold of excitability. Irritation of lesser intensity, which does not cause responses, is called subthreshold;

2) conductivity - the ability of the tissue to transmit the resulting excitation due to the electrical signal from the site of irritation along the length of the excitable tissue;

3) refractoriness - a temporary decrease in excitability simultaneously with the excitation that has arisen in the tissue. Refractoriness is absolute (no response to any stimulus) and relative (excitability is restored, and the tissue responds to a subthreshold or suprathreshold stimulus);

4) lability - the ability of excitable tissue to respond to irritation at a certain speed. Lability is characterized by the maximum number of excitation waves that occur in the tissue per unit time (1 s) in exact accordance with the rhythm of the applied stimuli without the phenomenon of transformation.

2. Laws of irritation of excitable tissues

The laws establish the dependence of the tissue response on the parameters of the stimulus. This dependence is typical for highly organized tissues. There are three laws of irritation of excitable tissues:

1) the law of the strength of irritation;

2) the law of duration of irritation;

3) the excitation gradient law.

Law force of irritation establishes the dependence of the response on the strength of the stimulus. This dependence is not the same for individual cells and for the whole tissue. For single cells, the dependence is called "all or nothing". The nature of the response depends on the sufficient threshold value of the stimulus. When exposed to a subthreshold value of stimulation, no response will occur (nothing). When stimulation reaches a threshold value, a response occurs; it will be the same under the action of a threshold and any superthreshold value of the stimulus (all part of the law).

For a set of cells (for a tissue), this dependence is different, the response of the tissue is directly proportional to a certain limit to the strength of the applied irritation. The increase in the response is due to the fact that the number of structures involved in the response increases.

Law duration of irritations. The tissue response depends on the duration of the stimulation, but is carried out within certain limits and is directly proportional. There is a relationship between the strength of stimulation and the duration of its action. This dependence is expressed as a curve of force and time. This curve is called the Goorweg-Weiss-Lapic curve. The curve shows that no matter how strong the stimulus is, it must act for a certain period of time. If the time interval is small, then the response does not occur. If the stimulus is weak, then no matter how long it acts, no response occurs. The strength of the stimulus gradually increases, and at a certain moment a tissue response occurs. This force reaches a threshold value and is called rheobase (the minimum force of irritation that causes a primary response). The time during which a current equal to the rheobase acts is called useful time.

Law irritation gradient. Gradient - this is the steepness of the increase in irritation. The tissue response depends to a certain extent on the gradient of stimulation. With a strong stimulus, about the third time the stimulus is applied, the response occurs faster, since it has a stronger gradient. If you gradually increase the threshold of irritation, then the phenomenon of accommodation occurs in the tissue. Accommodation is the adaptation of tissue to a stimulus that slowly increases in strength. This phenomenon is associated with the rapid development of Na channel inactivation. The irritation threshold gradually increases, and the stimulus always remains subthreshold, i.e., the irritation threshold increases.

The laws of irritation of excitable tissues explain the dependence of the response on the parameters of the stimulus and ensure the adaptation of organisms to the factors of the external and internal environment.

3. The concept of the state of rest and activity of excitable tissues

About the state of rest in excitable tissues, they say in the case when the tissue is not affected by an irritant from the external or internal environment. At the same time, a relatively constant level of metabolism is observed, there is no visible functional tissue administration. The state of activity is observed in the case when an irritant acts on the tissue, while the metabolic level changes, and the functional administration of the tissue is observed.

The main forms of the active state of excitable tissue are excitation and inhibition.

Excitation - this is an active physiological process that occurs in the tissue under the influence of an irritant, while the physiological properties of the tissue change, and the functional administration of the tissue is observed. Excitation is characterized by a number of signs:

1) specific features characteristic of a particular type of tissue;

2) non-specific features characteristic of all types of tissues (the permeability of cell membranes, the ratio of ion flows, the charge of the cell membrane change, an action potential arises that changes the level of metabolism, oxygen consumption increases and carbon dioxide emission increases).

According to the nature of the electrical response, there are two forms of excitation:

1) local, non-propagating excitation (local response). It is characterized by:

a) there is no latent period of excitation;

b) occurs under the action of any stimulus, i.e. there is no threshold of irritation, it has a gradual character;

c) there is no refractoriness, that is, in the process of the onset of excitation, the excitability of the tissue increases;

d) attenuates in space and spreads over short distances, that is, a decrement is characteristic;

2) impulse, spreading excitation. It is characterized by:

a) the presence of a latent period of excitation;

b) the presence of a threshold of irritation;

c) the absence of a gradual character (it occurs abruptly);

d) distribution without decrement;

e) refractoriness (excitability of the tissue decreases).

Braking - an active process, occurs when stimuli act on the tissue, manifests itself in the suppression of another excitation. Consequently, there is no functional departure of the tissue.

Inhibition can only develop in the form of a local response.

There are two types of braking:

1) primary, for the occurrence of which the presence of special inhibitory neurons is necessary. Inhibition occurs primarily without prior excitation;

2) secondary, which does not require special brake structures. It arises as a result of a change in the functional activity of ordinary excitable structures.

The processes of excitation and inhibition are closely related, occur simultaneously and are different manifestations of a single process. The foci of excitation and inhibition are mobile, cover larger or smaller areas of neuronal populations, and can be more or less pronounced. Excitation will certainly be replaced by inhibition, and vice versa, i.e., there are inductive relations between inhibition and excitation.

4. Physical and chemical mechanisms of the emergence of the resting potential

Membrane potential (or resting potential) is the potential difference between the outer and inner surface of the membrane in a state of relative physiological rest. The resting potential arises as a result of two reasons:

1) uneven distribution of ions on both sides of the membrane. Inside the cell there is most of the K ions, outside it is little. There are more Na ions and Cl ions outside than inside. This distribution of ions is called ionic asymmetry;

2) selective permeability of the membrane for ions. At rest, the membrane is not equally permeable to different ions. The cell membrane is permeable to K ions, slightly permeable to Na ions, and impermeable to organic substances.

Due to these two factors, conditions are created for the movement of ions. This movement occurs without energy consumption through passive transport - diffusion as a result of the difference in ion concentration. K ions leave the cell and increase the positive charge on the outer surface of the membrane, Cl ions passively move into the cell, which leads to an increase in the positive charge on the outer surface of the cell. Na ions accumulate on the outer surface of the membrane and increase its positive charge. Organic compounds remain inside the cell. As a result of this movement, the outer surface of the membrane is charged positively, and the inner surface is charged negatively. The inner surface of the membrane may not be absolutely negatively charged, but it is always negatively charged relative to the outer surface. This state of the cell membrane is called a state of polarization. The movement of ions continues until the potential difference on the membrane is balanced, i.e., electrochemical equilibrium occurs. The moment of equilibrium depends on two forces:

1) diffusion forces;

2) forces of electrostatic interaction.

The value of electrochemical equilibrium:

1) maintenance of ionic asymmetry;

2) maintaining the value of the membrane potential at a constant level.

The diffusion force (difference in ion concentration) and the force of electrostatic interaction are involved in the occurrence of the membrane potential, therefore the membrane potential is called concentration-electrochemical.

To maintain ionic asymmetry, electrochemical equilibrium is not enough. The cell has another mechanism - the sodium-potassium pump. The sodium-potassium pump is a mechanism for ensuring active transport of ions. The cell membrane has a system of transporters, each of which binds three Na ions that are inside the cell and carries them out. From the outside, the transporter binds to two K ions located outside the cell and transports them into the cytoplasm. Energy is obtained from the breakdown of ATP. The operation of the sodium-potassium pump ensures:

1) a high concentration of K ions inside the cell, i.e., a constant value of the resting potential;

2) a low concentration of Na ions inside the cell, that is, it maintains normal osmolarity and cell volume, creates the basis for generating an action potential;

3) a stable concentration gradient of Na ions, facilitating the transport of amino acids and sugars.

5. Physico-chemical mechanisms of action potential occurrence

action potential - this is a shift in the membrane potential that occurs in the tissue under the action of a threshold and suprathreshold stimulus, which is accompanied by a recharge of the cell membrane.

When exposed to a threshold or suprathreshold stimulus, the permeability of the cell membrane for ions changes to varying degrees. For Na ions it increases by 400-500 times, and the gradient increases quickly, for K ions - by 10-15 times, and the gradient develops slowly. As a result, Na ions move into the cell, K ions move out of the cell, which leads to recharging of the cell membrane. The outer surface of the membrane carries a negative charge, while the inner surface carries a positive charge.

Action potential components:

1) local response;

2) high-voltage peak potential (spike);

3) trace vibrations:

a) negative trace potential;

b) positive trace potential.

local response.

Until the stimulus reaches 50-75% of the threshold at the initial stage, the permeability of the cell membrane remains unchanged, and the electrical shift of the membrane potential is explained by the irritating agent. Having reached the level of 50-75%, the activation gates (m-gates) of Na-channels open, and a local response occurs.

Na ions enter the cell by simple diffusion without expenditure of energy. Having reached the threshold strength, the membrane potential decreases to a critical level of depolarization (approximately 50 mV). The critical level of depolarization is the number of millivolts by which the membrane potential must decrease in order for an avalanche-like flow of Na ions into the cell to occur. If the strength of stimulation is insufficient, then a local response does not occur.

High voltage peak potential (spike).

The action potential peak is a constant component of the action potential. It consists of two phases:

1) ascending part - phases of depolarization;

2) descending part - phases of repolarization.

An avalanche-like flow of Na ions into the cell leads to a change in the potential on the cell membrane. The more Na ions enter the cell, the more the membrane depolarizes, the more activation gates open. Gradually, the charge is removed from the membrane, and then arises with the opposite sign. The appearance of a charge with the opposite sign is called the inversion of the membrane potential. The movement of Na ions into the cell continues until the moment of electrochemical equilibrium for the Na ion. The amplitude of the action potential does not depend on the strength of the stimulus, it depends on the concentration of Na ions and on the degree of permeability of the membrane to Na ions. The descending phase (repolarization phase) returns the membrane charge to its original sign. Upon reaching the electrochemical equilibrium for Na ions, the activation gate is inactivated, the permeability to Na ions decreases and the permeability to K ions increases, the sodium-potassium pump comes into action and restores the charge of the cell membrane. Full recovery of the membrane potential does not occur.

During the process of reduction reactions, trace potentials are recorded on the cell membrane - positive and negative. Trace potentials are non-sustained components of the action potential. Negative trace potential is a trace depolarization as a result of increased membrane permeability to Na ions, which inhibits the repolarization process. A positive trace potential occurs when the cell membrane is hyperpolarized in the process of restoring the cellular charge due to the release of potassium ions and the operation of the sodium-potassium pump.

LECTURE No. 3. Physiological properties of nerves and nerve fibers

1. Physiology of nerves and nerve fibers. Types of nerve fibers

Physiological properties of nerve fibers:

1) excitability - the ability to come into a state of excitement in response to irritation;

2) conductivity - the ability to transmit nerve excitation in the form of an action potential from the site of irritation along the entire length;

3) refractoriness (stability) - the property of temporarily sharply reducing excitability in the process of excitation.

Nervous tissue has the shortest refractory period. The value of refractoriness is to protect the tissue from overexcitation, to carry out a response to a biologically significant stimulus;

4) lability - the ability to respond to irritation with a certain speed. Lability is characterized by the maximum number of excitation impulses for a certain period of time (1 s) in exact accordance with the rhythm of the applied stimuli.

Nerve fibers are not independent structural elements of the nervous tissue, they are a complex formation, including the following elements:

1) processes of nerve cells - axial cylinders;

2) glial cells;

3) connective tissue (basal) plate.

The main function of nerve fibers is to conduct nerve impulses. The processes of nerve cells conduct the nerve impulses themselves, and glial cells contribute to this conduction. According to the structural features and functions, nerve fibers are divided into two types: unmyelinated and myelinated.

Unmyelinated nerve fibers do not have a myelin sheath. Their diameter is 5-7 microns, the speed of impulse conduction is 1-2 m/s. Myelin fibers consist of an axial cylinder covered by a myelin sheath formed by Schwann cells. The axial cylinder has a membrane and oxoplasm. The myelin sheath consists of 80% lipids with high ohmic resistance and 20% protein. The myelin sheath does not completely cover the axial cylinder, but is interrupted and leaves open areas of the axial cylinder, which are called nodal intercepts (Ranvier intercepts). The length of the sections between the intercepts is different and depends on the thickness of the nerve fiber: the thicker it is, the longer the distance between the intercepts. With a diameter of 12-20 microns, the speed of excitation is 70-120 m/s.

Depending on the speed of conduction of excitation, nerve fibers are divided into three types: A, B, C.

Type A fibers have the highest excitation conduction speed, the excitation conduction speed of which reaches 120 m / s, B has a speed of 3 to 14 m / s, C - from 0,5 to 2 m / s.

The concepts of "nerve fiber" and "nerve" should not be confused. Nerve - a complex formation consisting of a nerve fiber (myelinated or unmyelinated), loose fibrous connective tissue that forms the nerve sheath.

2. Mechanisms of conduction of excitation along the nerve fiber. Laws of conduction of excitation along the nerve fiber

The mechanism of conduction of excitation along the nerve fibers depends on their type. There are two types of nerve fibers: myelinated and unmyelinated.

Metabolic processes in unmyelinated fibers do not provide rapid compensation for energy expenditure. The spread of excitation will occur with gradual attenuation - with decrement. Decremental behavior of excitation is characteristic of a low-organized nervous system. Excitation propagates due to small circular currents that arise into the fiber or into the surrounding liquid. A potential difference arises between excited and unexcited areas, which contributes to the emergence of circular currents. The current will spread from the "+" charge to the "-". At the point where the circular current exits, the permeability of the plasma membrane for Na ions increases, resulting in depolarization of the membrane. A potential difference again arises between the newly excited area and the neighboring unexcited one, which leads to the emergence of circular currents. The excitation gradually covers neighboring areas of the axial cylinder and thus spreads to the end of the axon.

In myelin fibers, thanks to the perfection of metabolism, excitation passes without fading, without decrement. Due to the large radius of the nerve fiber, due to the myelin sheath, the electric current can enter and leave the fiber only in the area of interception. When irritation is applied, depolarization occurs in the area of intercept A, the adjacent intercept B is polarized at this time. Between the interceptions, a potential difference arises, and circular currents appear. Due to the circular currents, other interceptions are excited, while the excitation spreads in a saltatory way, abruptly from one interception to another. The saltatory method of spreading excitation is economical, and the speed of spreading excitation is much higher (70-120 m/s) than along unmyelinated nerve fibers (0,5-2 m/s).

There are three laws of conduction of irritation along the nerve fiber.

The law of anatomical and physiological integrity.

Conduction of impulses along the nerve fiber is possible only if its integrity is not violated. If the physiological properties of the nerve fiber are violated by cooling, the use of various drugs, squeezing, as well as cuts and damage to the anatomical integrity, it will be impossible to conduct a nerve impulse through it.

The law of isolated conduction of excitation.

There are a number of features of the spread of excitation in peripheral, pulpy and non-pulmonic nerve fibers.

In peripheral nerve fibers, excitation is transmitted only along the nerve fiber, but is not transmitted to neighboring nerve fibers that are in the same nerve trunk.

In the pulpy nerve fibers, the role of an insulator is performed by the myelin sheath. Due to myelin, the resistivity increases and the electrical capacitance of the shell decreases.

In the non-fleshy nerve fibers, excitation is transmitted in isolation. This is due to the fact that the resistance of the fluid that fills the intercellular gaps is much lower than the resistance of the nerve fiber membrane. Therefore, the current that occurs between the depolarized area and the non-polarized one passes through the intercellular gaps and does not enter the adjacent nerve fibers.

The law of bilateral excitation.

The nerve fiber conducts nerve impulses in two directions - centripetally and centrifugally.

In a living organism, excitation is carried out in only one direction. The two-way conduction of a nerve fiber is limited in the body by the place of origin of the impulse and by the valvular property of the synapses, which consists in the possibility of conducting excitation in only one direction.

LECTURE No. 4. Physiology of muscles

1. Physical and physiological properties of skeletal, cardiac and smooth muscles

According to morphological features, three groups of muscles are distinguished:

1) striated muscles (skeletal muscles);

2) smooth muscles;

3) cardiac muscle (or myocardium).

Functions of the striated muscles:

1) motor (dynamic and static);

2) ensuring breathing;

3) mimic;

4) receptor;

5) depositor;

6) thermoregulatory.

Smooth muscle functions:

1) maintaining pressure in hollow organs;

2) regulation of pressure in blood vessels;

3) emptying of hollow organs and promotion of their contents.

Function of the heart muscle - pumping, ensuring the movement of blood through the vessels.

Physiological properties of skeletal muscles:

1) excitability (lower than in the nerve fiber, which is explained by the low value of the membrane potential);

2) low conductivity, about 10-13 m/s;

3) refractoriness (takes a longer period of time than that of a nerve fiber);

4) lability;

5) contractility (the ability to shorten or develop tension).

There are two types of reduction:

a) isotonic contraction (length changes, tone does not change);

b) isometric contraction (the tone changes without changing the length of the fiber). There are single and titanic contractions. Single contractions occur under the action of a single stimulus, and titanic contractions occur in response to a series of nerve impulses;

6) elasticity (the ability to develop stress when stretched).

Physiological features of smooth muscles.

Smooth muscles have the same physiological properties as skeletal muscles, but they also have their own characteristics:

1) unstable membrane potential, which maintains the muscles in a state of constant partial contraction - tone;

2) spontaneous automatic activity;

3) contraction in response to stretching;

4) plasticity (decrease in stretching with increasing stretching);

5) high sensitivity to chemicals.

Physiological features of the heart muscle is her automatism. Excitation occurs periodically under the influence of processes occurring in the muscle itself. The ability to automatism have certain atypical muscle areas of the myocardium, poor in myofibrils and rich in sarcoplasm.

2. Mechanisms of muscle contraction

Electrochemical stage of muscle contraction.

1. Generation of action potential. The transfer of excitation to the muscle fiber occurs with the help of acetylcholine. The interaction of acetylcholine (ACh) with cholinergic receptors leads to their activation and the appearance of an action potential, which is the first stage of muscle contraction.

2. Propagation of the action potential. The action potential propagates inside the muscle fiber along the transverse system of tubules, which is the connecting link between the surface membrane and the contractile apparatus of the muscle fiber.

3. Electrical stimulation of the contact site leads to the activation of the enzyme and the formation of inosyl triphosphate, which activates the calcium channels of the membranes, which leads to the release of Ca ions and an increase in their intracellular concentration.

Chemomechanical stage of muscle contraction.

The theory of the chemomechanical stage of muscle contraction was developed by O. Huxley in 1954 and supplemented in 1963 by M. Davis. The main provisions of this theory:

1) Ca ions trigger the mechanism of muscle contraction;

2) due to Ca ions, thin actin filaments slide relative to myosin filaments.

At rest, when there are few Ca ions, sliding does not occur, because troponin molecules and the negative charges of ATP, ATPase, and ADP prevent this. An increased concentration of Ca ions occurs due to its entry from the interfibrillar space. In this case, a number of reactions occur with the participation of Ca ions:

1) Ca²⁺ reacts with tryponin;

2) Ca²⁺ activates ATPase;

3) Ca²⁺ removes charges from ADP, ATP, ATPase.

The interaction of Ca ions with troponin leads to a change in the location of the latter on the actin filament, and the active centers of a thin protofibril open. Due to them, transverse bridges are formed between actin and myosin, which move the actin filament into the gaps between the myosin filament. When the actin filament moves relative to the myosin filament, muscle tissue contracts.

So, the main role in the mechanism of muscle contraction is played by the troponin protein, which closes the active centers of the thin protofibril and Ca ions.

LECTURE No. 5. Physiology of synapses

1. Physiological properties of synapses, their classification

Synapse - This is a structural and functional formation that ensures the transition of excitation or inhibition from the end of the nerve fiber to the innervating cell.

Synapse structure:

1) presynaptic membrane (electrogenic membrane in the axon terminal, forms a synapse on the muscle cell);

2) postsynaptic membrane (electrogenic membrane of the innervated cell on which the synapse is formed);

3) synaptic cleft (the space between the presynaptic and postsynaptic membranes is filled with a fluid that resembles blood plasma in composition).

There are several classifications of synapses.

1. By localization:

1) central synapses;

2) peripheral synapses.

Central synapses lie within the central nervous system and are also found in the ganglia of the autonomic nervous system. Central synapses are contacts between two nerve cells, and these contacts are heterogeneous and, depending on the structure on which the first neuron forms a synapse with the second neuron, they are distinguished:

1) axosomatic, formed by the axon of one neuron and the body of another neuron;

2) axodendritic, formed by the axon of one neuron and the dendrite of another;

3) axoaxonal (the axon of the first neuron forms a synapse on the axon of the second neuron);

4) dendrodentritic (the dendrite of the first neuron forms a synapse on the dendrite of the second neuron).

There are several types of peripheral synapses:

1) myoneural (neuromuscular), formed by the axon of a motor neuron and a muscle cell;

2) neuro-epithelial, formed by the axon of the neuron and the secretory cell.

2. Functional classification of synapses:

1) excitatory synapses;

2) inhibitory synapses.

3. According to the mechanisms of excitation transmission in synapses:

1) chemical;

2) electrical.

The peculiarity of chemical synapses is that the transmission of excitation is carried out using a special group of chemicals - mediators.

There are several types of chemical synapses:

1) cholinergic. In them, the transfer of excitation occurs with the help of acetylcholine;

2) adrenergic. In them, the transfer of excitation occurs with the help of three catecholamines;

3) dopaminergic. They transmit excitation with the help of dopamine;

4) histaminergic. In them, the transfer of excitation occurs with the help of histamine;

5) GABAergic. In them, excitation is transferred with the help of gamma-aminobutyric acid, i.e., the process of inhibition develops.

A feature of electrical synapses is that the transmission of excitation is carried out using an electric current. Few such synapses have been found in the body.

Synapses have a number of physiological properties:

1) the valvular property of synapses, i.e., the ability to transmit excitation in only one direction from the presynaptic membrane to the postsynaptic one;

2) the property of synaptic delay, due to the fact that the rate of transmission of excitation is reduced;

3) the property of potentiation (each subsequent impulse will be carried out with a smaller postsynaptic delay). This is due to the fact that the mediator from the previous impulse remains on the presynaptic and postsynaptic membrane;

4) low lability of the synapse (100-150 impulses per second).

2. Mechanisms of excitation transmission in synapses using the example of a myoneural synapse

Mioneural (neuromuscular) synapse - formed by the axon of a motor neuron and a muscle cell.

The nerve impulse originates in the trigger zone of the neuron, travels along the axon to the innervated muscle, reaches the axon terminal, and at the same time depolarizes the presynaptic membrane. After that, sodium and calcium channels open, and Ca ions from the environment surrounding the synapse enter the axon terminal. In this process, the Brownian movement of the vesicles is ordered towards the presynaptic membrane. Ca ions stimulate the movement of vesicles. Upon reaching the presynaptic membrane, the vesicles rupture and release acetylcholine (4 Ca ions release 1 quantum of acetylcholine). The synaptic cleft is filled with a fluid that resembles blood plasma in composition, diffusion of ACh from the presynaptic membrane to the postsynaptic membrane occurs through it, but its speed is very low. In addition, diffusion is also possible along the fibrous filaments that are located in the synaptic cleft. After diffusion, ACh begins to interact with chemoreceptors (ChR) and cholinesterase (ChE) located on the postsynaptic membrane.

The cholinergic receptor performs a receptor function, and cholinesterase performs an enzymatic function. On the postsynaptic membrane they are located as follows:

XP-XE-XP-XE-XP-XE.

XP + AH \uXNUMXd MECP - miniature end plate potentials.

Then the MECP is summed. As a result of the summation, an EPSP is formed - excitatory postsynaptic potential. The postsynaptic membrane is negatively charged due to EPSP, and in the area where there is no synapse (muscle fiber), the charge is positive. A potential difference arises, an action potential is formed, which moves along the conduction system of the muscle fiber.

ChE + ACh = destruction of ACh to choline and acetic acid.

In a state of relative physiological rest, the synapse is in background bioelectrical activity. Its significance lies in the fact that it increases the readiness of the synapse to conduct a nerve impulse. At rest, 1-2 vesicles in the axon terminal may accidentally approach the presynaptic membrane, as a result of which they will come into contact with it. The vesicle bursts on contact with the presynaptic membrane, and its contents in the form of 1 quantum of ACh enter the synaptic cleft, falling on the postsynaptic membrane, where MPN will be formed.

3. Physiology of mediators. Classification and characteristics

Mediator - this is a group of chemicals that takes part in the transfer of excitation or inhibition in chemical synapses from the presynaptic to the postsynaptic membrane.

Criteria by which a substance is classified as a mediator:

1) the substance must be released on the presynaptic membrane, the axon terminal;

2) in the structures of the synapse, there must be enzymes that promote the synthesis and breakdown of the mediator, and there must also be receptors on the postsynaptic membrane that interact with the mediator;

3) a substance that claims to be a mediator must, at a very low concentration, transmit excitation from the presynaptic membrane to the postsynaptic membrane. Classification of mediators:

1) chemical, based on the structure of the mediator;

2) functional, based on the function of the mediator.

Chemical classification.

1. Esters - acetylcholine (AH).

2. Biogenic amines:

1) catecholamines (dopamine, norepinephrine (HA), adrenaline (A));

2) serotonin;

3) histamine.

3. Amino acids:

1) gamma-aminobutyric acid (GABA);

2) glutamic acid;

3) glycine;

4) arginine.

4. Peptides:

1) opioid peptides:

a) methenkephalin;

b) enkephalins;

c) leuenkephalins;

2) substance "P";

3) vasoactive intestinal peptide;

4) somatostatin.

5. Purine compounds: ATP.

6. Substances with a minimum molecular weight:

1) NO;

2) CO.

Functional classification.

1. Excitatory mediators that cause depolarization of the postsynaptic membrane and the formation of an excitatory postsynaptic potential:

1) AH;

2) glutamic acid;

3) aspartic acid.

2. Inhibitory mediators that cause hyperpolarization of the postsynaptic membrane, after which an inhibitory postsynaptic potential arises, which generates the process of inhibition:

1) GABA;

2) glycine;

3) substance "P";

4) dopamine;

5) serotonin;

6) ATP.

Norepinephrine, isonoradrenaline, epinephrine, histamine are both inhibitory and excitatory.

AH (acetylcholine) is the most common mediator in the central nervous system and in the peripheral nervous system. The content of ACh in various structures of the nervous system is not the same. From a phylogenetic point of view, the concentration of acetylcholine is higher in older structures of the nervous system than in younger ones. ACh is found in tissues in two states: bound to proteins or in a free state (the active mediator is only in this state).

ACh is formed from the amino acid choline and acetyl coenzyme A.

Mediators in adrenergic synapses are norepinephrine, isonoradrenaline, adrenaline. The formation of catecholamines occurs in the vesicles of the axon terminal, the source is the amino acid: phenylalanine (FA).

LECTURE No. 6. Physiology of the central nervous system

1. Basic principles of the functioning of the central nervous system. Structure, functions, methods of studying the central nervous system

The main principle of the functioning of the central nervous system is the process of regulation, control of physiological functions, which are aimed at maintaining the constancy of the properties and composition of the internal environment of the body. The central nervous system ensures the optimal relationship of the organism with the environment, stability, integrity, and the optimal level of vital activity of the organism.

There are two main types of regulation: humoral and nervous.

The humoral control process involves a change in the physiological activity of the body under the influence of chemicals that are delivered by the liquid media of the body. The source of information transfer is chemical substances - utilizons, metabolic products (carbon dioxide, glucose, fatty acids), informons, hormones of endocrine glands, local or tissue hormones.

The nervous process of regulation provides for the control of changes in physiological functions along nerve fibers with the help of an excitation potential under the influence of information transmission.

Characteristics:

1) is a later product of evolution;

2) provides fast handling;

3) has an exact addressee of the impact;

4) implements an economical way of regulation;

5) provides high reliability of information transmission.

In the body, the nervous and humoral mechanisms work as a single system of neurohumoral control. This is a combined form, where two control mechanisms are used simultaneously, they are interconnected and interdependent.

The nervous system is a collection of nerve cells, or neurons.

According to localization, they distinguish:

1) the central section - the brain and spinal cord;

2) peripheral - processes of nerve cells of the brain and spinal cord.

According to functional features, they distinguish:

1) somatic department that regulates motor activity;

2) vegetative, regulating the activity of internal organs, endocrine glands, blood vessels, trophic innervation of muscles and the central nervous system itself.

Functions of the nervous system:

1) integrative-coordination function. Provides the functions of various organs and physiological systems, coordinates their activities with each other;

2) ensuring close connections of the human body with the environment at the biological and social levels;

3) regulation of the level of metabolic processes in various organs and tissues, as well as in itself;

4) ensuring mental activity by the higher departments of the central nervous system.

2. Neuron. Structural features, meaning, types

The structural and functional unit of nervous tissue is the nerve cell - neuron.

A neuron is a specialized cell that is able to receive, encode, transmit and store information, establish contacts with other neurons, and organize the body's response to irritation.

Functionally in a neuron, there are:

1) the receptive part (the dendrites and the membrane of the soma of the neuron);

2) integrative part (soma with axon hillock);

3) the transmitting part (axon hillock with axon).

The receiving part.

Dendrites - the main perceiving field of the neuron. The dendrite membrane is able to respond to neurotransmitters. The neuron has several branching dendrites. This is explained by the fact that a neuron as an information formation must have a large number of inputs. Through specialized contacts, information flows from one neuron to another. These contacts are called spikes.

The neuron soma membrane is 6 nm thick and consists of two layers of lipid molecules. The hydrophilic ends of these molecules face the water phase: one layer of molecules faces inward, the other outward. The hydrophilic ends are turned towards each other - inside the membrane. The lipid bilayer of the membrane contains proteins that perform several functions:

1) pump proteins - move ions and molecules in the cell against the concentration gradient;

2) proteins built into the channels provide selective membrane permeability;

3) receptor proteins recognize the desired molecules and fix them on the membrane;

4) enzymes facilitate the flow of a chemical reaction on the surface of the neuron.

In some cases, the same protein can function as both a receptor, an enzyme, and a pump.

integrative part.

axon hillock the exit point of an axon from a neuron.

The soma of a neuron (the body of a neuron) performs, along with an informational and trophic function, regarding its processes and synapses. The soma provides the growth of dendrites and axons. The soma of the neuron is enclosed in a multilayer membrane, which ensures the formation and distribution of the electrotonic potential to the axon hillock.

Transmitting part.

Axon - an outgrowth of the cytoplasm adapted to carry information that is collected by dendrites and processed in a neuron. The axon of a dendritic cell has a constant diameter and is covered with a myelin sheath, which is formed from glia; the axon has branched endings that contain mitochondria and secretory formations.

Functions of neurons:

1) generalization of the nerve impulse;

2) receipt, storage and transmission of information;

3) the ability to summarize excitatory and inhibitory signals (integrative function).

Types of neurons:

1) by localization:

a) central (brain and spinal cord);

b) peripheral (cerebral ganglia, cranial nerves);

2) depending on the function:

a) afferent (sensitive), carrying information from receptors in the central nervous system;

b) intercalary (connector), in the elementary case, providing a connection between the afferent and efferent neurons;

c) efferent:

- motor - anterior horns of the spinal cord;

- secretory - lateral horns of the spinal cord;

3) depending on the functions:

a) exciting;

b) inhibitory;

4) depending on the biochemical characteristics, on the nature of the mediator;

5) depending on the quality of the stimulus that is perceived by the neuron:

a) monomodal;

b) polymodal.

3. Reflex arc, its components, types, functions

The activity of the body is a natural reflex reaction to a stimulus. Reflex - the reaction of the body to irritation of receptors, which is carried out with the participation of the central nervous system. The structural basis of the reflex is the reflex arc.

Reflex arc - a chain of nerve cells connected in series, which ensures the implementation of a reaction, a response to irritation.

The reflex arc consists of six components: receptors, afferent (sensory) pathway, reflex center, efferent (motor, secretory) pathway, effector (working organ), feedback.

Reflex arcs can be of two types:

1) simple - monosynaptic reflex arcs (reflex arc of the tendon reflex), consisting of 2 neurons (receptor (afferent) and effector), there is 1 synapse between them;

2) complex - polysynaptic reflex arcs. They include 3 neurons (there may be more) - receptor, one or more intercalary and effector.

The idea of a reflex arc as an expedient response of the body dictates the need to supplement the reflex arc with another link - a feedback loop. This component establishes a connection between the realized result of the reflex reaction and the nerve center that issues executive commands. With the help of this component, the open reflex arc is transformed into a closed one.

Features of a simple monosynaptic reflex arc:

1) geographically close receptor and effector;

2) the reflex arc is two-neuron, monosynaptic;

3) nerve fibers of group Aα (70-120 m/s);

4) short reflex time;

5) muscles that contract as a single muscle contraction.

Features of a complex monosynaptic reflex arc:

1) territorially separated receptor and effector;

2) the receptor arc is three-neuronal (maybe more neurons);

3) the presence of nerve fibers of groups C and B;

4) muscle contraction by the type of tetanus.

Features of the autonomic reflex:

1) the intercalary neuron is located in the lateral horns;

2) the preganglionic nerve path begins from the lateral horns, after the ganglion - the postganglionic one;

3) the efferent path of the reflex of the autonomic neural arch is interrupted by the autonomic ganglion, in which the efferent neuron lies.

The difference between the sympathetic neural arch and the parasympathetic one: in the sympathetic neural arch, the preganglionic path is short, since the autonomic ganglion lies closer to the spinal cord, and the postganglionic path is long.

In the parasympathetic arch, the opposite is true: the preganglionic path is long, since the ganglion lies close to the organ or in the organ itself, and the postganglionic path is short.

4. Functional systems of the body

Functional system - temporary functional association of the nerve centers of various organs and systems of the body to achieve the final beneficial result.

A useful result is a self-forming factor of the nervous system. The result of the action is a vital adaptive indicator that is necessary for the normal functioning of the body.

There are several groups of end useful results:

1) metabolic - a consequence of metabolic processes at the molecular level, which create substances and end products necessary for life;

2) homeostatic - the constancy of indicators of the state and composition of the body's environments;

3) behavioral - the result of a biological need (sexual, food, drinking);

4) social - satisfaction of social and spiritual needs.

The functional system includes various organs and systems, each of which takes an active part in achieving a useful result.

The functional system, according to P.K. Anokhin, includes five main components:

1) a useful adaptive result - something for which a functional system is created;

2) control apparatus (result acceptor) - a group of nerve cells in which a model of the future result is formed;

3) reverse afferentation (supplies information from the receptor to the central link of the functional system) - secondary afferent nerve impulses that go to the acceptor of the result of the action to evaluate the final result;

4) control apparatus (central link) - functional association of nerve centers with the endocrine system;

5) executive components (reaction apparatus) are the organs and physiological systems of the body (vegetative, endocrine, somatic). Consists of four components:

a) internal organs;

b) endocrine glands;

c) skeletal muscles;

d) behavioral responses.

Functional system properties:

1) dynamism. The functional system may include additional organs and systems, depending on the complexity of the situation;

2) the ability to self-regulation. When the controlled value or the final useful result deviates from the optimal value, a series of spontaneous complex reactions occur, which returns the indicators to the optimal level. Self-regulation is carried out in the presence of feedback.

Several functional systems work simultaneously in the body. They are in continuous interaction, which is subject to certain principles:

1) the principle of the system of genesis. Selective maturation and evolution of functional systems take place (functional systems of blood circulation, respiration, nutrition, mature and develop earlier than others);

2) the principle of multiply connected interaction. There is a generalization of the activity of various functional systems, aimed at achieving a multicomponent result (parameters of homeostasis);

3) the principle of hierarchy. Functional systems are lined up in a certain row in accordance with their significance (functional tissue integrity system, functional nutrition system, functional reproduction system, etc.);

4) the principle of consistent dynamic interaction. There is a clear sequence of changing the activity of one functional system of another.

5. Coordinating activity of the CNS

Coordination activity (CA) of the CNS is a coordinated work of CNS neurons based on the interaction of neurons with each other.

CD functions:

1) provides a clear performance of certain functions, reflexes;

2) ensures the consistent inclusion in the work of various nerve centers to ensure complex forms of activity;

3) ensures the coordinated work of various nerve centers (during the act of swallowing, the breath is held at the moment of swallowing, when the swallowing center is excited, the respiratory center is inhibited).

Basic principles of CNS CD and their neural mechanisms.

1. The principle of irradiation (spread). When small groups of neurons are excited, the excitation spreads to a significant number of neurons. Irradiation is explained:

1) the presence of branched endings of axons and dendrites, due to branching, impulses propagate to a large number of neurons;

2) the presence of intercalary neurons in the CNS, which ensure the transmission of impulses from cell to cell. Irradiation has a boundary, which is provided by an inhibitory neuron.

2. The principle of convergence. When a large number of neurons are excited, the excitation can converge to one group of nerve cells.

3. The principle of reciprocity - the coordinated work of the nerve centers, especially in opposite reflexes (flexion, extension, etc.).

4. The principle of dominance. Dominant - the dominant focus of excitation in the central nervous system at the moment. This is a focus of persistent, unwavering, non-spreading excitation. It has certain properties: it suppresses the activity of other nerve centers, has increased excitability, attracts nerve impulses from other foci, summarizes nerve impulses. Foci of the dominant are of two types: exogenous origin (caused by environmental factors) and endogenous (caused by environmental factors). The dominant underlies the formation of a conditioned reflex.

5. The principle of feedback. Feedback - the flow of impulses to the nervous system, which informs the central nervous system about how the response is carried out, whether it is sufficient or not. There are two types of feedback:

1) positive feedback, causing an increase in the response from the nervous system. Underlies a vicious circle that leads to the development of diseases;

2) negative feedback, which reduces the activity of CNS neurons and the response. Underlies self-regulation.

6. The principle of subordination. In the CNS, there is a certain subordination of departments to each other, the highest department is the cerebral cortex.

7. The principle of interaction between the processes of excitation and inhibition. The central nervous system coordinates the processes of excitation and inhibition:

both processes are capable of convergence, the process of excitation and, to a lesser extent, inhibition, are capable of irradiation. Inhibition and excitation are connected by inductive relationships. The process of excitation induces inhibition, and vice versa. There are two types of induction:

1) consistent. The process of excitation and inhibition replace each other in time;

2) mutual. At the same time, there are two processes - excitation and inhibition. Mutual induction is carried out by positive and negative mutual induction: if inhibition occurs in a group of neurons, then foci of excitation arise around it (positive mutual induction), and vice versa.

According to IP Pavlov's definition, excitation and inhibition are two sides of the same process. The coordination activity of the CNS provides a clear interaction between individual nerve cells and individual groups of nerve cells. There are three levels of integration.

The first level is provided due to the fact that impulses from different neurons can converge on the body of one neuron, as a result, either summation or a decrease in excitation occurs.

The second level provides interactions between separate groups of cells.

The third level is provided by the cells of the cerebral cortex, which contribute to a more perfect level of adaptation of the activity of the central nervous system to the needs of the body.

6. Types of inhibition, interaction of the processes of excitation and inhibition in the central nervous system. Experience of I. M. Sechenov

Braking - an active process that occurs under the action of stimuli on the tissue, manifests itself in the suppression of another excitation, there is no functional administration of the tissue.

Inhibition can only develop in the form of a local response.

There are two types of braking:

1) primary. For its occurrence, the presence of special inhibitory neurons is necessary. Inhibition occurs primarily without prior excitation under the influence of an inhibitory mediator. There are two types of primary inhibition:

a) presynaptic in the axo-axonal synapse;

b) postsynaptic in the axodendric synapse.

2) secondary. It does not require special inhibitory structures, it arises as a result of a change in the functional activity of ordinary excitable structures, it is always associated with the process of excitation. Types of secondary braking:

a) beyond, arising from a large flow of information entering the cell. The flow of information lies outside the neuron's performance;

b) pessimal, arising at a high frequency of irritation;

c) parabiotic, arising from strong and long-acting irritation;

d) inhibition following excitation, resulting from a decrease in the functional state of neurons after excitation;

e) braking according to the principle of negative induction;

f) inhibition of conditioned reflexes.

The processes of excitation and inhibition are closely related, occur simultaneously and are different manifestations of a single process. The foci of excitation and inhibition are mobile, cover larger or smaller areas of neuronal populations, and may be more or less pronounced. Excitation will certainly be replaced by inhibition, and vice versa, i.e., there are inductive relations between inhibition and excitation.

Inhibition underlies the coordination of movements, protects the central neurons from overexcitation. Inhibition in the central nervous system can occur when nerve impulses of various strengths from several stimuli simultaneously enter the spinal cord. Stronger stimulation inhibits the reflexes that should have come in response to weaker ones.

In 1862, I. M. Sechenov discovered the phenomenon of central inhibition. He proved in his experiment that irritation of the visual tubercles of a frog (the large hemispheres of the brain were removed) causes inhibition of spinal cord reflexes with a sodium chloride crystal. After elimination of the stimulus, the reflex activity of the spinal cord was restored. The result of this experiment allowed I. M. Secheny to conclude that in the central nervous system, along with the process of excitation, a process of inhibition develops, which is capable of inhibiting the reflex acts of the body. N. E. Vvedensky suggested that the principle of negative induction underlies the phenomenon of inhibition: a more excitable section in the central nervous system inhibits the activity of less excitable sections.

Modern interpretation of the experience of I.M. Sechenov (I.M. Sechenov irritated the reticular formation of the brain stem): excitation of the reticular formation increases the activity of inhibitory neurons of the spinal cord - Renshaw cells, which leads to inhibition of α-motoneurons of the spinal cord and inhibits the reflex activity of the spinal cord.

7. Methods for studying the central nervous system

There are two large groups of methods for studying the CNS:

1) an experimental method that is carried out on animals;

2) a clinical method that is applicable to humans.

Among the experimental methods Classical physiology includes methods aimed at activating or suppressing the studied nerve formation. These include:

1) the method of transverse transection of the central nervous system at various levels;

2) method of extirpation (removal of various departments, denervation of the organ);

3) method of irritation by activation (adequate irritation - irritation with an electrical impulse similar to a nervous one; inadequate irritation - irritation with chemical compounds, graded irritation with electric current) or suppression (blocking the transmission of excitation under the influence of cold, chemical agents, direct current);

4) observation (one of the oldest method of studying the functioning of the central nervous system that has not lost its significance. It can be used independently, more often used in combination with other methods).

Experimental methods are often combined with each other when conducting an experiment.

clinical method aimed at studying the physiological state of the central nervous system in humans. It includes the following methods:

1) observation;

2) a method for recording and analyzing the electrical potentials of the brain (electro-, pneumo-, magnetoencephalography);

3) radioisotope method (explores neurohumoral regulatory systems);

4) conditioned reflex method (studies the functions of the cerebral cortex in the mechanism of learning, development of adaptive behavior);

5) the method of questioning (assesses the integrative functions of the cerebral cortex);

6) modeling method (mathematical modeling, physical, etc.). A model is an artificially created mechanism that has a certain functional similarity with the mechanism of the human body under study;

7) cybernetic method (studies control and communication processes in the nervous system). Aimed at studying organization (systemic properties of the nervous system at various levels), management (selection and implementation of influences necessary to ensure the functioning of an organ or system), information activity (the ability to perceive and process information - an impulse in order to adapt the body to environmental changes).

LECTURE No. 7. Physiology of various sections of the central nervous system

1. Physiology of the spinal cord

The spinal cord is the most ancient formation of the central nervous system. A characteristic feature of the structure is segmentation.

The neurons of the spinal cord form it Gray matter in the form of anterior and posterior horns. They perform a reflex function of the spinal cord.

The posterior horns contain neurons (interneurons) that transmit impulses to the overlying centers, to the symmetrical structures of the opposite side, to the anterior horns of the spinal cord. The posterior horns contain afferent neurons that respond to pain, temperature, tactile, vibration, and proprioceptive stimuli.

The anterior horns contain neurons (motoneurons) that give axons to the muscles, they are efferent. All descending pathways of the CNS for motor reactions terminate in the anterior horns.

In the lateral horns of the cervical and two lumbar segments there are neurons of the sympathetic division of the autonomic nervous system, in the second-fourth segments - of the parasympathetic.

The spinal cord contains many interneurons that provide communication with the segments and with the overlying parts of the central nervous system; they account for 97% of the total number of spinal cord neurons. They include associative neurons - neurons of the spinal cord's own apparatus; they establish connections within and between segments.

White matter the spinal cord is formed by myelin fibers (short and long) and performs a conductive role.

Short fibers connect neurons of one or different segments of the spinal cord.

Long fibers (projection) form the pathways of the spinal cord. They form ascending pathways to the brain and descending pathways from the brain.

The spinal cord performs reflex and conduction functions.

The reflex function allows you to realize all the motor reflexes of the body, reflexes of internal organs, thermoregulation, etc. Reflex reactions depend on the location, strength of the stimulus, the area of the reflexogenic zone, the speed of the impulse through the fibers, and the influence of the brain.

Reflexes are divided into:

1) exteroceptive (occur when irritated by environmental agents of sensory stimuli);

2) interoceptive (occur when irritating presso-, mechano-, chemo-, thermoreceptors): viscero-visceral - reflexes from one internal organ to another, viscero-muscular - reflexes from internal organs to skeletal muscles;

3) proprioceptive (own) reflexes from the muscle itself and its associated formations. They have a monosynaptic reflex arc. Proprioceptive reflexes regulate motor activity due to tendon and postural reflexes. Tendon reflexes (knee, Achilles, with the triceps of the shoulder, etc.) occur when the muscles are stretched and cause relaxation or muscle contraction, occur with every muscle movement;

4) postural reflexes (occur when the vestibular receptors are excited when the speed of movement and the position of the head relative to the body change, which leads to a redistribution of muscle tone (increase in extensor tone and decrease in flexors) and ensures body balance).

The study of proprioceptive reflexes is performed to determine the excitability and degree of damage to the central nervous system.

The conduction function ensures the connection of the neurons of the spinal cord with each other or with the overlying sections of the central nervous system.

2. Physiology of the hindbrain and midbrain

Structural formations of the hindbrain.

1. V-XII pair of cranial nerves.

2. Vestibular nuclei.

3. Kernels of the reticular formation.

The main functions of the hindbrain are conductive and reflex.

Descending tracts (corticospinal and extrapyramidal) and ascending tracts (reticulo- and vestibulospinal), which are responsible for the redistribution of muscle tone and maintaining body posture, pass through the hindbrain.

The reflex function provides:

1) protective reflexes (lacrimation, blinking, coughing, vomiting, sneezing);

2) the speech center provides reflexes of voice formation, the nuclei of the X, XII, VII cranial nerves, the respiratory center regulates the flow of air, the cerebral cortex is the speech center;

3) posture maintenance reflexes (labyrinth reflexes). Static reflexes maintain muscle tone to maintain body posture, statokinetic ones redistribute muscle tone to take a pose corresponding to the moment of rectilinear or rotational movement;

4) centers located in the hindbrain regulate the activity of many systems.

The vascular center regulates vascular tone, the respiratory center regulates inhalation and exhalation, the complex food center regulates the secretion of the gastric, intestinal glands, pancreas, liver secretory cells, salivary glands, provides sucking, chewing, swallowing reflexes.

Damage to the hindbrain leads to a loss of sensitivity, volitional motility, and thermoregulation, but breathing, blood pressure, and reflex activity are preserved.

Structural units of the midbrain:

1) tubercles of the quadrigemina;

2) red core;

3) black core;

4) nuclei of the III-IV pair of cranial nerves.

The tubercles of the quadrigemina perform an afferent function, the rest of the formations - an efferent one.

The quadrigeminal tuberosities closely interact with the nuclei of the III-IV pairs of cranial nerves, the red nucleus, and the optic tract. Due to this interaction, the anterior tubercles provide an indicative reflex reaction to light, and the rear tubercles - to sound. They provide vital reflexes: start reflex - a motor reaction to a sharp unusual stimulus (increased flexor tone), landmark reflex - a motor reaction to a new stimulus (rotation of the body, head).

The anterior tubercles with the nuclei of the III-IV cranial nerves provide a convergence reaction (convergence of the eyeballs to the midline), the movement of the eyeballs.

The red nucleus takes part in the regulation of the redistribution of muscle tone, in restoring the body posture (increases the tone of the flexors, lowers the tone of the extensors), maintains balance, and prepares the skeletal muscles for voluntary and involuntary movements.

The substantia nigra of the brain coordinates the act of swallowing and chewing, breathing, blood pressure (the pathology of the substantia nigra of the brain leads to an increase in blood pressure).

3. Physiology of the diencephalon

The diencephalon consists of the thalamus and hypothalamus, they connect the brain stem with the cerebral cortex.

Thalamus - pair formation, the largest accumulation of gray matter in the diencephalon.

Topographically, the anterior, middle, posterior, medial and lateral groups of nuclei are distinguished.

By function, they distinguish:

1) specific:

a) switching, relay. They receive primary information from various receptors. The nerve impulse along the thalamocortical tract goes to a strictly limited area of the cerebral cortex (primary projection zones), due to this, specific sensations arise. The nuclei of the ventrabasal complex receive an impulse from skin receptors, tendon proprioceptors, and ligaments. The impulse is sent to the sensorimotor zone, the body orientation in space is regulated. The lateral nuclei switch the impulse from the visual receptors to the occipital visual zone. The medial nuclei respond to a strictly defined sound wave length and conduct an impulse to the temporal zone;

b) associative (internal) nuclei. The primary impulse comes from the relay nuclei, is processed (an integrative function is carried out), transmitted to the associative zones of the cerebral cortex, the activity of the associative nuclei increases under the action of a painful stimulus;

2) non-specific nuclei. This is a non-specific way of transmitting impulses to the cerebral cortex, the frequency of the biopotential changes (modeling function);

3) motor nuclei involved in the regulation of motor activity. Impulses from the cerebellum, basal ganglia go to the motor zone, carry out the relationship, consistency, sequence of movements, spatial orientation of the body.

The thalamus is a collector of all afferent information, except for olfactory receptors, and is the most important integrative center.

Hypothalamus located on the bottom and sides of the third ventricle of the brain. Structures: gray tubercle, funnel, mastoid bodies. Zones: hypophysiotropic (preoptic and anterior nuclei), medial (middle nuclei), lateral (outer, posterior nuclei).

Physiological role - the highest subcortical integrative center of the autonomic nervous system, which has an effect on:

1) thermoregulation. The anterior nuclei are the center of heat transfer, where the process of sweating, respiratory rate and vascular tone are regulated in response to an increase in ambient temperature. The posterior nuclei are the center of heat production and the preservation of heat when the temperature drops;

2) pituitary. Liberins promote the secretion of hormones of the anterior pituitary gland, statins inhibit it;

3) fat metabolism. Irritation of the lateral (nutrition center) nuclei and ventromedial (satiation center) nuclei leads to obesity, inhibition leads to cachexia;

4) carbohydrate metabolism. Irritation of the anterior nuclei leads to hypoglycemia, the posterior nuclei to hyperglycemia;

5) the cardiovascular system. Irritation of the anterior nuclei has an inhibitory effect, the posterior nuclei - an activating one;

6) motor and secretory functions of the gastrointestinal tract. Irritation of the anterior nuclei increases motility and secretory function of the gastrointestinal tract, while the posterior nuclei inhibits sexual function. Destruction of nuclei leads to disruption of ovulation, spermatogenesis, and decreased sexual function;

7) behavioral responses. Irritation of the starting emotional zone (front nuclei) causes a feeling of joy, satisfaction, erotic feelings, the stop zone (rear nuclei) causes fear, feelings of anger, rage.

4. Physiology of the reticular formation and limbic system

Reticular formation of the brain stem - accumulation of polymorphic neurons along the brain stem.

Physiological feature of neurons of the reticular formation:

1) spontaneous bioelectrical activity. Its causes are humoral irritation (increase in the level of carbon dioxide, biologically active substances);

2) sufficiently high excitability of neurons;

3) high sensitivity to biologically active substances.

The reticular formation has wide bilateral connections with all parts of the nervous system; according to its functional significance and morphology, it is divided into two parts:

1) rastral (ascending) department - reticular formation of the diencephalon;

2) caudal (descending) - the reticular formation of the hindbrain, midbrain, bridge.

The physiological role of the reticular formation is the activation and inhibition of brain structures.

Limbic system - a collection of nuclei and nerve tracts.

Structural units of the limbic system:

1) olfactory bulb;

2) olfactory tubercle;

3) transparent partition;

4) hippocampus;

5) parahippocampal gyrus;

6) almond-shaped nuclei;

7) piriform gyrus;

8) dentate fascia;

9) cingulate gyrus.

The main functions of the limbic system:

1) participation in the formation of food, sexual, defensive instincts;

2) regulation of vegetative-visceral functions;

3) the formation of social behavior;

4) participation in the formation of the mechanisms of long-term and short-term memory;

5) performance of the olfactory function;

6) inhibition of conditioned reflexes, strengthening of unconditioned ones;

7) participation in the formation of the wakefulness-sleep cycle.

Significant formations of the limbic system are:

1) hippocampus. Its damage leads to a disruption in the process of memorization, information processing, a decrease in emotional activity, initiative, a slowdown in the speed of nervous processes, irritation leads to an increase in aggression, defensive reactions, and motor function. Hippocampal neurons are characterized by high background activity. Up to 60% of neurons react in response to sensory stimulation; the generation of excitation is expressed in a long-term reaction to a single short impulse;

2) amygdaloid nuclei. Their damage leads to the disappearance of fear, inability to aggression, hypersexuality, reactions to caring for offspring, irritation leads to a parasympathetic effect on the respiratory, cardiovascular, and digestive systems. Neurons of the amygdaloid nuclei have pronounced spontaneous activity, which is inhibited or enhanced by sensory stimuli;

3) olfactory bulb, olfactory tubercle.

The limbic system has a regulatory effect on the cerebral cortex.

5. Physiology of the cerebral cortex

The highest department of the central nervous system is the cerebral cortex, its area is 2200 cm².

The cerebral cortex has a five-, six-layer structure. Neurons are represented by sensory, motor (Betz cells), interneurons (inhibitory and excitatory neurons).

The cerebral cortex is built according to the columnar principle. Columns - functional units of the cortex, are divided into micromodules, which have homogeneous neurons.

According to IP Pavlov's definition, the cerebral cortex is the main manager and distributor of body functions.

The main functions of the cerebral cortex:

1) integration (thinking, consciousness, speech);

2) ensuring the connection of the organism with the external environment, its adaptation to its changes;

3) clarification of the interaction between the body and systems within the body;

4) coordination of movements (the ability to carry out voluntary movements, to make involuntary movements more accurate, to carry out motor tasks).

These functions are provided by corrective, triggering, integrative mechanisms.

I. P. Pavlov, creating the theory of analyzers, singled out three sections: peripheral (receptor), conductive (three-neural pathway for transmitting impulses from receptors), brain (certain areas of the cerebral cortex, where the processing of a nerve impulse takes place, which acquires a new quality ). The brain section consists of the analyzer nuclei and scattered elements.

According to modern ideas about the localization of functions, three types of fields arise during the passage of an impulse in the cerebral cortex.

1. The primary projection zone lies in the region of the central section of the analyzer nuclei, where the electrical response (evoked potential) first appeared, disturbances in the region of the central nuclei lead to a violation of sensations.

2. The secondary zone lies in the environment of the nucleus, is not associated with receptors, the impulse comes through the intercalary neurons from the primary projection zone. Here, a relationship is established between phenomena and their qualities, violations lead to a violation of perceptions (generalized reflections).

3. The tertiary (associative) zone has multisensory neurons. The information has been revised to meaningful. The system is capable of plastic restructuring, long-term storage of traces of sensory action. In case of violation, the form of abstract reflection of reality, speech, purposeful behavior suffer.

Collaboration of the cerebral hemispheres and their asymmetry.

There are morphological prerequisites for the joint work of the hemispheres. The corpus callosum provides a horizontal connection with the subcortical formations and the reticular formation of the brain stem. Thus, the friendly work of the hemispheres and reciprocal innervation are carried out during joint work.

Functional asymmetry. The left hemisphere is dominated by speech, motor, visual and auditory functions. The thinking type of the nervous system is left-hemisphere, and the artistic type is right-hemisphere.

LECTURE No. 8. Physiology of the autonomic nervous system

1. Anatomical and physiological features of the autonomic nervous system

The concept of autonomic nervous system was introduced in 1801 by the French physician A. Besha. This department of the central nervous system provides extraorganic and intraorganic regulation of body functions and includes three components:

1) sympathetic;

2) parasympathetic;

3) metsympathetic.

The autonomic nervous system has a number of anatomical and physiological features that determine the mechanisms of its work.

Anatomical properties

1. Three-component focal arrangement of nerve centers. The lowest level of the sympathetic section is represented by the lateral horns from the VII cervical to III-IV lumbar vertebrae, and the parasympathetic - by the sacral segments and the brain stem. The higher subcortical centers are located on the border of the nuclei of the hypothalamus (the sympathetic division is the posterior group, and the parasympathetic division is the anterior one). The cortical level lies in the region of the sixth-eighth Brodmann fields (motosensory zone), in which point localization of incoming nerve impulses is achieved. Due to the presence of such a structure of the autonomic nervous system, the work of internal organs does not reach the threshold of our consciousness.

2. The presence of autonomic ganglia. In the sympathetic department, they are located either on both sides along the spine, or are part of the plexus. Thus, the arch has a short preganglionic and a long postganglionic path. The neurons of the parasympathetic department are located near the working organ or in its wall, so the arc has a long preganglionic and short postganglionic path.

3. Effetor fibers belong to group B and C.

Physiological properties

1. Features of the functioning of the autonomic ganglia. The presence of the phenomenon of animation (the simultaneous occurrence of two opposite processes - divergence and convergence). Divergence is the divergence of nerve impulses from the body of one neuron to several postganglionic fibers of another. Convergence is the convergence on the body of each postganglionic neuron of impulses from several preganglionic ones. This ensures the reliability of the transfer of information from the central nervous system to the working organ. An increase in the duration of the postsynaptic potential, the presence of trace hyperpolarization and synoptic delay contribute to the transmission of excitation at a speed of 1,5-3,0 m/s. However, the impulses are partially extinguished or completely blocked in the autonomic ganglia. In this way they regulate the flow of information from the central nervous system. Due to this property, they are called nerve centers located on the periphery, and the autonomic nervous system is called autonomous.

2. Features of nerve fibers. Preganglionic nerve fibers belong to group B and conduct excitation at a speed of 3-18 m/s, postganglionic nerve fibers belong to group C. They conduct excitation at a speed of 0,5-3,0 m/s. Since the efferent pathway of the sympathetic department is represented by preganglionic fibers, and the parasympathetic one is represented by postganglionic fibers, the speed of impulse transmission is higher in the parasympathetic nervous system.

Thus, the autonomic nervous system functions differently, its work depends on the characteristics of the ganglia and the structure of the fibers.

2. Functions of the sympathetic, parasympathetic and metsympathetic types of the nervous system

Sympathetic nervous system carries out the innervation of all organs and tissues (stimulates the work of the heart, increases the lumen of the respiratory tract, inhibits the secretory, motor and absorption activity of the gastrointestinal tract, etc.). It performs homeostatic and adaptive-trophic functions.

Its homeostatic role is to maintain the constancy of the internal environment of the body in an active state, i.e.

the sympathetic nervous system is included in the work only during physical exertion, emotional reactions, stress, pain effects, blood loss.

The adaptive-trophic function is aimed at regulating the intensity of metabolic processes. This ensures the adaptation of the organism to the changing conditions of the environment of existence.

Thus, the sympathetic department begins to act in an active state and ensures the functioning of organs and tissues.

Parasympathetic nervous system is a sympathetic antagonist and performs homeostatic and protective functions, regulates the emptying of hollow organs.

The homeostatic role is restorative and operates at rest. This manifests itself in the form of a decrease in the frequency and strength of heart contractions, stimulation of the activity of the gastrointestinal tract with a decrease in blood glucose levels, etc.

All protective reflexes rid the body of foreign particles. For example, coughing clears the throat, sneezing clears the nasal passages, vomiting causes food to be expelled, etc.

Emptying of hollow organs occurs with an increase in the tone of smooth muscles that make up the wall. This leads to the entry of nerve impulses into the central nervous system, where they are processed and sent along the effector path to the sphincters, causing them to relax.

Metsympathetic nervous system is a collection of microganglia located in organ tissue. They consist of three types of nerve cells - afferent, efferent and intercalary, therefore they perform the following functions:

1) provides intraorganic innervation;

2) are an intermediate link between the tissue and the extraorganic nervous system. Under the action of a weak stimulus, the metsympathetic department is activated, and everything is decided at the local level. When strong impulses are received, they are transmitted through the parasympathetic and sympathetic divisions to the central ganglia, where they are processed.

The metsympathetic nervous system regulates the work of smooth muscles that are part of most organs of the gastrointestinal tract, myocardium, secretory activity, local immunological reactions, etc.

LECTURE No. 9. Physiology of the endocrine system. The concept of endocrine glands and hormones, their classification

1. General ideas about the endocrine glands

Endocrine glands - specialized organs that do not have excretory ducts and secrete into the blood, cerebral fluid, lymph through the intercellular gaps.

The endocrine glands are distinguished by a complex morphological structure with good blood supply, located in various parts of the body. A feature of the vessels that feed the glands is their high permeability, which contributes to the easy penetration of hormones into the intercellular gaps, and vice versa. The glands are rich in receptors and are innervated by the autonomic nervous system.

There are two groups of endocrine glands:

1) carrying out external and internal secretion with a mixed function (i.e., these are the sex glands, pancreas);

2) carrying out only internal secretion.

Endocrine cells are also present in some organs and tissues (kidneys, heart muscle, autonomic ganglia, forming a diffuse endocrine system).

A common function for all glands is the production of hormones.

Endocrine function - a complexly organized system consisting of a number of interconnected and finely balanced components. This system is specific and includes:

1) synthesis and secretion of hormones;

2) transport of hormones into the blood;

3) metabolism of hormones and their excretion;

4) the interaction of the hormone with tissues;

5) processes of regulation of gland functions.

Hormones - chemical compounds with high biological activity and in small quantities a significant physiological effect.

Hormones are transported by blood to organs and tissues, while only a small part of them circulates in free active form. The main part is in the blood in bound form in the form of reversible complexes with blood plasma proteins and formed elements. These two forms are in equilibrium with each other, with the resting equilibrium shifted significantly towards the reversible complexes. Their concentration is 80%, and sometimes more, of the total concentration of this hormone in the blood. The formation of a complex of hormones with proteins is a spontaneous, non-enzymatic, reversible process. The components of the complex are connected to each other by non-covalent, weak bonds.

Hormones that are not bound to transport proteins in the blood have direct access to cells and tissues. Two processes occur in parallel: the implementation of the hormonal effect and the metabolic breakdown of hormones. Metabolic inactivation is important in maintaining hormonal homeostasis. Hormonal catabolism is a mechanism for regulating hormone activity in the body.

According to their chemical nature, hormones are divided into three groups:

1) steroids;

2) polypeptides and proteins with and without a carbohydrate component;

3) amino acids and their derivatives.

All hormones have a relatively short half-life of about 30 minutes. Hormones must be constantly synthesized and secreted, act quickly and be inactivated at a high rate. Only in this case they can work effectively as regulators.

The physiological role of the endocrine glands is associated with their influence on the mechanisms of regulation and integration, adaptation, and maintaining the constancy of the internal environment of the body.

2. Properties of hormones, their mechanism of action

There are three main properties of hormones:

1) the distant nature of the action (the organs and systems on which the hormone acts are located far from the place of its formation);

2) strict specificity of action (response reactions to the action of the hormone are strictly specific and cannot be caused by other biologically active agents);

3) high biological activity (hormones are produced by the glands in small quantities, are effective in very small concentrations, a small part of the hormones circulate in the blood in a free active state).

The action of the hormone on body functions is carried out by two main mechanisms: through the nervous system and humorally, directly on organs and tissues.

Hormones function as chemical messengers that carry information or a signal to a specific location - a target cell that has a highly specialized protein receptor to which the hormone binds.

According to the mechanism of action of cells with hormones, hormones are divided into two types.

The first type (steroids, thyroid hormones) - hormones relatively easily penetrate into the cell through plasma membranes and do not require the action of an intermediary (mediator).

The second type - penetrate poorly into the cell, act from its surface, require the presence of a mediator, their characteristic feature is rapidly occurring responses.

In accordance with the two types of hormones, two types of hormonal reception are also distinguished: intracellular (the receptor apparatus is localized inside the cell), membrane (contact) - on its outer surface. Cell receptors - special sections of the cell membrane that form specific complexes with the hormone. Receptors have certain properties, such as:

1) high affinity for a particular hormone;

2) selectivity;

3) limited capacity to the hormone;

4) specificity of localization in the tissue.

These properties characterize the quantitative and qualitative selective fixation of hormones by the cell.

Binding of hormonal compounds by the receptor is a trigger for the formation and release of mediators inside the cell.

The mechanism of action of hormones with the target cell is the following steps:

1) formation of a "hormone-receptor" complex on the membrane surface;

2) activation of membrane adenylcyclase;

3) the formation of cAMP from ATP at the inner surface of the membrane;

4) formation of the "cAMP-receptor" complex;

5) activation of catalytic protein kinase with dissociation of the enzyme into individual units, which leads to protein phosphorylation, stimulation of protein synthesis, RNA synthesis in the nucleus, glycogen breakdown;

6) inactivation of the hormone, cAMP and receptor.

The action of the hormone can be carried out in a more complex way with the participation of the nervous system. Hormones act on interoreceptors that have a specific sensitivity (chemoreceptors in the walls of blood vessels). This is the beginning of a reflex reaction that changes the functional state of the nerve centers. Reflex arcs are closed in various parts of the central nervous system.

There are four types of hormone effects on the body:

1) metabolic effect - effect on metabolism;

2) morphogenetic impact - stimulation of formation, differentiation, growth and metamorphosis;

3) triggering impact - influence on the activity of effectors;

4) corrective effect - a change in the intensity of the activity of organs or the whole organism.

3. Synthesis, secretion and excretion of hormones from the body

Biosynthesis of hormones - a chain of biochemical reactions that form the structure of the hormonal molecule. These reactions occur spontaneously and are genetically fixed in the corresponding endocrine cells. Genetic control is carried out either at the level of formation of mRNA (messenger RNA) of the hormone itself or its precursors (if the hormone is a polypeptide), or at the level of formation of mRNA of enzyme proteins that control various stages of the formation of the hormone (if it is a micromolecule).

Depending on the nature of the hormone being synthesized, there are two types of genetic control of hormonal biogenesis:

1) direct (synthesis of the precursors of most protein-peptide hormones in polysomes), biosynthesis scheme: “genes - mRNA - prohormones - hormones”;

2) mediated (extraribosomal synthesis of steroids, amino acid derivatives and small peptides), scheme:

"genes - (mRNA) - enzymes - hormone".

At the stage of conversion of a prohormone into a hormone of direct synthesis, the second type of control is often connected.

Hormone secretion - the process of release of hormones from endocrine cells into the intercellular gaps with their further entry into the blood, lymph. The secretion of the hormone is strictly specific for each endocrine gland. The secretory process is carried out both at rest and under conditions of stimulation. The secretion of the hormone occurs impulsively, in separate discrete portions. The impulsive nature of hormonal secretion is explained by the cyclic nature of the processes of biosynthesis, deposition and transport of the hormone.

Secretion and biosynthesis of hormones are closely interconnected with each other. This relationship depends on the chemical nature of the hormone and the characteristics of the secretion mechanism. There are three mechanisms of secretion:

1) release from cellular secretory granules (secretion of catecholamines and protein-peptide hormones);

2) release from the protein-bound form (secretion of tropic hormones);

3) relatively free diffusion through cell membranes (secretion of steroids).

The degree of connection between the synthesis and secretion of hormones increases from the first type to the third.

Hormones, entering the blood, are transported to organs and tissues. The hormone associated with plasma proteins and formed elements accumulates in the bloodstream, is temporarily switched off from the circle of biological action and metabolic transformations. An inactive hormone is easily activated and gains access to cells and tissues. In parallel, there are two processes: the implementation of the hormonal effect and metabolic inactivation.

In the process of metabolism, hormones change functionally and structurally. The vast majority of hormones are metabolized, and only a small part (0,5-10%) is excreted unchanged. Metabolic inactivation occurs most intensively in the liver, small intestine and kidneys. The products of hormonal metabolism are actively excreted in the urine and bile, the bile components are finally excreted by the feces through the intestines. A small part of the hormonal metabolites is excreted in sweat and saliva.

4. Regulation of the activity of the endocrine glands

All processes occurring in the body have specific regulatory mechanisms. One of the levels of regulation is intracellular, acting at the cellular level. Like many multi-stage biochemical reactions, the processes of activity of the endocrine glands are to one degree or another self-regulated according to the feedback principle. According to this principle, the previous stage of a chain of reactions either inhibits or enhances subsequent ones. This regulatory mechanism has narrow limits and is able to provide a slightly varying initial level of gland activity.

The primary role in the regulatory mechanism is played by the intercellular systemic control mechanism, which makes the functional activity of the glands dependent on the state of the whole organism. The systemic mechanism of regulation determines the main physiological role of the endocrine glands - bringing the level and ratio of metabolic processes into line with the needs of the whole organism.

Violation of regulatory processes leads to pathology of the functions of the glands and the whole organism as a whole.

Regulatory mechanisms can be stimulating (facilitating) and inhibitory.

The leading place in the regulation of the endocrine glands belongs to the central nervous system. There are several regulatory mechanisms:

1) nervous. Direct nerve influences play a decisive role in the functioning of the innervated organs (adrenal medulla, neuroendocrine zones of the hypothalamus and epiphysis);

2) neuroendocrine, associated with the activity of the pituitary gland and hypothalamus.

In the hypothalamus, the nerve impulse is transformed into a specific endocrine process, leading to the synthesis of the hormone and its release in special zones of neurovascular contact. There are two types of neuroendocrine reactions:

a) the formation and secretion of releasing factors - the main regulators of the secretion of pituitary hormones (hormones are formed in the small cell nuclei of the hypothalamic region, enter the median eminence, where they accumulate and penetrate the adenohypophysis portal circulation system and regulate their functions);

b) the formation of neurohypophyseal hormones (hormones themselves are formed in the large cell nuclei of the anterior hypothalamus, descend to the posterior lobe, where they are deposited, from there they enter the general circulation system and act on peripheral organs);

3) endocrine (the direct effect of some hormones on the biosynthesis and secretion of others (tropic hormones of the anterior pituitary gland, insulin, somatostatin));

4) neuroendocrine humoral. It is carried out by non-hormonal metabolites that have a regulatory effect on the glands (glucose, amino acids, potassium and sodium ions, prostaglandins).

LECTURE No. 10. Characteristics of individual hormones

1. Anterior pituitary hormones

The pituitary gland occupies a special position in the system of endocrine glands. It is called the central gland, since its tropic hormones regulate the activity of other endocrine glands. The pituitary gland is a complex organ; it consists of the adenohypophysis (anterior and middle lobes) and the neurohypophysis (posterior lobe). Hormones of the anterior pituitary gland are divided into two groups: growth hormone and prolactin and tropic hormones (thyrotropin, corticotropin, gonadotropin).

The first group includes somatotropin and prolactin.

Growth hormone (somatotropin) takes part in the regulation of growth, enhancing protein formation. Its most pronounced effect is on the growth of epiphyseal cartilage of the extremities; bone growth increases in length. Violation of the somatotropic function of the pituitary gland leads to various changes in the growth and development of the human body: if there is hyperfunction in childhood, then gigantism develops; with hypofunction - dwarfism. Hyperfunction in an adult does not affect overall growth, but the size of those parts of the body that are still capable of growing increases (acromegaly).

Prolactin promotes the formation of milk in the alveoli, but after prior exposure to female sex hormones (progesterone and estrogen). After childbirth, prolactin synthesis increases and lactation occurs. The act of sucking through a neuroreflex mechanism stimulates the release of prolactin. Prolactin has a luteotropic effect, contributes to the long-term functioning of the corpus luteum and the production of progesterone by it. The second group of hormones include:

1) thyroid-stimulating hormone (thyrotropin). Selectively acts on the thyroid gland, increases its function. With reduced production of thyrotropin, atrophy of the thyroid gland occurs, with overproduction - proliferation, histological changes occur that indicate an increase in its activity;

2) adrenocorticotropic hormone (corticotropin). Stimulates production glucocorticoids adrenal glands. Corticotropin causes breakdown and inhibits protein synthesis, is a growth hormone antagonist. It inhibits the development of the basic substance of connective tissue, reduces the number of mast cells, inhibits the enzyme hyaluronidase, reducing capillary permeability. This determines its anti-inflammatory effect. Under the influence of corticotropin, the size and mass of lymphoid organs decrease. The secretion of corticotropin is subject to diurnal fluctuations: in the evening, its content is higher than in the morning;

3) gonadotropic hormones (gonadotropins - follitropin and lutropin). Present in both women and men;

a) follitropin (follicle-stimulating hormone), which stimulates the growth and development of the follicle in the ovary. It slightly affects the production of estrogen in women, in men, under its influence, spermatozoa are formed;

b) luteinizing hormone (lutropin), which stimulates the growth and ovulation of the follicle with the formation of the corpus luteum. It stimulates the formation of female sex hormones - estrogens. Lutropin promotes the production of androgens in men.

2. Hormones of the middle and posterior lobes of the pituitary gland

The middle lobe of the pituitary gland produces the hormone melanotropin (intermedin), which affects the pigment metabolism.

The posterior pituitary is closely related to the supraoptic and paraventricular nuclei of the hypothalamus. The nerve cells of these nuclei produce neurosecretion, which is transported to the posterior pituitary gland. Hormones accumulate in pituicites, in these cells the hormones are converted into an active form. In the nerve cells of the paraventricular nucleus, oxytocin, in the neurons of the supraoptic nucleus - vasopressin.

Vasopressin performs two functions:

1) enhances the contraction of vascular smooth muscles (the tone of the arterioles increases with a subsequent increase in blood pressure);

2) inhibits the formation of urine in the kidneys (antidiuretic action). The antidiuretic effect is provided by the ability of vasopressin to enhance the reabsorption of water from the tubules of the kidneys into the blood. A decrease in the formation of vasopressin is the cause of diabetes insipidus (diabetes insipidus).

Oxytocin (cytocin) selectively acts on the smooth muscles of the uterus, enhances its contraction. The contraction of the uterus increases dramatically if it was under the influence of estrogen. During pregnancy, oxytocin does not affect the contractility of the uterus, since the corpus luteum hormone progesterone makes it insensitive to all stimuli. Oxytocin stimulates the secretion of milk, it is the excretory function that is enhanced, and not its secretion. Special cells of the mammary gland selectively respond to oxytocin. The act of sucking reflexively promotes the release of oxytocin from the neurohypophysis.

Hypothalamic regulation of pituitary hormone production

Neurons of the hypothalamus produce neurosecretion. Neurosecretion products that contribute to the formation of hormones of the anterior pituitary gland are called liberins, and those that inhibit their formation are called statins. The entry of these substances into the anterior pituitary occurs through the blood vessels.

The regulation of the formation of hormones of the anterior pituitary gland is carried out according to the feedback principle. There are two-way relationships between the tropic function of the anterior pituitary gland and peripheral glands: tropic hormones activate peripheral endocrine glands, the latter, depending on their functional state, also affect the production of tropic hormones. Bilateral relationships exist between the anterior pituitary gland and the sex glands, the thyroid gland and the adrenal cortex. These relationships are called "plus-minus" interactions. Tropic hormones stimulate ("plus") the function of peripheral glands, and hormones of peripheral glands suppress ("minus") the production and release of hormones of the anterior pituitary gland. There is an inverse relationship between the hypothalamus and the tropic hormones of the anterior pituitary gland. An increase in the concentration of pituitary hormone in the blood leads to inhibition of neurosecretion in the hypothalamus.

The sympathetic division of the autonomic nervous system enhances the production of tropic hormones, while the parasympathetic division depresses.

3. Hormones of the epiphysis, thymus, parathyroid glands

The epiphysis is located above the superior tubercles of the quadrigemina. The meaning of the epiphysis is extremely controversial. Two compounds have been isolated from its tissue:

1) melatonin (takes part in the regulation of pigment metabolism, inhibits the development of sexual functions in young people and the action of gonadotropic hormones in adults). This is due to the direct action of melatonin on the hypothalamus, where there is a blockade of the release of luliberin, and on the anterior pituitary gland, where it reduces the effect of luliberin on the release of lutropin;

2) glomerulotropin (stimulates the secretion of aldosterone by the adrenal cortex).

Thymus (thymus gland) - a paired lobular organ located in the upper part of the anterior mediastinum. The thymus produces several hormones: thymosin, homeostatic thymus hormone, thymopoietin I, II, thymus humoral factor. They play an important role in the development of immunological protective reactions of the body, stimulating the formation of antibodies. The thymus controls the development and distribution of lymphocytes. The secretion of thymus hormones is regulated by the anterior pituitary gland.

The thymus reaches its maximum development in childhood. After puberty, it begins to atrophy (the gland stimulates the growth of the body and inhibits the development of the reproductive system). There is an assumption that the thymus affects the exchange of Ca ions and nucleic acids.

With an increase in the thymus gland in children, thymic-lymphatic status occurs. In this condition, in addition to an increase in the thymus, proliferation of lymphatic tissue occurs, an increase in the thymus gland is a manifestation of adrenal insufficiency.

The parathyroid glands are a paired organ, they are located on the surface of the thyroid gland. Parathyroid hormone - parathormone (parathyrin). Parathyroid hormone is found in the cells of the gland in the form of a prohormone, the transformation of prohormone into parathyroid hormone occurs in the Golgi complex. From the parathyroid glands, the hormone directly enters the bloodstream.

Parathyroid hormone regulates Ca metabolism in the body and maintains its constant level in the blood. Normally, the Ca content in the blood is 2,25-2,75 mmol/l (9-11 mg%). Skeletal bone tissue is the main depot of Ca in the body. There is a certain relationship between the level of Ca in the blood and its content in bone tissue. Parathyroid hormone enhances bone resorption, which leads to an increase in the release of Ca ions, regulates the processes of deposition and release of Ca salts in the bones. Influencing Ca metabolism, parathyroid hormone simultaneously affects phosphorus metabolism: it reduces the reabsorption of phosphates in the distal tubules of the kidneys, which leads to a decrease in their concentration in the blood.

Removal of the parathyroid glands leads to lethargy, vomiting, loss of appetite, to scattered contractions of individual muscle groups, which can turn into a prolonged tetanic contraction. The regulation of the activity of the parathyroid glands is determined by the level of Ca in the blood. If the concentration of Ca increases in the blood, this leads to a decrease in the functional activity of the parathyroid glands. With a decrease in the level of Ca, the hormone-forming function of the glands increases.

4. Thyroid hormones. iodinated hormones. thyrocalcitonin. Thyroid dysfunction

The thyroid gland is located on both sides of the trachea below the thyroid cartilage and has a lobular structure. The structural unit is a follicle filled with colloid, where the iodine-containing protein - thyroglobulin - is located.

Thyroid hormones are divided into two groups:

1) iodized - thyroxine, triiodothyronine;

2) thyrocalcitonin (calcitonin).

Iodized hormones are formed in the follicles of the glandular tissue, its formation occurs in three stages:

1) colloid formation, thyroglobulin synthesis;

2) iodination of the colloid, iodine entry into the body, absorption in the form of iodides. Iodides are absorbed by the thyroid gland, oxidized into elemental iodine and included in thyroglobulin, the process is stimulated by the enzyme thyroid peroxycase;

3) release into the bloodstream occurs after hydrolysis of thyroglobulin under the action of cathepsin, which releases active hormones - thyroxine, triiodothyronine.

The main active thyroid hormone is thyroxine, the ratio of thyroxine and triiodothyronine is 4: 1. Both hormones are in the blood in an inactive state, they are associated with proteins of the globulin fraction and plasma albumin. Thyroxine binds more easily to blood proteins, therefore it penetrates the cell faster and has greater biological activity. Liver cells capture hormones, in the liver hormones form compounds with glucuronic acid, which do not have hormonal activity and are excreted in the bile in the gastrointestinal tract. This process is called detoxification, it prevents excessive saturation of the blood with hormones.

The role of iodinated hormones:

1) influence on the functions of the central nervous system. Hypofunction leads to a sharp decrease in motor excitability, weakening of active and defensive reactions;

2) influence on higher nervous activity. They are included in the process of developing conditioned reflexes, differentiation of inhibition processes;

3) impact on growth and development. Stimulate the growth and development of the skeleton, gonads;

4) influence on metabolism. There is an impact on the metabolism of proteins, fats, carbohydrates, mineral metabolism. Strengthening energy processes and an increase in oxidative processes lead to an increase in glucose consumption by tissues, which significantly reduces fat and glycogen stores in the liver;

5) influence on the vegetative system. The number of heartbeats, respiratory movements increases, sweating increases;

6) influence on the blood coagulation system. They reduce the ability of blood to clot (reduce the formation of blood clotting factors), increase its fibrinolytic activity (increase the synthesis of anticoagulants). Thyroxine inhibits the functional properties of platelets - adhesion and aggregation.

Regulation of the formation of iodine-containing hormones is carried out:

1) thyrotropin of the anterior pituitary gland. Affects all stages of iodination, the connection between hormones is carried out according to the type of direct and feedback;

2) iodine. Small doses stimulate the formation of the hormone by enhancing the secretion of follicles, large doses inhibit it;

3) autonomic nervous system: sympathetic - increases the activity of hormone production, parasympathetic - decreases;

4) hypothalamus. Thyreoliberin of the hypothalamus stimulates the pituitary thyrotropin, which stimulates the production of hormones, the connection is carried out by the type of feedback;

5) reticular formation (excitation of its structures increases the production of hormones);

6) the cerebral cortex. Decortication activates the function of the gland initially, decreases significantly over time.

Thyrocalcitocin It is formed by parafollicular cells of the thyroid gland, which are located outside the glandular follicles. It takes part in the regulation of calcium metabolism, under its influence the level of Ca decreases. Thyrocalcitocin lowers the phosphate content in the peripheral blood.

Thyrocalcitocin inhibits the release of Ca ions from bone tissue and increases its deposition in it. It blocks the function of osteoclasts, which destroy bone tissue, and triggers the activation mechanism of osteoblasts involved in the formation of bone tissue.

The decrease in the content of Ca and phosphate ions in the blood is due to the effect of the hormone on the excretory function of the kidneys, reducing the tubular reabsorption of these ions. The hormone stimulates the absorption of Ca ions by mitochondria.

The regulation of thyrocalcitonin secretion depends on the level of Ca ions in the blood: an increase in its concentration leads to degranulation of parafollicles. Active secretion in response to hypercalcemia maintains the concentration of Ca ions at a certain physiological level.

The secretion of thyrocalcitonin is promoted by some biologically active substances: gastrin, glucagon, cholecystokinin.

With the excitation of beta-adrenergic receptors, the secretion of the hormone increases, and vice versa.

Dysfunction of the thyroid gland is accompanied by an increase or decrease in its hormone-forming function.

Insufficiency of hormone production (hypothyroidism), which appears in childhood, leads to the development of cretinism (growth, sexual development, mental development are delayed, there is a violation of body proportions).

Lack of hormone production leads to the development of myxedema, which is characterized by a sharp disorder in the processes of excitation and inhibition in the central nervous system, mental retardation, decreased intelligence, lethargy, drowsiness, sexual dysfunction, and inhibition of all types of metabolism.

When the thyroid gland is overactive (hyperthyroidism), disease occurs thyrotoxicosis. Characteristic signs: an increase in the size of the thyroid gland, the number of heartbeats, an increase in metabolism, body temperature, an increase in food intake, bulging eyes. Increased excitability and irritability are observed, the ratio of the tone of the sections of the autonomic nervous system changes: excitation of the sympathetic section predominates. Muscle tremor and muscle weakness are noted.

A lack of iodine in water leads to a decrease in the function of the thyroid gland with a significant proliferation of its tissue and the formation of a goiter. Tissue proliferation is a compensatory mechanism in response to a decrease in the content of iodinated hormones in the blood.

5. Pancreatic hormones. Pancreatic dysfunction

The pancreas is a gland with mixed function. The morphological unit of the gland is the islets of Langerhans; they are mainly located in the tail of the gland. Beta cells of the islets produce insulin, alpha cells produce glucagon, and delta cells produce somatostatin. The hormones vagotonin and centropnein were found in pancreatic tissue extracts.

Insulin regulates carbohydrate metabolism, reduces the concentration of sugar in the blood, promotes the conversion of glucose into glycogen in the liver and muscles. It increases the permeability of cell membranes for glucose: once inside the cell, glucose is absorbed. Insulin delays the breakdown of proteins and their conversion into glucose, stimulates protein synthesis from amino acids and their active transport into the cell, regulates fat metabolism by forming higher fatty acids from carbohydrate metabolism products, and inhibits the mobilization of fat from adipose tissue.

In beta cells, insulin is produced from its precursor, proinsulin. It is transferred to the Golgi cell apparatus, where the initial stages of the conversion of proinsulin to insulin take place.

Insulin regulation is based on the normal content of glucose in the blood: hyperglycemia leads to an increase in the flow of insulin into the blood, and vice versa.

The paraventricular nuclei of the hypothalamus increase activity during hyperglycemia, excitation goes to the medulla oblongata, from there to the pancreatic ganglion and to beta cells, which enhances the formation of insulin and its secretion. With hypoglycemia, the nuclei of the hypothalamus reduce their activity, and insulin secretion decreases.

Hyperglycemia directly excites the receptor apparatus of the islets of Langerhans, which increases insulin secretion. Glucose also acts directly on beta cells, leading to the release of insulin.

Glucagon increases the amount of glucose, which also leads to increased insulin production. The adrenal hormones work in a similar way.

The autonomic nervous system regulates insulin production through the vagus and sympathetic nerves. The vagus nerve stimulates insulin release, while the sympathetic nerve inhibits it.

The amount of insulin in the blood is determined by the activity of the enzyme insulinase, which destroys the hormone. The largest amount of the enzyme is found in the liver and muscles. With a single flow of blood through the liver, up to 50% of the insulin in the blood is destroyed.

An important role in the regulation of insulin secretion is played by the hormone somatostatin, which is formed in the nuclei of the hypothalamus and delta cells of the pancreas. Somatostatin inhibits insulin secretion.

Insulin activity is expressed in laboratory and clinical units.

Glucagon is involved in the regulation of carbohydrate metabolism; by its action on carbohydrate metabolism, it is an insulin antagonist. Glucagon breaks down glycogen in the liver to glucose, which raises blood glucose levels. Glucagon stimulates the breakdown of fats in adipose tissue.

The mechanism of action of glucagon is due to its interaction with special specific receptors that are located on the cell membrane. When glucagon binds to them, the activity of the enzyme adenylate cyclase and the concentration of cAMP increase, cAMP promotes the process of glycogenolysis.

Regulation of glucagon secretion. The formation of glucagon in alpha cells is influenced by the level of glucose in the blood. When blood glucose increases, glucagon secretion is inhibited, and when it decreases, it increases. The formation of glucagon is also influenced by the anterior lobe of the pituitary gland.

A growth hormone somatotropin increases alpha cell activity. In contrast, the delta cell hormone somatostatin inhibits the formation and secretion of glucagon, since it blocks the entry of Ca ions into alpha cells, which are necessary for the formation and secretion of glucagon.

Physiological significance lipocaine. It promotes the utilization of fats by stimulating the formation of lipids and the oxidation of fatty acids in the liver, it prevents fatty degeneration of the liver.

Functions vagotonin - increased tone of the vagus nerves, increased their activity.

Functions centropnein - excitation of the respiratory center, promoting relaxation of the smooth muscles of the bronchi, increasing the ability of hemoglobin to bind oxygen, improving oxygen transport.

Violation of the function of the pancreas.

A decrease in insulin secretion leads to the development of diabetes mellitus, the main symptoms of which are hyperglycemia, glucosuria, polyuria (up to 10 liters per day), polyphagia (increased appetite), polydyspepsia (increased thirst).

An increase in blood sugar in diabetic patients is the result of a loss in the ability of the liver to synthesize glycogen from glucose, and cells to utilize glucose. In the muscles, the process of formation and deposition of glycogen also slows down.

In diabetic patients, all types of metabolism are disturbed.

6. Adrenal hormones. Glucocorticoids

The adrenal glands are paired glands located above the upper poles of the kidneys. They are of vital importance. There are two types of hormones: cortical hormones and medulla hormones.

The hormones of the cortical layer last into three groups:

1) glucocorticoids (hydrocortisone, cortisone, corticosterone);

2) mineralocorticoids (aldesterone, deoxycorticosterone);

3) sex hormones (androgens, estrogens, progesterone).

Glucocorticoids are synthesized in the zona fasciculata of the adrenal cortex. According to the chemical structure, hormones are steroids, they are formed from cholesterol, ascorbic acid is necessary for synthesis.

Physiological significance of glucocorticoids.

Glucocorticoids affect the metabolism of carbohydrates, proteins and fats, enhance the formation of glucose from proteins, increase the deposition of glycogen in the liver, and are insulin antagonists in their action.

Glucocorticoids have a catabolic effect on protein metabolism, cause tissue protein breakdown and delay the incorporation of amino acids into proteins.

Hormones have an anti-inflammatory effect, which is due to a decrease in the permeability of the vessel walls with a low activity of the hyaluronidase enzyme. The decrease in inflammation is due to the inhibition of the release of arachidonic acid from phospholipids. This leads to a restriction of the synthesis of prostaglandins, which stimulate the inflammatory process.

Glucocorticoids affect the production of protective antibodies: hydrocortisone inhibits the synthesis of antibodies, inhibits the reaction of the interaction of an antibody with an antigen.

Glucocorticoids have a pronounced effect on the hematopoietic organs:

1) increase the number of red blood cells by stimulating the red bone marrow;

2) lead to the reverse development of the thymus and lymphoid tissue, which is accompanied by a decrease in the number of lymphocytes.

Excretion from the body is carried out in two ways:

1) 75-90% of the hormones that enter the blood are removed with urine;

2) 10-25% is removed with feces and bile.

Regulation of the formation of glucocorticoids.

An important role in the formation of glucocorticoids is played by corticotropin of the anterior pituitary gland. This effect is carried out according to the principle of direct and feedback: corticotropin increases the production of glucocorticoids, and their excessive content in the blood leads to inhibition of corticotropin in the pituitary gland.

Neurosecretion is synthesized in the nuclei of the anterior hypothalamus corticoliberin, which stimulates the formation of corticotropin in the anterior pituitary gland, and it, in turn, stimulates the formation of glucocorticoid. The functional relationship "hypothalamus - anterior pituitary gland - adrenal cortex" is located in a single hypothalamic-pituitary-adrenal system, which plays a leading role in the body's adaptive reactions.

Adrenaline - the hormone of the adrenal medulla - enhances the formation of glucocorticoids.

7. Adrenal hormones. Mineralocorticoids. sex hormones

Mineralocorticoids are formed in the glomerular zone of the adrenal cortex and take part in the regulation of mineral metabolism. These include aldosterone и deoxycorticosterone. They increase the reabsorption of Na ions in the renal tubules and reduce the reabsorption of K ions, which leads to an increase in Na ions in the blood and tissue fluid and an increase in their osmotic pressure. This causes water retention in the body and an increase in blood pressure.

Mineralocorticoids contribute to the manifestation of inflammatory reactions by increasing the permeability of capillaries and serous membranes. They take part in the regulation of the tone of blood vessels. Aldosterone has the ability to increase the tone of the smooth muscles of the vascular wall, which leads to an increase in blood pressure. With a lack of aldosterone, hypotension develops.

Regulation of mineralocorticoid formation

The secretion and formation of aldosterone is regulated by the renin-angiotensin system. Renin is formed in special cells of the juxtaglomerular apparatus of the afferent arterioles of the kidney and is released into the blood and lymph. It catalyzes the conversion of angiotensinogen to angiotensin I, which is converted under the action of a special enzyme to angiotensin II. Angiotensin II stimulates the formation of aldosterone. The synthesis of mineralocorticoids is controlled by the concentration of Na and K ions in the blood. An increase in Na ions leads to inhibition of aldosterone secretion, which leads to the excretion of Na in the urine. A decrease in the formation of mineralocorticoids occurs with an insufficient content of K ions. The amount of tissue fluid and blood plasma affects the synthesis of mineralocorticoids. An increase in their volume leads to inhibition of aldosterone secretion, which is due to increased release of Na ions and water associated with it. The pineal hormone glomerulotropin enhances the synthesis of aldosterone.

sex hormones (androgens, estrogens, progesterone) are formed in the reticular zone of the adrenal cortex. They are of great importance in the development of the genital organs in childhood, when the intrasecretory function of the sex glands is negligible. They have an anabolic effect on protein metabolism: they increase protein synthesis due to the increased inclusion of amino acids in its molecule.

With hypofunction of the adrenal cortex, a disease occurs - bronze disease, or Addison's disease. Signs of this disease are: bronze coloration of the skin, especially on the hands, neck, face, fatigue, loss of appetite, nausea and vomiting. The patient becomes sensitive to pain and cold, more susceptible to infection.

With hyperfunction of the adrenal cortex (the cause of which is most often a tumor), there is an increase in the formation of hormones, a predominance of the synthesis of sex hormones over others is noted, so secondary sexual characteristics begin to change dramatically in patients. In women, the manifestation of secondary male sexual characteristics is observed, in men - female ones.

8. Hormones of the adrenal medulla

The adrenal medulla produces hormones related to catecholamines. The main hormone is adrenalin, the second most important is the precursor of adrenaline - norepinephrine. Chromaffin cells of the adrenal medulla are also found in other parts of the body (on the aorta, at the junction of the carotid arteries, etc.), they form the adrenal system of the body. The adrenal medulla is a modified sympathetic ganglion.

Significance of adrenaline and norepinephrine

Adrenaline performs the function of a hormone, it enters the blood constantly, under various conditions of the body (blood loss, stress, muscle activity), its formation and release into the blood increase.

Excitation of the sympathetic nervous system leads to an increase in the flow of adrenaline and norepinephrine into the blood, they lengthen the effects of nerve impulses in the sympathetic nervous system. Adrenaline affects carbon metabolism, accelerates the breakdown of glycogen in the liver and muscles, relaxes bronchial muscles, inhibits gastrointestinal motility and increases the tone of its sphincters, increases the excitability and contractility of the heart muscle. It increases the tone of blood vessels, acts as a vasodilator on the vessels of the heart, lungs and brain. Adrenaline enhances the performance of skeletal muscles.

An increase in the activity of the adrenal system occurs under the influence of various stimuli that cause a change in the internal environment of the body. Adrenaline blocks these changes.

Adrenaline is a hormone with a short duration of action, it is rapidly destroyed by monoamine oxidase. This is in full accordance with the fine and precise central regulation of the secretion of this hormone for the development of adaptive and protective reactions of the body.

Norepinephrine performs the function of a mediator, it is part of sympathin, a mediator of the sympathetic nervous system, it takes part in the transmission of excitation in CNS neurons.

The secretory activity of the adrenal medulla is regulated by the hypothalamus, in the posterior group of its nuclei are the higher autonomic centers of the sympathetic division. Their activation leads to an increase in the release of adrenaline into the blood. The release of adrenaline can occur reflexively during hypothermia, muscle work, etc. With hypoglycemia, the release of adrenaline into the blood reflexively increases.

9. Sex hormones. Menstrual cycle

The sex glands (testes in men, ovaries in women) are glands with a mixed function, the intrasecretory function is manifested in the formation and secretion of sex hormones that directly enter the bloodstream.

Male sex hormones - androgens are formed in the interstitial cells of the testes. There are two types of androgens - testosterone и androsterone.

Androgens stimulate the growth and development of the reproductive apparatus, male sexual characteristics and the appearance of sexual reflexes.

They control the process of maturation of spermatozoa, contribute to the preservation of their motor activity, the manifestation of sexual instinct and sexual behavioral reactions, increase the formation of protein, especially in muscles, and reduce body fat. With an insufficient amount of androgen in the body, the processes of inhibition in the cerebral cortex are disrupted.

Female sex hormones estrogens are formed in the follicles of the ovary. The synthesis of estrogen is carried out by the follicle membrane, progesterone - by the corpus luteum of the ovary, which develops at the site of the burst follicle.

Estrogens stimulate the growth of the uterus, vagina, tubes, cause the growth of the endometrium, promote the development of secondary female sexual characteristics, the manifestation of sexual reflexes, increase the contractility of the uterus, increase its sensitivity to oxytocin, stimulate the growth and development of the mammary glands.

Progesterone ensures the normal course of pregnancy, promotes the growth of the endometrial mucosa, implantation of a fertilized egg into the endometrium, inhibits the contractility of the uterus, reduces its sensitivity to oxytocin, inhibits the maturation and ovulation of the follicle by inhibiting the formation of pituitary lutropin.

The formation of sex hormones is influenced by the gonadotropic hormones of the pituitary gland and prolactin. In men, gonadotropic hormone promotes the maturation of sperm, in women - the growth and development of the follicle. Lutropin determines the production of female and male sex hormones, ovulation and the formation of the corpus luteum. Prolactin stimulates the production of progesterone.

Melatonin inhibits the activity of the sex glands.

The nervous system takes part in the regulation of the activity of the sex glands due to the formation of gonadotropic hormones in the pituitary gland. The central nervous system regulates the course of sexual intercourse. With a change in the functional state of the central nervous system, a violation of the sexual cycle and even its termination may occur.

The menstrual cycle includes four periods.

1. Pre-ovulation (from the fifth to the fourteenth day). The changes are caused by the action of follitropin, increased formation of estrogens occurs in the ovaries, they stimulate the growth of the uterus, the proliferation of the mucous membrane and its glands, the maturation of the follicle accelerates, its surface ruptures, and an egg is released from it - ovulation occurs.

2. Ovulation (from the fifteenth to the twenty-eighth day). It begins with the release of the egg into the tube, the contraction of the smooth muscles of the tube helps to move it to the uterus, fertilization can occur here. A fertilized egg, getting into the uterus, is attached to its mucous membrane and pregnancy occurs. If fertilization does not occur, the post-ovulation period begins. In place of the follicle, a corpus luteum develops, it produces progesterone.

3. Post-ovulation period. An unfertilized egg, reaching the uterus, dies. Progesterone reduces the formation of follitropin and reduces the production of estrogens. Changes that have arisen in the genitals of a woman disappear. In parallel, the formation of lutropin decreases, which leads to atrophy of the corpus luteum. Due to a decrease in estrogen, the uterus contracts, and the mucous membrane is shed. In the future, it is regenerated.

4. The rest period and the post-ovulation period last from the first to the fifth day of the sexual cycle.

10. Hormones of the placenta. The concept of tissue hormones and antihormones

The placenta is a unique formation that connects the mother's body with the fetus. It performs numerous functions, including metabolic and hormonal. It synthesizes hormones of two groups:

1) protein - chorionic gonadotropin (CG), placental lactogenic hormone (PLG), relaxin;

2) steroid - progesterone, estrogen.

HCG is formed in large quantities after 7-12 weeks of pregnancy; subsequently, the formation of the hormone decreases several times, its secretion is not controlled by the pituitary gland and hypothalamus, and its transport to the fetus is limited. The functions of hCG are to increase the growth of follicles, the formation of the corpus luteum, and stimulate the production of progesterone. The protective function is the ability to prevent rejection of the embryo by the mother's body. HCG has an antiallergic effect.

PLH begins to be secreted from the sixth week of pregnancy and progressively increases. It affects the mammary glands like pituitary prolactin, protein metabolism (increases protein synthesis in the mother's body). At the same time, the content of free fatty acids increases, and resistance to insulin action increases.

Relaxin is secreted in the later stages of pregnancy, relaxes the ligaments of the pubic symphysis, reduces the tone of the uterus and its contractility.

Progesterone is synthesized by the corpus luteum until the fourth or sixth week of pregnancy, later the placenta is included in this process, the secretion process progressively increases. Progesterone causes uterine relaxation, reduced uterine contractility and sensitivity to estrogen and oxytocin, accumulation of water and electrolytes, especially intracellular sodium. Estrogens and progesterone promote growth, stretching of the uterus, development of the mammary glands and lactation.

Tissue hormones are biologically active substances that act at the site of their formation and do not enter the bloodstream. Prostaglandins are formed in microsomes of all tissues, take part in the regulation of the secretion of digestive juices, changes in the tone of smooth muscles of blood vessels and bronchi, and the process of platelet aggregation. Tissue hormones that regulate local blood circulation include histamine (dilates blood vessels) and serotonin (has a pressor effect). Tissue hormones are considered to be mediators of the nervous system - norepinephrine and acetylcholine.

Antihormones - Substances with antihormonal activity. Their formation occurs with prolonged administration of the hormone into the body from the outside. Each antihormone has a pronounced species specificity and blocks the action of the type of hormone for which it has been produced. It appears in the blood 1-3 months after the administration of the hormone and disappears 3-9 months after the last injection of the hormone.

LECTURE No. 11. Higher nervous activity

1. The concept of higher and lower nervous activity

Lower nervous activity is an integrative function of the spinal and brainstem, which is aimed at the regulation of vegetative-visceral reflexes. With its help, the work of all internal organs and their adequate interaction with each other are ensured.

Higher nervous activity is inherent only in the brain, which controls the individual behavioral reactions of the organism in the environment. In evolutionary terms, this is a newer and more complex function. It has a number of features.

1. The cerebral cortex and subcortical formations (the nuclei of the thalamus, limbic system, hypothalamus, basal nuclei) act as a morphological substrate.

2. Controls contact with the surrounding reality.

3. Instincts and conditioned reflexes underlie the mechanisms of emergence.

Instincts are innate, unconditioned reflexes and represent a set of motor acts and complex forms of behavior (food, sexual, self-preservation). They have features of manifestation and functioning associated with physiological properties:

1) the morphological substrate is the limbic system, basal ganglia, hypothalamus;

2) are of a chain nature, that is, the time of the end of the action of one unconditioned reflex is a stimulus for the beginning of the action of the next;

3) the humoral factor is of great importance for manifestation (for example, for food reflexes - a decrease in blood glucose levels);

4) have ready-made reflex arcs;

5) form the basis for conditioned reflexes;

6) are inherited and have specific character;

7) differ in constancy and change little during life;

8) do not require additional conditions for manifestation, they arise on the action of an adequate stimulus.

Conditional reflexes are produced during life, as they do not have ready-made reflex arcs. They are individual in nature and, depending on the conditions of existence, can constantly change. Their features:

1) the morphological substrate is the cerebral cortex, when it is removed, the old reflexes disappear, and new ones are not developed;

2) on their basis, the interaction of the organism with the external environment is formed, i.e. they clarify, complicate and make these relationships subtle.

So, conditioned reflexes are a set of behavioral reactions acquired during life. Their classification:

1) according to the nature of the conditioned stimulus, natural and artificial reflexes are distinguished. Natural reflexes are developed for the natural qualities of the stimulus (for example, the type of food), and artificial - for any;

2) according to the receptor sign - exteroceptive, interoceptive and proprioceptive;

3) depending on the structure of the conditioned stimulus - simple and complex;

4) along the efferent path - somatic (motor) and autonomic (sympathetic and parasympathetic);

5) according to biological significance - vital (food, defensive, locomotor), zoosocial, indicative;

6) by the nature of the reinforcement - of the lower and higher order;

7) depending on the combination of the conditioned and unconditioned stimulus - cash and trace.

Thus, conditioned reflexes are developed throughout life and are of great importance for a person.

2. Formation of conditioned reflexes

Certain conditions are necessary for the formation of conditioned reflexes.

1. The presence of two stimuli - indifferent and unconditioned. This is due to the fact that an adequate stimulus will cause an unconditioned reflex, and already on its basis a conditioned one will be developed. An indifferent stimulus extinguishes the orienting reflex.

2. A certain combination in time of two stimuli. First, the indifferent must turn on, and then the unconditional, and the intermediate time must be constant.

3. A certain combination of the strength of two stimuli. Indifferent - threshold, and unconditional - superthreshold.

4. The usefulness of the central nervous system.

5. Absence of extraneous irritants.

6. Repeated repetition of the action of stimuli for the emergence of a dominant focus of excitation.

The mechanism of formation of conditioned reflexes is based on the principle of the formation of a temporary nervous connection in the cerebral cortex. I.P. Pavlov believed that a temporary nervous connection is formed between the cerebral part of the analyzer and the cortical representation of the center of the unconditioned reflex according to the dominant mechanism. E. A. Asratyan suggested that a temporary nervous connection is formed between two short branches of two unconditioned reflexes at different levels of the central nervous system according to the dominant principle. P.K. Anokhin based the principle of irradiation of excitation throughout the cerebral cortex due to the convergence of impulses on multimodal neurons. According to modern concepts, the cortex and subcortical formations are involved in this process, since in experiments on animals, when the integrity is violated, conditioned reflexes are practically not developed. Thus, temporary neural connection is the result of integrative activity of the entire brain.

Under experimental conditions, it has been proven that the formation of a conditioned reflex occurs in three stages:

1) acquaintance;

2) the development of a conditioned reflex, after the repayment of the indicative reflex;

3) fixing the developed conditioned reflex.

Fixation occurs in two stages. Initially, a conditioned reflex also occurs to the action of similar stimuli due to the irradiation of excitation. After a short period of time, only to a conditioned signal, since there is a concentration of excitation processes in the projection area in the cerebral cortex.

3. Inhibition of conditioned reflexes. The concept of a dynamic stereotype

This process is based on two mechanisms: unconditional (external) and conditional (internal) inhibition.

Unconditional inhibition occurs instantly due to the cessation of conditioned reflex activity. Allocate external and transcendental braking.

To activate external inhibition, the action of a new strong stimulus is necessary, capable of creating a dominant focus of excitation in the cerebral cortex. As a result, the work of all nerve centers is inhibited, and the temporary nervous connection ceases to function. This type of inhibition causes a rapid switch to a more important biological signal.

Transmarginal inhibition plays a protective role and protects neurons from overexcitation, as it prevents the formation of connections under the action of a superstrong stimulus.

For the occurrence of conditional inhibition, the presence of special conditions (for example, the absence of signal reinforcement) is necessary. There are four types of braking:

1) fading (eliminates unnecessary reflexes due to the lack of their reinforcement);

2) trim (leads to the sorting of close stimuli);

3) delayed (occurs with an increase in the duration of the action between two signals, leads to getting rid of unnecessary reflexes, forms the basis for assessing the balance and balance of the processes of excitation and inhibition in the central nervous system);

4) conditioned inhibitor (manifested only under the action of an additional stimulus of moderate strength, which causes a new focus of excitation and inhibits the rest, is the basis for the processes of training and education).

Inhibition frees the body from unnecessary reflex connections and further complicates the relationship of man with the environment.

dynamic stereotype - developed and fixed system of reflex connections. It consists of an external and an internal component. A certain sequence of conditional and unconditional signals (light, bell, food) is put at the basis of the external. The basis for the internal is the appearance of foci of excitation in the cortex of the cerebral hemispheres (occipital, temporal, frontal lobes, etc.), adequate to this effect. Due to the presence of a dynamic stereotype, the processes of excitation and inhibition proceed more easily, the central nervous system is better prepared to perform other reflex actions.

4. The concept of the types of the nervous system

The type of the nervous system directly depends on the intensity of the processes of inhibition and excitation and the conditions necessary for their production. Type of nervous system is a set of processes occurring in the cerebral cortex. It depends on the genetic predisposition and may vary slightly over the course of an individual's life. The main properties of the nervous process are balance, mobility, strength.

Balance is characterized by the same intensity of the processes of excitation and inhibition in the central nervous system.

Mobility is determined by the rate at which one process is replaced by another. If the process is fast, then the nervous system is mobile, if not, then the system is inactive.

Strength depends on the ability to respond adequately to both strong and super-strong stimuli. If there is excitation, then the nervous system is strong, if inhibition, then it is weak.

According to the intensity of these processes, IP Pavlov identified four types of the nervous system, two of which he called extreme due to weak nervous processes, and two - central.

To characterize each type, I.P. Pavlov proposed using his own classification along with the classification of Hippocrates. According to these data, people with I type nervous system (melancholic) are cowardly, whiny, attach great importance to any trifle, pay increased attention to difficulties, as a result they often have a bad mood and distrust. This is an inhibitory type of nervous system; black bile predominates in the body. For persons II type Characterized by aggressive and emotional behavior, rapid mood changes from anger to mercy, ambition. They are dominated by strong and unbalanced processes, according to Hippocrates - choleric. Sanguine people - type III - are confident leaders, they are energetic and enterprising. Their nervous processes are strong, agile and balanced. Phlegmatic - IV type - quite calm and self-confident, with strong balanced and mobile nervous processes.

In humans, it is not easy to determine the type of nervous system, since the ratio of the cerebral cortex and subcortical formations, the degree of development of signaling systems, and the level of intelligence play an important role.

It has been proven that a person's performance is largely influenced not by the type of nervous system, but by the environment and social factors, since in the process of training and education, moral principles are acquired first of all. In animals, the biological environment plays a major role. So, animals of the same litter, placed in different conditions of existence, will have different types. Thus, the genetically determined type of the nervous system is the basis for the formation of individual characteristics of the phenotype during life.

5. The concept of signaling systems. Stages of formation of signaling systems

Signal system - a set of conditioned reflex connections between the body and the environment, which subsequently serves as the basis for the formation of higher nervous activity. Based on the time of formation, the first and second signaling systems are distinguished. The first signaling system is a complex of reflexes to a specific stimulus, for example to light, sound, etc. It is carried out due to specific receptors that perceive reality in specific images. In this signaling system, sensory organs that transmit excitation to the cerebral cortex play an important role, in addition to the cerebral part of the speech motor analyzer. The second signaling system is formed on the basis of the first and is a conditioned reflex activity in response to a verbal stimulus. It functions through the speech motor, auditory and visual analyzers. Its stimulus is the word, so it gives rise to abstract thinking. The speech motor part of the cerebral cortex acts as a morphological substrate. The second signaling system has a high rate of irradiation and is characterized by the rapid occurrence of excitation and inhibition processes.

The signaling system also affects the type of nervous system.

Types of the nervous system:

1) medium type (there is the same severity);

2) artistic (the first signal system prevails);

3) thinking (the second signal system is developed);

4) artistic and mental (both signal systems are simultaneously expressed).

Four stages are necessary for the formation of signaling systems:

1) the stage at which an immediate response occurs to an immediate stimulus appears during the first month of life;

2) the stage at which a direct response appears to a verbal stimulus occurs in the second half of life;

3) the stage at which a verbal reaction occurs to an immediate stimulus develops at the beginning of the second year of life;

4) the stage at which there is a verbal response to a verbal stimulus, the child understands speech and gives an answer.

To develop signaling systems, you need:

1) the ability to develop conditioned reflexes to a complex of stimuli;

2) the possibility of developing conditioned reflexes;

3) the presence of differentiation of stimuli;

4) the ability to generalize reflex arcs.

Thus, signaling systems are the basis for higher nervous activity.

LECTURE No. 12. Physiology of the heart

1. Components of the circulatory system. Circles of blood circulation

The circulatory system consists of four components: the heart, blood vessels, organs - blood depots, regulation mechanisms.

The circulatory system is a constituent component of the cardiovascular system, which, in addition to the circulatory system, includes the lymphatic system. Due to its presence, a constant continuous movement of blood through the vessels is ensured, which is influenced by a number of factors:

1) the work of the heart as a pump;

2) pressure difference in the cardiovascular system;

3) isolation;

4) valvular apparatus of the heart and veins, which prevents the reverse flow of blood;

5) the elasticity of the vascular wall, especially large arteries, due to which the pulsating ejection of blood from the heart is converted into a continuous current;

6) negative intrapleural pressure (sucks blood and facilitates its venous return to the heart);

7) gravity of blood;

8) muscle activity (the contraction of the skeletal muscles ensures the pushing of blood, while the frequency and depth of breathing increase, which leads to a decrease in pressure in the pleural cavity, an increase in the activity of proprioreceptors, causing excitation in the central nervous system and an increase in the strength and frequency of heart contractions).

In the human body, blood circulates through two circles of blood circulation - large and small, which, together with the heart, form a closed system.

Small circle of blood circulation was first described by M. Servet in 1553. It begins in the right ventricle and continues into the pulmonary trunk, passes into the lungs, where gas exchange takes place, then blood enters the left atrium through the pulmonary veins. The blood is enriched with oxygen. From the left atrium, arterial blood, saturated with oxygen, enters the left ventricle, from where it begins big circle. It was opened in 1685 by W. Harvey. Blood containing oxygen is sent through the aorta through smaller vessels to tissues and organs where gas exchange takes place. As a result, venous blood with a low oxygen content flows through the system of hollow veins (upper and lower), which flow into the right atrium.

A special feature is the fact that in a large circle, arterial blood moves through the arteries, and venous blood through the veins. In a small circle, on the contrary, venous blood flows through the arteries, and arterial blood flows through the veins.

2. Morphofunctional features of the heart

The heart is a four-chambered organ consisting of two atria, two ventricles and two atrial appendages. It is with the contraction of the atria that the work of the heart begins. The weight of the heart in an adult is 0,04% of body weight. Its wall is formed by three layers - endocardium, myocardium and epicardium. The endocardium consists of connective tissue and provides the organ with a non-wetting wall, which facilitates hemodynamics. The myocardium is formed by striated muscle fiber, the greatest thickness of which is in the region of the left ventricle, and the smallest in the atrium. The epicardium is a visceral layer of the serous pericardium, under which blood vessels and nerve fibers are located. Outside the heart is the pericardium - the pericardial sac. It consists of two layers - serous and fibrous. The serous layer is formed by visceral and parietal layers. The parietal layer connects with the fibrous layer and forms the pericardial sac. There is a cavity between the epicardium and the parietal layer, which should normally be filled with serous fluid to reduce friction. Functions of the pericardium:

1) protection against mechanical influences;

2) prevention of overstretching;

3) the basis for large blood vessels.

The heart is divided by a vertical septum into the right and left halves, which in an adult do not normally communicate with each other. The horizontal septum is formed by fibrous fibers and divides the heart into the atrium and ventricles, which are connected by the atrioventricular plate. There are two types of valves in the heart - cuspid and semilunar. The valve is a duplicate of the endocardium, in the layers of which there are connective tissue, muscle elements, blood vessels and nerve fibers.

The leaflet valves are located between the atrium and the ventricle, with three leaflets in the left half and two in the right half. The semilunar valves are located at the point where the blood vessels - the aorta and pulmonary trunk - exit the ventricles. They are equipped with pockets that close when filled with blood. The operation of the valves is passive and is influenced by the pressure difference.

The cycle of cardiac activity consists of systole and diastole. Systole - a contraction that lasts 0,1-0,16 s in the atrium and 0,3-0,36 s in the ventricle. Atrial systole is weaker than ventricular systole. Diastole - relaxation, in the atria it takes 0,7-0,76 s, in the ventricles - 0,47-0,56 s. The duration of the cardiac cycle is 0,8-0,86 s and depends on the frequency of contractions. The time during which the atria and ventricles are at rest is called a general pause in the activity of the heart. It lasts approximately 0,4 s. During this time, the heart rests, and its chambers are partially filled with blood. Systole and diastole are complex phases and consist of several periods. In systole, two periods are distinguished - tension and expulsion of blood, including:

1) phase of asynchronous contraction - 0,05 s;

2) the phase of isometric contraction - 0,03 s;

3) the phase of rapid expulsion of blood - 0,12 s;

4) phase of slow expulsion of blood - 0,13 s.

Diastole lasts about 0,47 s and consists of three periods:

1) protodiastolic - 0,04 s;

2) isometric - 0,08 s;

3) the filling period, in which there is a phase of rapid expulsion of blood - 0,08 s, a phase of slow expulsion of blood - 0,17 s, presystole time - filling of the ventricles with blood - 0,1 s.

The duration of the cardiac cycle is affected by heart rate, age and gender.

3. Myocardial physiology. The conduction system of the myocardium. Properties of atypical myocardium

The myocardium is represented by striated muscle tissue, consisting of individual cells - cardiomyocytes, interconnected by nexuses, and forming the myocardial muscle fiber. Thus, it has no anatomical integrity, but functions as a syncytium. This is due to the presence of nexuses, which ensure rapid conduction of excitation from one cell to the rest. Based on the characteristics of their functioning, two types of muscles are distinguished: working myocardium and atypical muscles.

The working myocardium is formed by muscle fibers with a well-developed striated striation. The working myocardium has a number of physiological properties:

1) excitability;

2) conductivity;

3) low lability;

4) contractility;

5) refractoriness.

Excitability is the ability of a striated muscle to respond to nerve impulses. It is smaller than that of striated skeletal muscles. The cells of the working myocardium have a large membrane potential and, due to this, react only to strong irritation.

Due to the low speed of conduction of excitation, alternate contraction of the atria and ventricles is provided.

The refractory period is quite long and is related to the period of action. The heart can contract as a single muscle contraction (due to a long refractory period) and according to the "all or nothing" law.

Atypical muscle fibers have mild contraction properties and have a fairly high level of metabolic processes. This is due to the presence of mitochondria, which perform a function close to the function of the nervous tissue, i.e., it provides the generation and conduction of nerve impulses. Atypical myocardium forms the conduction system of the heart. Physiological properties of atypical myocardium:

1) excitability is lower than that of skeletal muscles, but higher than that of contractile myocardial cells, therefore it is here that the generation of nerve impulses occurs;

2) conductivity is less than that of skeletal muscles, but higher than that of contractile myocardium;

3) the refractory period is quite long and is associated with the occurrence of an action potential and calcium ions;

4) low lability;

5) low ability to contractility;

6) automation (the ability of cells to independently generate a nerve impulse).

Atypical muscles form nodes and bundles in the heart, which are combined into conducting system. It includes:

1) sinoatrial node or Kis-Fleck (located on the posterior right wall, on the border between the superior and inferior vena cava);

2) atrioventricular node (lies in the lower part of the interatrial septum under the endocardium of the right atrium, it sends impulses to the ventricles);

3) bundle of His (goes through the atriogastric septum and continues in the ventricle in the form of two legs - right and left);

4) Purkinje fibers (they are branches of the legs of the bundle of His, which give their branches to cardiomyocytes).

There are also additional structures:

1) Kent's bundles (start from the atrial tracts and go along the lateral edge of the heart, connecting the atria and ventricles and bypassing the atrioventricular pathways);

2) Maygail's bundle (located below the atrioventricular node and transmits information to the ventricles, bypassing the bundles of His).

These additional tracts provide the transmission of impulses when the atrioventricular node is turned off, that is, they cause unnecessary information in pathology and can cause an extraordinary contraction of the heart - an extrasystole.

Thus, due to the presence of two types of tissues, the heart has two main physiological features - a long refractory period and automaticity.

4. Automatic heart

Automation - this is the ability of the heart to contract under the influence of impulses that arise in itself. It has been found that nerve impulses can be generated in atypical myocardial cells. In a healthy person, this occurs in the region of the sinoatrial node, since these cells differ from other structures in structure and properties. They are spindle-shaped, arranged in groups and surrounded by a common basement membrane. These cells are called first-order pacemakers, or pacemakers. They are metabolic processes at a high speed, so the metabolites do not have time to be carried out and accumulate in the intercellular fluid. Also characteristic properties are the low value of the membrane potential and high permeability for Na and Ca ions. A rather low activity of the sodium-potassium pump was noted, which is due to the difference in the concentration of Na and K.

Automaticity occurs in the diastole phase and is manifested by the movement of Na ions into the cell. In this case, the value of the membrane potential decreases and tends to a critical level of depolarization - slow spontaneous diastolic depolarization occurs, accompanied by a decrease in the membrane charge. During the phase of rapid depolarization, channels for Na and Ca ions open, and they begin their movement into the cell. As a result, the membrane charge decreases to zero and changes to the opposite, reaching +20-30 mV. The movement of Na occurs until electrochemical equilibrium is achieved in the Na ions, then the plateau phase begins. During the plateau phase, Ca ions continue to enter the cell. At this time, the heart tissue is inexcitable. Upon reaching electrochemical equilibrium in Ca ions, the plateau phase ends and a period of repolarization begins - the return of the membrane charge to the original level.

The action potential of the sinoatrial node has a smaller amplitude and is ± 70-90 mV, and the usual potential is equal to ± 120-130 mV.

Normally, potentials arise in the sinoatrial node due to the presence of cells - pacemakers of the first order. But other parts of the heart, under certain conditions, are also able to generate a nerve impulse. This occurs when the sinoatrial node is turned off and when additional stimulation is turned on.

When the sinoatrial node is switched off, the generation of nerve impulses with a frequency of 50-60 times per minute is observed in the atrioventricular node - the second-order pacemaker. If there is a disturbance in the atrioventricular node, with additional irritation, excitation occurs in the cells of the His bundle with a frequency of 30-40 times per minute - a third-order pacemaker.

automatic gradient - this is a decrease in the ability to automate as you move away from the sinoatrial node.

5. Energy supply of the myocardium

For the heart to work as a pump, a sufficient amount of energy is needed. The energy supply process consists of three stages:

1) education;

2) transport;

3) consumption.

Energy is generated in mitochondria in the form of adenosine triphosphate (ATP) during an aerobic reaction during the oxidation of fatty acids (mainly oleic and palmitic). During this process, 140 ATP molecules are formed. The energy supply can also occur due to the oxidation of glucose. But this is energetically less favorable, since the decomposition of 1 glucose molecule produces 30-35 ATP molecules. When the blood supply to the heart is disturbed, aerobic processes become impossible due to the lack of oxygen, and anaerobic reactions are activated. In this case, 1 ATP molecules come from 2 glucose molecule. This leads to heart failure.

The resulting energy is transported from mitochondria through myofibrils and has a number of features:

1) is carried out in the form of creatine phosphotransferase;

2) for its transport, the presence of two enzymes is necessary -

ATP-ADP-transferases and creatine phosphokinase

ATP by active transport with the participation of the enzyme ATP-ADP-transferase is transferred to the outer surface of the mitochondrial membrane and, using the active center of creatine phosphokinase and Mg ions, are delivered to creatine with the formation of ADP and creatine phosphate. ADP enters the active center of the translocase and is pumped into the mitochondria, where it undergoes rephosphorylation. Creatine phosphate is directed to muscle proteins with the current of the cytoplasm. It also contains the enzyme creatine phosphoxidase, which ensures the formation of ATP and creatine. Creatine with the current of the cytoplasm approaches the mitochondrial membrane and stimulates the process of ATP synthesis.

As a result, 70% of the generated energy is spent on muscle contraction and relaxation, 15% on the calcium pump, 10% on the sodium-potassium pump, and 5% on synthetic reactions.

6. Coronary blood flow, its features

For the full-fledged work of the myocardium, a sufficient supply of oxygen is necessary, which is provided by the coronary arteries. They begin at the base of the aortic arch. The right coronary artery supplies most of the right ventricle, the interventricular septum, the posterior wall of the left ventricle, and the remaining departments are supplied by the left coronary artery. The coronary arteries are located in the groove between the atrium and the ventricle and form numerous branches. The arteries are accompanied by coronary veins that drain into the venous sinus.

Features of coronary blood flow:

1) high intensity;

2) the ability to extract oxygen from the blood;

3) the presence of a large number of anastomoses;

4) high tone of smooth muscle cells during contraction;

5) a significant amount of blood pressure.

At rest, every 100 g of heart mass consumes 60 ml of blood. When transitioning to an active state, the intensity of coronary blood flow increases (in trained people it increases to 500 ml per 100 g, and in untrained people - up to 240 ml per 100 g).

At rest and activity, the myocardium extracts up to 70-75% of oxygen from the blood, and with an increase in oxygen demand, the ability to extract it does not increase. The need is met by increasing the intensity of blood flow.

Due to the presence of anastomoses, arteries and veins are connected to each other bypassing the capillaries. The number of additional vessels depends on two reasons: the fitness of the person and the ischemia factor (lack of blood supply).

Coronary blood flow is characterized by relatively high blood pressure. This is due to the fact that the coronary vessels start from the aorta. The significance of this lies in the fact that conditions are created for a better transition of oxygen and nutrients into the intercellular space.

During systole, up to 15% of blood enters the heart, and during diastole - up to 85%. This is due to the fact that during systole, contracting muscle fibers compress the coronary arteries. As a result, there is a portion ejection of blood from the heart, which is reflected in the magnitude of blood pressure.

Regulation of coronary blood flow is carried out using three mechanisms - local, nervous, humoral.

Autoregulation can be carried out in two ways - metabolic and myogenic. The metabolic method of regulation is associated with a change in the lumen of the coronary vessels due to substances formed as a result of metabolism. Expansion of coronary vessels occurs under the influence of several factors:

1) lack of oxygen leads to an increase in the intensity of blood flow;

2) an excess of carbon dioxide causes an accelerated outflow of metabolites;

3) adenosyl promotes the expansion of the coronary arteries and increased blood flow.

A weak vasoconstrictor effect occurs with an excess of pyruvate and lactate.

Myogenic effect of Ostroumov-Beilis is that smooth muscle cells begin to contract to stretch when blood pressure rises and relax when it falls. As a result, the blood flow velocity does not change with significant fluctuations in blood pressure.

Nervous regulation of coronary blood flow is carried out mainly by the sympathetic division of the autonomic nervous system and is activated with an increase in the intensity of coronary blood flow. This is due to the following mechanisms:

1) 2-adrenergic receptors predominate in the coronary vessels, which, when interacting with norepinephrine, lower the tone of smooth muscle cells, increasing the lumen of the vessels;

2) when the sympathetic nervous system is activated, the content of metabolites in the blood increases, which leads to the expansion of the coronary vessels, as a result, an improved blood supply to the heart with oxygen and nutrients is observed.

Humoral regulation is similar to the regulation of all types of vessels.

7. Reflex influences on the activity of the heart

The so-called cardiac reflexes are responsible for the two-way communication of the heart with the central nervous system. Currently, there are three reflex influences - own, conjugated, non-specific.

Own cardiac reflexes arise when the receptors located in the heart and blood vessels are excited, i.e., in the own receptors of the cardiovascular system. They lie in the form of clusters - reflexogenic or receptive fields of the cardiovascular system. In the area of reflexogenic zones there are mechano- and chemoreceptors. Mechanoreceptors will respond to changes in pressure in the vessels, to stretching, to changes in fluid volume. Chemoreceptors respond to changes in blood chemistry. Under normal conditions, these receptors are characterized by constant electrical activity. So, when the pressure or chemical composition of the blood changes, the impulse from these receptors changes. There are six types of intrinsic reflexes:

1) Bainbridge reflex;

2) influence from the area of carotid sinuses;

3) influence from the area of the aortic arch;

4) influence from the coronary vessels;

5) influence from pulmonary vessels;

6) influence from pericardial receptors.

Reflex influences from the area carotid sinuses - ampoule-shaped extensions of the internal carotid artery at the bifurcation of the common carotid artery. With an increase in pressure, impulses from these receptors increase, impulses are transmitted along the fibers of the IV pair of cranial nerves, and the activity of the IX pair of cranial nerves increases. As a result, irradiation of excitation occurs, and it is transmitted along the fibers of the vagus nerves to the heart, leading to a decrease in the strength and frequency of heart contractions.

With a decrease in pressure in the region of the carotid sinuses, impulses in the central nervous system decrease, the activity of the IV pair of cranial nerves decreases, and a decrease in the activity of the nuclei of the X pair of cranial nerves is observed. The predominant influence of the sympathetic nerves occurs, causing an increase in the strength and frequency of heart contractions.

The value of reflex influences from the area of the carotid sinuses is to ensure self-regulation of the activity of the heart.

With an increase in pressure, reflex influences from the aortic arch lead to an increase in impulses along the fibers of the vagus nerves, which leads to an increase in the activity of the nuclei and a decrease in the strength and frequency of heart contractions, and vice versa.

With an increase in pressure, reflex influences from the coronary vessels lead to inhibition of the heart. In this case, depression of pressure, depth of breathing and a change in the gas composition of the blood are observed.

When receptors from the pulmonary vessels are overloaded, inhibition of the work of the heart is observed.

When the pericardium is stretched or irritated by chemicals, inhibition of cardiac activity is observed.

Thus, their own cardiac reflexes self-regulate the amount of blood pressure and the work of the heart.

Conjugate cardiac reflexes include reflex influences from receptors that are not directly related to the activity of the heart. For example, these are receptors of internal organs, the eyeball, temperature and pain receptors of the skin, etc. Their significance lies in ensuring the adaptation of the work of the heart under changing conditions of the external and internal environment. They also prepare the cardiovascular system for the upcoming overload.

Nonspecific reflexes are normally absent, but they can be observed during the experiment.

Thus, reflex influences ensure the regulation of cardiac activity in accordance with the needs of the body.

8. Nervous regulation of the activity of the heart

Nervous regulation is characterized by a number of features.

1. The nervous system has a starting and corrective effect on the work of the heart, providing adaptation to the needs of the body.

2. The nervous system regulates the intensity of metabolic processes.

The heart is innervated by fibers of the central nervous system - extracardial mechanisms and by its own fibers - intracardial. The intracardiac regulatory mechanisms are based on the methsympathetic nervous system, which contains all the necessary intracardiac formations for the occurrence of a reflex arc and the implementation of local regulation. The fibers of the parasympathetic and sympathetic divisions of the autonomic nervous system, which provide afferent and efferent innervation, also play an important role. Efferent parasympathetic fibers are represented by the vagus nerves, the bodies of the first preganglionic neurons, located at the bottom of the rhomboid fossa of the medulla oblongata. Their processes end intramurally, and the bodies of II postganglionic neurons are located in the cardiac system. The vagus nerves provide innervation to the formations of the conduction system: the right one - the sinoatrial node, the left one - the atrioventricular node. The centers of the sympathetic nervous system lie in the lateral horns of the spinal cord at the level of the IV thoracic segments. It innervates the ventricular myocardium, atrial myocardium, and conduction system.

When the sympathetic nervous system is activated, the strength and frequency of heart contractions change.

The centers of the nuclei that innervate the heart are in a state of constant moderate excitation, due to which nerve impulses enter the heart. The tone of the sympathetic and parasympathetic divisions is not the same. In an adult, the tone of the vagus nerves predominates. It is supported by impulses coming from the central nervous system from receptors embedded in the vascular system. They lie in the form of nerve clusters of reflexogenic zones:

1) in the area of the carotid sinus;

2) in the region of the aortic arch;

3) in the area of coronary vessels.

When cutting the nerves coming from the carotid sinuses to the central nervous system, there is a decrease in the tone of the nuclei that innervate the heart.

The vagus and sympathetic nerves are antagonists and have five types of influence on the work of the heart:

1) chronotropic;

2) bathmotropic;

3) dromotropic;

4) inotropic;

5) tonotropic.

Parasympathetic nerves have a negative effect in all five directions, while sympathetic nerves have the opposite effect.

The afferent nerves of the heart transmit impulses from the central nervous system to the endings of the vagus nerves - primary sensory chemoreceptors that respond to changes in blood pressure. They are located in the myocardium of the atria and left ventricle. As pressure increases, the activity of the receptors increases, and excitation is transmitted to the medulla oblongata, the work of the heart reflexively changes. However, free nerve endings are found in the heart, which form subendocardial plexuses. They control the processes of tissue respiration. From these receptors, impulses travel to the neurons of the spinal cord and cause pain during ischemia.

Thus, the afferent innervation of the heart is performed mainly by the fibers of the vagus nerves, which connect the heart with the central nervous system.

9. Humoral regulation of the activity of the heart

Factors of humoral regulation are divided into two groups:

1) substances of systemic action;

2) substances of local action.

К systemic substances include electrolytes and hormones. Electrolytes (Ca ions) have a pronounced effect on the work of the heart (positive inotropic effect). With an excess of Ca, cardiac arrest can occur at the time of systole, since there is no complete relaxation. Na ions are able to have a moderate stimulating effect on the activity of the heart. With an increase in their concentration, a positive bathmotropic and dromotropic effect is observed. K ions in high concentrations have an inhibitory effect on the work of the heart due to hyperpolarization. However, a slight increase in K content stimulates coronary blood flow. It has now been found that with an increase in the level of K compared to Ca, a decrease in the work of the heart occurs, and vice versa.

The hormone adrenaline increases the strength and frequency of heart contractions, improves coronary blood flow and increases metabolic processes in the myocardium.

Thyroxine (thyroid hormone) enhances the work of the heart, stimulates metabolic processes, increases the sensitivity of the myocardium to adrenaline.

Mineralocorticoids (aldosterone) stimulate Na reabsorption and K excretion from the body.

Glucagon raises blood glucose levels by breaking down glycogen, resulting in a positive inotropic effect.

Sex hormones in relation to the activity of the heart are synergists and enhance the work of the heart.

Substances of local action act where they are produced. These include mediators. For example, acetylcholine has five types of negative effects on the activity of the heart, and norepinephrine has the opposite effect. Tissue hormones (kinins) are substances with high biological activity, but they are quickly destroyed, and therefore have a local effect. These include bradykinin, kalidin, moderately stimulating blood vessels. However, at high concentrations they can cause a decrease in heart function. Prostaglandins, depending on the type and concentration, can have different effects. Metabolites formed during metabolic processes improve blood flow.

Thus, humoral regulation ensures a longer adaptation of the activity of the heart to the needs of the body.

10. Vascular tone and its regulation

Vascular tone, depending on the origin, can be myogenic and nervous.

Myogenic tone occurs when some vascular smooth muscle cells begin to spontaneously generate a nerve impulse. The resulting excitation spreads to other cells, and contraction occurs. Tone is maintained by the basal mechanism. Different vessels have different basal tone: the maximum tone is observed in the coronary vessels, skeletal muscles, kidneys, and the minimum tone is observed in the skin and mucous membrane. Its significance lies in the fact that vessels with a high basal tone respond to strong irritation with relaxation, and those with a low tone respond with contraction.

The nervous mechanism occurs in vascular smooth muscle cells under the influence of impulses from the central nervous system. Due to this, there is an even greater increase in basal tone. This total tone is a resting tone, with an impulse frequency of 1-3 per second.

Thus, the vascular wall is in a state of moderate tension - vascular tone.

Currently, there are three mechanisms of regulation of vascular tone - local, nervous, humoral.

autoregulation provides a change in tone under the influence of local excitation. This mechanism is associated with relaxation and is manifested by the relaxation of smooth muscle cells. There is myogenic and metabolic autoregulation.

Myogenic regulation is associated with a change in the state of smooth muscles - this is the Ostroumov-Beilis effect, aimed at maintaining a constant level of blood volume supplied to the organ.

Metabolic regulation provides a change in the tone of smooth muscle cells under the influence of substances necessary for metabolic processes and metabolites. It is caused mainly by vasodilating factors:

1) lack of oxygen;

2) an increase in the content of carbon dioxide;

3) an excess of K, ATP, adenine, cATP.

Metabolic regulation is most pronounced in the coronary vessels, skeletal muscles, lungs, and brain. Thus, the mechanisms of autoregulation are so pronounced that in the vessels of some organs they offer maximum resistance to the constricting effect of the CNS.

Nervous regulation It is carried out under the influence of the autonomic nervous system, which acts as a vasoconstrictor and a vasodilator. Sympathetic nerves cause a vasoconstrictor effect in those in which β predominates₁-adrenergic receptors. These are the blood vessels of the skin, mucous membranes, gastrointestinal tract. Impulses along the vasoconstrictor nerves arrive both at rest (1-3 per second) and in the state of activity (10-15 per second).

Vasodilating nerves can be of various origins:

1) parasympathetic nature;

2) sympathetic nature;

3) axon reflex.

The parasympathetic division innervates the vessels of the tongue, salivary glands, pia mater, and external genitalia. The mediator acetylcholine interacts with the M-cholinergic receptors of the vascular wall, which leads to expansion.

The sympathetic department is characterized by innervation of the coronary vessels, vessels of the brain, lungs, and skeletal muscles. This is due to the fact that adrenergic nerve endings interact with β-adrenergic receptors, causing vasodilation.

The axon reflex occurs when skin receptors are irritated within the axon of one nerve cell, causing an expansion of the lumen of the vessel in this area.

Thus, the nervous regulation is carried out by the sympathetic department, which can have both expanding and constricting effects. The parasympathetic nervous system has a direct expanding effect.

Humoral regulation carried out by substances of local and systemic action.

Local substances include Ca ions, which have a narrowing effect and are involved in the occurrence of an action potential, calcium bridges, in the process of muscle contraction. K ions also cause vasodilation and in large quantities lead to hyperpolarization of the cell membrane. Na ions in excess can cause an increase in blood pressure and water retention in the body, changing the level of hormone secretion.

Hormones have the following effect:

1) vasopressin increases the tone of smooth muscle cells of arteries and arterioles, leading to their narrowing;

2) adrenaline is able to have an expanding and narrowing effect;

3) aldosterone retains Na in the body, affecting the vessels, increasing the sensitivity of the vascular wall to the action of angiotensin;

4) thyroxine stimulates metabolic processes in smooth muscle cells, which leads to narrowing;

5) renin is produced by cells of the juxtaglomerular apparatus and enters the bloodstream, acting on the angiotensinogen protein, which is converted to angiotensin II, leading to vasoconstriction;

6) atriopeptides have an expanding effect.

Metabolites (eg, carbon dioxide, pyruvic acid, lactic acid, H ions) act as chemoreceptors in the cardiovascular system, increasing the rate of impulse transmission in the CNS, resulting in reflex constriction.

Substances of local action produce a variety of effects:

1) mediators of the sympathetic nervous system have a mainly constricting effect, and the parasympathetic one has an expanding effect;

2) biologically active substances: histamine has an expanding effect, and serotonin has a contracting effect;

3) kinins (bradykinin and kalidin) cause an expanding effect;

4) prostaglandins mainly expand the lumen;

5) endothelial relaxation enzymes (a group of substances formed by endotheliocytes) have a pronounced local narrowing effect.

Thus, vascular tone is influenced by local, nervous and humoral mechanisms.

11. Functional system that maintains a constant level of blood pressure

Functional system that maintains a constant level of blood pressure, - a temporary set of organs and tissues, which is formed when the indicators deviate in order to return them to normal. The functional system consists of four links:

1) useful adaptive result;

2) central link;

3) executive level;

4) feedback.

Useful adaptive result - the normal value of blood pressure, with a change in which the impulse from the mechanoreceptors in the central nervous system increases, resulting in excitation.

Central link represented by the vasomotor center. When its neurons are excited, the impulses converge and converge on one group of neurons - the acceptor of the result of the action. In these cells, a standard for the final result arises, then a program is developed to achieve it.

Executive link includes internal organs:

1) heart;

2) vessels;

3) excretory organs;

4) organs of hematopoiesis and blood destruction;

5) depositing authorities;

6) the respiratory system (when the negative intrapleural pressure changes, the venous return of blood to the heart changes);

7) endocrine glands that secrete adrenaline, vasopressin, renin, aldosterone;

8) skeletal muscles that change motor activity.

As a result of the activity of the executive link, the blood pressure is restored. A secondary stream of impulses comes from the mechanoreceptors of the cardiovascular system, carrying information about changes in blood pressure to the central link. These impulses go to the neurons of the acceptor of the result of the action, where the result obtained is compared with the standard.

Thus, when the desired result is achieved, the functional system disintegrates.

At present, it is known that the central and executive mechanisms of a functional system are not switched on simultaneously, therefore by the time of inclusion allocate:

1) short-term mechanism;

2) intermediate mechanism;

3) long mechanism.

Short acting mechanisms turn on quickly, but the duration of their action is several minutes, a maximum of 1 hour. These include reflex changes in the work of the heart and the tone of blood vessels, that is, the nervous mechanism is the first to turn on.

intermediate mechanism begins to act gradually over several hours. This mechanism includes:

1) change in transcapillary exchange;

2) decrease in filtration pressure;

3) stimulation of the reabsorption process;

4) relaxation of tense vascular muscles after an increase in their tone.

Long acting mechanisms cause more significant changes in the functions of various organs and systems (for example, changes in kidney function due to changes in the volume of urine excreted). As a result, blood pressure is restored. The hormone aldosterone retains Na, which promotes water reabsorption and increases the sensitivity of smooth muscles to vasoconstrictor factors, primarily to the renin-angiotensin system.

Thus, when the blood pressure value deviates from the norm, various organs and tissues are combined in order to restore the indicators. In this case, three rows of barriers are formed:

1) decrease in vascular regulation and heart function;

2) decrease in the volume of circulating blood;

3) changes in the level of protein and formed elements.

12. Histohematic barrier and its physiological role

Histohematic barrier is the barrier between blood and tissue. They were first discovered by Soviet physiologists in 1929. The morphological substrate of the histohematic barrier is the capillary wall, which consists of:

1) fibrin film;

2) endothelium on the basement membrane;

3) a layer of pericytes;

4) adventitia.

In the body, they perform two functions - protective and regulatory.

Protective function associated with the protection of tissue from incoming substances (foreign cells, antibodies, endogenous substances, etc.).

Regulatory function is to ensure a constant composition and properties of the internal environment of the body, the conduction and transmission of molecules of humoral regulation, the removal of metabolic products from cells.

The histohematic barrier can be between tissue and blood and between blood and fluid.

The main factor affecting the permeability of the histohematic barrier is permeability. Permeability - the ability of the cell membrane of the vascular wall to pass various substances. It depends on:

1) morphofunctional features;

2) activities of enzyme systems;

3) mechanisms of nervous and humoral regulation.

Blood plasma contains enzymes that can change the permeability of the vascular wall. Normally, their activity is low, but with pathology or under the influence of factors, the activity of enzymes increases, which leads to increased permeability. These enzymes are hyaluronidase and plasmin. Nervous regulation is carried out according to the non-synaptic principle, since the transmitter enters the walls of the capillaries with the fluid flow. The sympathetic division of the autonomic nervous system reduces permeability, and the parasympathetic division increases it.

Humoral regulation is carried out by substances that are divided into two groups - increasing permeability and decreasing permeability.

The mediator acetylcholine, kinins, prostaglandins, histamine, serotonin, and metabolites that shift the pH to an acidic environment have an increasing effect.

Heparin, norepinephrine, Ca ions can have a lowering effect.

Histohematic barriers are the basis for the mechanisms of transcapillary exchange.

Thus, the structure of the vascular wall of capillaries, as well as physiological and physicochemical factors, greatly influence the work of histohematic barriers.

LECTURE No. 13. Physiology of respiration. Mechanisms of external respiration

1. Essence and significance of breathing processes

Breathing is the most ancient process through which the gas composition of the internal environment of the body is regenerated. As a result, organs and tissues are supplied with oxygen and give off carbon dioxide. Breathing is used in oxidative processes, during which energy is generated that is spent on growth, development and vital activity. The breathing process consists of three main parts - external respiration, gas transport by blood, and internal respiration.

External respiration represents the exchange of gases between the body and the external environment. It is carried out through two processes - pulmonary respiration and respiration through the skin.

Pulmonary respiration involves the exchange of gases between alveolar air and the environment and between alveolar air and capillaries. During gas exchange with the external environment, air enters containing 21% oxygen and 0,03-0,04% carbon dioxide, and exhaled air contains 16% oxygen and 4% carbon dioxide. Oxygen flows from atmospheric air into the alveolar air, and carbon dioxide is released in the opposite direction. When exchanged with the capillaries of the pulmonary circulation in the alveolar air, the oxygen pressure is 102 mmHg. Art., and carbon dioxide - 40 mm Hg. Art., venous blood oxygen tension - 40 mm Hg. Art., and carbon dioxide - 50 mm Hg. Art. As a result of external respiration, arterial blood, rich in oxygen and poor in carbon dioxide, flows from the lungs.

Gas transport by blood carried out mainly in the form of complexes:

1) oxygen forms a compound with hemoglobin, 1 g of hemoglobin binds 1,345 ml of gas;

2) 15-20 ml of oxygen is transported in the form of physical dissolution;

3) carbon dioxide is transported in the form of Na and K bicarbonates, with K bicarbonate located inside erythrocytes, and Na bicarbonate in the blood plasma;

4) carbon dioxide is transported along with the hemoglobin molecule.

internal breathing consists of the exchange of gases between the capillaries of the systemic circulation and tissue and interstitial respiration. As a result, oxygen is utilized for oxidative processes.

2. Apparatus for external respiration. The value of the components

In humans, external respiration is carried out with the help of a special apparatus, the main function of which is the exchange of gases between the body and the external environment.

The respiratory apparatus includes three components - the respiratory tract, lungs, chest, along with muscles.

Airways connect the lungs to the environment. They begin with the nasal passages, then continue into the larynx, trachea, and bronchi. Due to the presence of a cartilaginous base and periodic changes in the tone of smooth muscle cells, the lumen of the airways is always open. Its decrease occurs under the influence of the parasympathetic nervous system, and its expansion occurs under the influence of the sympathetic nervous system. The respiratory tract has a well-branched blood supply system, thanks to which the air is warmed and moistened. The epithelium of the airways is lined with cilia, which trap dust particles and microorganisms. The mucous membrane contains a large number of glands that produce secretions. Approximately 20-80 ml of secretion (mucus) is produced per day. The mucus contains lymphocytes and humoral factors (lysozyme, interferon, lactoferrin, proteases), immunoglobulins A, which provide a protective function. The respiratory tract contains a large number of receptors that form powerful reflexogenic zones. These are mechanoreceptors, chemoreceptors, taste receptors. Thus, the respiratory tract ensures constant interaction of the body with the environment and regulates the amount and composition of inhaled and exhaled air.

Lungs They are made up of alveoli with capillaries attached to them. The total area of their interaction is approximately 80-90 m². There is an air-blood barrier between the lung tissue and the capillary.

The lungs perform many functions:

1) remove carbon dioxide and water in the form of vapors (excretory function);

2) normalize the exchange of water in the body;

3) are blood depots of the second order;

4) take part in lipid metabolism in the process of surfactant formation;

5) participate in the formation of various blood coagulation factors;

6) provide inactivation of various substances;

7) take part in the synthesis of hormones and biologically active substances (serotonin, vasoactive intestinal polypeptide, etc.).

Rib cage together with the muscles forms a bag for the lungs. There is a group of inspiratory and expiratory muscles. The inspiratory muscles increase the size of the diaphragm, raise the anterior section of the ribs, expanding the anteroposterior and lateral openings, and lead to active deep inspiration. The expiratory muscles decrease the volume of the chest and lower the anterior ribs, causing exhalation.

Thus, breathing is an active process that is carried out only with the participation of all the elements involved in the process.

3. Inspiratory and expiratory mechanism

In an adult, the respiratory rate is approximately 16-18 breaths per minute. It depends on the intensity of metabolic processes and the gas composition of the blood.

The respiratory cycle consists of three phases:

1) inhalation phases (lasts approximately 0,9-4,7 s);

2) expiratory phases (lasting 1,2-6,0 s);

3) respiratory pause (non-constant component).

The type of breathing depends on the muscles, so they distinguish:

1) chest. It is carried out with the participation of the intercostal muscles and muscles of the 1-3rd respiratory gap, when inhaling, good ventilation of the upper section of the lungs is provided, typical for women and children under 10 years old;

2) abdominal. Inhalation occurs due to contractions of the diaphragm, leading to an increase in vertical size and, accordingly, better ventilation of the lower section, which is inherent in men;

3) mixed. It is observed with the uniform work of all respiratory muscles, accompanied by a proportional increase in the chest in three directions, observed in trained people.

In a calm state, breathing is an active process and consists of active inhalation and passive exhalation.

Active inhalation begins under the influence of impulses coming from the respiratory center to the inspiratory muscles, causing their contraction. This leads to an increase in the size of the chest and, accordingly, the lungs. Intrapleural pressure becomes more negative than atmospheric pressure and decreases by 1,5-3 mm Hg. Art. As a result of the pressure difference, air enters the lungs. At the end of the phase, the pressures equalize.

Passive exhalation occurs after the cessation of impulses to the muscles, they relax, and the size of the chest decreases.

If the flow of impulses from the respiratory center is directed to the expiratory muscles, then an active exhalation occurs. In this case, intrapulmonary pressure becomes equal to atmospheric.

With an increase in the respiratory rate, all phases are shortened.

Negative intrapleural pressure is the pressure difference between the parietal and visceral pleura. It is always below atmospheric. Factors that determine it:

1) uneven growth of the lungs and chest;

2) the presence of elastic recoil of the lungs.

The intensity of growth of the chest is higher than the tissue of the lungs. This leads to an increase in the volume of the pleural cavity, and since it is airtight, the pressure becomes negative.

Elastic recoil of the lungs - the force with which the fabric tends to fall. It occurs due to two reasons:

1) due to the presence of surface tension of the fluid in the alveoli;

2) due to the presence of elastic fibers.

Negative intrapleural pressure:

1) leads to the expansion of the lungs;

2) provides venous return of blood to the chest;

3) facilitates the movement of lymph through the vessels;

4) promotes pulmonary blood flow, as it keeps the vessels open.

The lung tissue, even with maximum expiration, does not completely collapse. This happens due to the presence surfactant, which lowers the tension of the fluid. Surfactant - a complex of phospholipids (mainly phosphatidylcholine and glycerol) is formed by type XNUMX alveolocytes under the influence of the vagus nerve.

Thus, a negative pressure is created in the pleural cavity, due to which the processes of inhalation and exhalation are carried out.

4. The concept of a breathing pattern

Pattern - a set of temporal and volumetric characteristics of the respiratory center, such as:

1) respiratory rate;

2) the duration of the respiratory cycle;

3) tidal volume;

4) minute volume;

5) maximum ventilation of the lungs, reserve volume of inhalation and exhalation;

6) vital capacity of the lungs.

The functioning of the external respiration apparatus can be judged by the volume of air entering the lungs during one respiratory cycle. The volume of air entering the lungs during maximum inhalation forms the total lung capacity. It is approximately 4,5-6 liters and consists of the vital capacity of the lungs and the residual volume.

Vital capacity of the lungs - the amount of air that a person can exhale after a deep breath. It is one of the indicators of the physical development of the body and is considered pathological if it is 70-80% of the proper volume. During life, this value may change. It depends on a number of reasons: age, height, body position in space, food intake, physical activity, the presence or absence of pregnancy.

The vital capacity of the lungs consists of respiratory and reserve volumes. Tidal volume - this is the amount of air that a person inhales and exhales in a calm state. Its size is 0,3-0,7 liters. It maintains the partial pressure of oxygen and carbon dioxide in the alveolar air at a certain level. Inspiratory reserve volume is the amount of air that a person can additionally inhale after a quiet breath. As a rule, this is 1,5-2,0 liters. It characterizes the ability of lung tissue to undergo additional stretching. Expiratory reserve volume is the amount of air that can be exhaled following a normal exhalation.

Residual volume is the constant volume of air remaining in the lungs even after maximum exhalation. It is about 1,0-1,5 liters.

An important characteristic of the respiratory cycle is the frequency of respiratory movements per minute. Normally, it is 16-20 movements per minute.

The duration of the respiratory cycle is calculated by dividing 60 s by the respiratory rate.

The entry and expiration times can be determined from the spirogram.

Minute volume - the amount of air exchanged with the environment during quiet breathing. It is determined by the product of the tidal volume and the respiratory rate and is 6-8 liters.

Maximum ventilation - the largest amount of air that can enter the lungs in 1 minute with increased breathing. On average, its value is 70-150 liters.

Respiratory cycle indicators are important characteristics that are widely used in medicine.

LECTURE No. 14. Physiology of the respiratory center

1. Physiological characteristics of the respiratory center

According to modern concepts respiratory center - this is a set of neurons that provide a change in the processes of inhalation and exhalation and adaptation of the system to the needs of the body. There are several levels of regulation:

1) spinal;

2) bulbar;

3) suprapontal;

4) cortical.

spinal level It is represented by motoneurons of the anterior horns of the spinal cord, the axons of which innervate the respiratory muscles. This component has no independent significance, as it obeys impulses from the overlying departments.

The neurons of the reticular formation of the medulla oblongata and the pons form bulbar level. The following types of nerve cells are distinguished in the medulla oblongata:

1) early inspiratory (excited 0,1-0,2 s before the start of active inspiration);

2) full inspiratory (activated gradually and send impulses throughout the inspiratory phase);

3) late inspiratory (they begin to transmit excitation as the action of the early ones fades);

4) post-inspiratory (excited after inhibition of inspiratory);

5) expiratory (provide the beginning of active exhalation);

6) preinspiratory (begin to generate a nerve impulse before inhalation).

The axons of these nerve cells can be directed to the motor neurons of the spinal cord (bulbar fibers) or be part of the dorsal and ventral nuclei (protobulbar fibers).

The neurons of the medulla oblongata, which are part of the respiratory center, have two features:

1) have a reciprocal relationship;

2) can spontaneously generate nerve impulses.

The pneumotoxic center is formed by the nerve cells of the bridge. They are able to regulate the activity of underlying neurons and lead to a change in the processes of inhalation and exhalation. If the integrity of the central nervous system in the region of the brainstem is violated, the respiratory rate decreases and the duration of the inspiratory phase increases.

Suprapontial level It is represented by the structures of the cerebellum and midbrain, which provide the regulation of motor activity and autonomic function.

Cortical component consists of neurons of the cerebral cortex, affecting the frequency and depth of breathing. Basically, they have a positive effect, especially on the motor and orbital zones. In addition, the participation of the cerebral cortex indicates the possibility of spontaneously changing the frequency and depth of breathing.

Thus, various structures of the cerebral cortex take on the regulation of the respiratory process, but the bulbar region plays a leading role.

2. Humoral regulation of respiratory center neurons

For the first time, humoral regulation mechanisms were described in the experiment of G. Frederick in 1860, and then studied by individual scientists, including I. P. Pavlov and I. M. Sechenov.

G. Frederick conducted a cross-circulation experiment in which he connected the carotid arteries and jugular veins of two dogs. As a result, the head of dog No. 1 received blood from the body of animal No. 2, and vice versa. When the trachea of dog No. 1 was compressed, carbon dioxide accumulated, which entered the body of animal No. 2 and caused an increase in the frequency and depth of breathing in him - hyperpnea. Such blood entered the head of dog No. 1 and caused a decrease in the activity of the respiratory center until respiratory arrest (hypopnea and apopnea). Experience proves that the gas composition of the blood directly affects the intensity of breathing.

The excitatory effect on the neurons of the respiratory center is exerted by:

1) decrease in oxygen concentration (hypoxemia);

2) an increase in the content of carbon dioxide (hypercapnia);

3) an increase in the level of hydrogen protons (acidosis).

Braking effect occurs as a result of:

1) increase in oxygen concentration (hyperoxemia);

2) lowering the content of carbon dioxide (hypocapnia);

3) decrease in the level of hydrogen protons (alkalosis).

Currently, scientists have identified five ways in which blood gas composition influences the activity of the respiratory center:

1) local;

2) humoral;

3) through peripheral chemoreceptors;

4) through central chemoreceptors;

5) through chemosensitive neurons of the cerebral cortex.

local action occurs as a result of the accumulation in the blood of metabolic products, mainly hydrogen protons. This leads to the activation of the work of neurons.

Humoral influence appears with an increase in the work of skeletal muscles and internal organs. As a result, carbon dioxide and hydrogen protons are released, which flow through the bloodstream to the neurons of the respiratory center and increase their activity.

Peripheral chemoreceptors - these are nerve endings from the reflexogenic zones of the cardiovascular system (carotid sinuses, aortic arch, etc.). They react to a lack of oxygen. In response, impulses are sent to the central nervous system, leading to an increase in the activity of nerve cells (Bainbridge reflex).

The reticular formation is composed of central chemoreceptors, which are highly sensitive to the accumulation of carbon dioxide and hydrogen protons. Excitation extends to all areas of the reticular formation, including the neurons of the respiratory center.

Nerve cells of the cerebral cortex also respond to changes in the gas composition of the blood.

Thus, the humoral link plays an important role in the regulation of the neurons of the respiratory center.

3. Nervous regulation of the activity of neurons of the respiratory center

Nervous regulation is carried out mainly by reflex pathways. There are two groups of influences - episodic and permanent.

There are three types of permanent:

1) from peripheral chemoreceptors of the cardiovascular system (Heimans reflex);

2) from the proprioreceptors of the respiratory muscles;

3) from nerve endings of lung tissue stretching.

During breathing, the muscles contract and relax. Impulses from proprioreceptors enter the CNS simultaneously to the motor centers and neurons of the respiratory center. Muscle work is regulated. If any obstruction of breathing occurs, the inspiratory muscles begin to contract even more. As a result, a relationship is established between the work of skeletal muscles and the body's need for oxygen.

Reflex influences from lung stretch receptors were first discovered in 1868 by E. Hering and I. Breuer. They found that nerve endings located in smooth muscle cells provide three types of reflexes:

1) inspiratory-braking;

2) expiratory-relieving;

3) Head's paradoxical effect.

During normal breathing, inspiratory-braking effects occur. During inhalation, the lungs expand, and impulses from receptors along the fibers of the vagus nerves enter the respiratory center. Here, inhibition of inspiratory neurons occurs, which leads to the cessation of active inhalation and the onset of passive exhalation. The significance of this process is to ensure the beginning of exhalation. When the vagus nerves are overloaded, the change of inhalation and exhalation is preserved.

The expiratory-relief reflex can only be detected during the experiment. If you stretch the lung tissue at the time of exhalation, then the onset of the next breath is delayed.

The paradoxical Head effect can be realized in the course of the experiment. With maximum stretching of the lungs at the time of inspiration, an additional breath or sigh is observed.

Episodic reflex influences include:

1) impulses from irritary receptors of the lungs;

2) influence from juxtaalveolar receptors;

3) influence from the mucous membrane of the respiratory tract;

4) influences from skin receptors.

Irritary receptors located in the endothelial and subendothelial layers of the respiratory tract. They simultaneously perform the functions of mechanoreceptors and chemoreceptors. Mechanoreceptors have a high threshold of irritation and are excited with a significant collapse of the lungs. Such falls normally occur 2-3 times per hour. With a decrease in the volume of lung tissue, receptors send impulses to the neurons of the respiratory center, which leads to an additional breath. Chemoreceptors respond to the appearance of dust particles in the mucus. When irritary receptors are activated, there is a feeling of sore throat and cough.

Juxtaalveolar receptors are located in the interstitium. They respond to the appearance of chemicals - serotonin, histamine, nicotine, as well as to changes in fluid. This leads to a special type of shortness of breath due to edema (pneumonia).

With severe irritation of the mucous membrane of the respiratory tract breathing stops, and in moderate cases protective reflexes appear. For example, when the receptors in the nasal cavity are irritated, sneezing occurs, and when the nerve endings of the lower respiratory tract are activated, a cough occurs.

The respiratory rate is influenced by impulses from temperature receptors. So, for example, when immersed in cold water, breath holding occurs.

Upon activation of noceceptors first there is a stoppage of breathing, and then there is a gradual increase.

During irritation of the nerve endings embedded in the tissues of the internal organs, there is a decrease in respiratory movements.

With an increase in pressure, a sharp decrease in the frequency and depth of breathing is observed, which leads to a decrease in the suction capacity of the chest and the restoration of blood pressure, and vice versa.

Thus, the reflex influences exerted on the respiratory center maintain the frequency and depth of breathing at a constant level.

LECTURE No. 15. Physiology of blood

1. Homeostasis. biological constants

The concept of the internal environment of the body was introduced in 1865 by Claude Bernard. It is a collection of body fluids that wash all organs and tissues and take part in metabolic processes, and includes blood plasma, lymph, interstitial, synovial and cerebrospinal fluid. Blood is called a universal fluid, since in order to maintain the normal functioning of the body it must contain all the necessary substances, i.e. the internal environment has constancy - homeostasis. But this constancy is relative, since the consumption of substances and the release of metabolites occurs all the time - homeostasis. In case of deviation from the norm, a functional system is formed that restores the changed indicators.

Homeostasis is characterized by certain average statistical indicators, which can fluctuate within small limits and have seasonal, gender and age differences.

Thus, according to the definition of P.K. Anokhin, all biological constants are divided into rigid and plastic. Rigid ones can fluctuate within small limits without significant disruption to life. These include blood pH, osmotic pressure, concentration of Na, R, Ca ions in blood plasma. Plastic can vary significantly without any consequences for the body.

This group includes the value of blood pressure, the level of glucose, fats, vitamins, etc.

Thus, biological constants form the state of the physiological norm.

Physiological norm - this is the optimal level of vital activity, at which the adaptation of the organism to the conditions of existence is ensured by changing the intensity of metabolic processes.

2. The concept of the blood system, its functions and significance. Physico-chemical properties of blood

The concept of the blood system was introduced in the 1830s. H. Lang. Blood is a physiological system that includes:

1) peripheral (circulating and deposited) blood;

2) hematopoietic organs;

3) organs of blood destruction;

4) mechanisms of regulation.

The blood system has a number of features:

1) dynamism, i.e. the composition of the peripheral component can constantly change;

2) the lack of independent significance, since it performs all its functions in constant motion, that is, it functions together with the circulatory system.

Its components are formed in various organs.

Blood performs many functions in the body:

1) transport;

2) respiratory;

3) nutritional;

4) excretory;

5) temperature control;

6) protective.

Blood also regulates the supply of nutrients to tissues and organs and maintains homeostasis.

The transport function consists of the transfer of most biologically active substances using plasma proteins (albumin and globulins). The respiratory function is carried out in the form of transport of oxygen and carbon dioxide. The nutritional function is that blood delivers nutrients - proteins, carbohydrates, lipids - to all organs and tissues. Due to the presence of high thermal conductivity, high heat transfer and the ability to easily and quickly move from deep organs to superficial tissues, blood regulates the level of heat exchange between the body and the environment. Metabolic products are delivered through the blood to the sites of excretion. The organs of hematopoiesis and blood destruction maintain various indicators at a constant level, i.e., they ensure homeostasis. The protective function is to participate in the reactions of nonspecific resistance of the body (innate immunity) and in acquired immunity, the fibrinolysis system due to the presence of leukocytes, platelets and erythrocytes.

Blood is a suspension, as it consists of formed elements suspended in plasma - leukocytes, platelets and erythrocytes. The ratio of plasma to formed elements depends on where the blood is located. Plasma predominates in the circulating blood - 50-60%, the content of formed elements - 40-45%. In deposited blood, on the contrary, plasma is 40-45%, and formed elements are 50-60%. To determine the percentage of plasma and formed elements, the hematocrit is calculated. Normally, it is 42 ± 5% in women, and 47 ± 7% in men.

Physico-chemical properties of blood are determined by its composition:

1) suspension;

2) colloidal;

3) rheological;

4) electrolyte.

Suspension property is associated with the ability of shaped elements to be in suspension. The colloidal property is provided mainly by proteins that can retain water (lyophilic proteins). The electrolyte property is associated with the presence of inorganic substances. Its indicator is the value of osmotic pressure. The rheological ability provides fluidity and influences the peripheral resistance.

LECTURE No. 16. Physiology of blood components

1. Blood plasma, its composition

Plasma is the liquid part of the blood and is a water-salt solution of proteins. Consists of 90-95% water and 8-10% solids. The composition of the dry residue includes inorganic and organic substances. Organic proteins include proteins, nitrogen-containing substances of non-protein nature, nitrogen-free organic components, enzymes.

Proteins make up 7-8% of the dry residue (which is 67-75 g/l) and perform a number of functions. They differ in structure, molecular weight, and content of various substances. When the protein concentration increases, hyperproteinemia occurs, when it decreases, hypoproteinemia occurs, when pathological proteins appear, paraproteinemia occurs, and when their ratio changes, dysproteinemia occurs. Normally, plasma contains albumin and globulins. Their ratio is determined by the protein coefficient, which is 1,5-2,0.

Albumins are finely dispersed proteins, the molecular weight of which is 70-000 D. They contain about 80-000% in plasma, which is 50-60 g / l. In the body, they perform the following functions:

1) are a depot of amino acids;

2) provide the suspension property of blood, since they are hydrophilic proteins and retain water;

3) are involved in maintaining colloidal properties due to the ability to retain water in the bloodstream;

4) transport hormones, non-esterified fatty acids, inorganic substances, etc.

With a lack of albumin, tissue edema occurs (up to the death of the body).

Globulins are coarse molecules with a molecular weight of more than 100 D. Their concentration ranges from 000-30%, which is about 35-30 g / l. During electrophoresis, globulins fall into several types:

1) β₁- globulins;

2) β₂-globulins;

3) β-globulins;

4) γ-globulins.

Due to this structure, globulins perform various functions:

1) protective;

2) transport;

3) pathological.

The protective function is associated with the presence of immunoglobulins - antibodies capable of binding antigens. They are also part of the body's defense systems, such as the properdin and complement systems, providing nonspecific resistance of the body. They participate in blood coagulation processes due to the presence of fibrinogen, which occupies an intermediate position between β-globulins and γ-globulins, which are the source of fibrin threads. They form a fibrinolysis system in the body, the main component of which is plasminogen.

The transport function is associated with the transfer of metals with the help of haptoglobin and ceruloplasmin. Haptoglobin belongs to β₂-globulins and forms a complex with transferrin, which preserves iron for the body. Ceruloplasmin is a β₂-globulin, which is able to combine copper.

Pathological globulins are formed during inflammatory reactions, therefore, they are not normally detected. These include interferon (formed by the introduction of viruses), C-reactive protein, or acute phase protein (is a β-globulin and is present in plasma in severe, chronic diseases).

Thus, proteins provide the physicochemical properties of blood and perform a protective function.

Plasma also contains amino acids, urea, uric acid, creatinine;

Their content is low, so they are referred to as residual blood nitrogen. Normally, it is approximately 14,3-28,6%. The level of residual nitrogen is maintained due to the presence of proteins in food, the excretory function of the kidneys and the intensity of protein metabolism.

Organic substances in plasma are presented in the form of metabolic products of carbohydrates and lipids. Components of carbohydrate metabolism:

1) glucose, the content of which is normally 4,44-6,66 mmol / l in arterial blood and 3,33-5,55 mmol / l in venous blood and depends on the amount of carbohydrates in food, the state of the endocrine system;

2) lactic acid, the content of which rises sharply in critical conditions. Normally, its content is 1-1,1 mmol / l;

3) pyruvic acid (formed during the utilization of carbohydrates, normally contains approximately 80-85 mmol/l). The product of lipid metabolism is cholesterol, which is involved in the synthesis of hormones, bile acids, the construction of cell membranes, and performs an energy function. In free form, it is presented in the form of lipoproteins - a complex of proteins and lipids. There are five groups:

1) chylomicrons (participate in the transport of triacylglycerides of exogenous origin, are formed in the endoplasmic reticulum of enterocytes);

2) very low density lipoproteins (carry triacylglycerides of endogenous origin);

3) low density lipoproteins (deliver cholesterol to cells and tissues);

4) high density lipoproteins (form complexes with cholesterol and phospholipids).

Biologically active substances and enzymes belong to the group of substances with high enzymatic activity, they account for 0,1% of the dry residue.

Inorganic substances are electrolytes, i.e. anions and cations. They perform a number of functions:

1) regulate osmotic pressure;

2) maintain blood pH;

3) participate in the excitation of the cell membrane.

Each element has its own functions:

1) iodine is necessary for the synthesis of thyroid hormones;

2) iron is part of hemoglobin;

3) copper catalyzes erythropoiesis.

The osmotic pressure of the blood is provided by the concentration of osmotically active substances in the blood, i.e., this is the pressure difference between electrolytes and non-electrolytes.

Osmotic pressure is a rigid constant, its value is 7,3-8,1 atm. Electrolytes create up to 90-96% of the total osmotic pressure, of which 60% is sodium chloride, since electrolytes have a low molecular weight and create a high molecular concentration. Non-electrolytes make up 4-10% of the osmotic pressure and have a high molecular weight, therefore creating a low osmotic concentration. These include glucose, lipids, and blood plasma proteins. The osmotic pressure created by proteins is called oncotic. With its help, the formed elements are maintained in suspension in the bloodstream. To maintain normal life functions, it is necessary that the osmotic pressure always be within the acceptable range.

2. Physiology of erythrocytes

Erythrocytes are red blood cells containing the respiratory pigment - hemoglobin. These anucleate cells are formed in the red bone marrow and destroyed in the spleen. Depending on their size, they are divided into normocytes, microcytes and macrocytes. Approximately 85% of all cells have the shape of a biconcave disk or lens with a diameter of 7,2-7,5 microns. This structure is due to the presence of the spectrin protein in the cytoskeleton and the optimal ratio of cholesterol and lecithin. Thanks to this form, the red blood cell is able to transport respiratory gases - oxygen and carbon dioxide.

The most important functions of the erythrocyte are:

1) respiratory;

2) nutritious;

3) enzymatic;

4) protective;

5) buffer.

Hemoglobin is involved in immunological reactions.

Respiratory function is associated with the presence of hemoglobin and potassium bicarbonate, due to which the transport of respiratory gases is carried out.

The nutritional function is associated with the ability of the cell membrane to adsorb amino acids and lipids, which are transported from the intestines to the tissues with the blood flow.

The enzymatic function is due to the presence on the membrane of carbonic anhydrase, methemoglobin reductase, glutathione reductase, peroxidase, true cholinesterase, etc.

The protective function is carried out as a result of the deposition of microbial toxins and antibodies, as well as due to the presence of blood coagulation factors and fibrinolysis.

Since red blood cells contain antigens, they are used in immunological reactions to detect antibodies in the blood.

Erythrocytes are the most numerous formed elements of blood. So, men normally contain 4,5-5,5 × 10¹²/l, and for women - 3,7-4,7 × 10¹²/l. However, the number of blood cells is variable (an increase is called erythrocytosis, and a decrease is called erythropenia).

Erythrocytes have physiological and physico-chemical properties:

1) plasticity;

2) osmotic resistance;

3) the presence of creative connections;

4) the ability to settle;

5) aggregation;

6) destruction.

Plasticity is largely due to the structure of the cytoskeleton, in which the ratio of phospholipids and cholesterol is very important. This ratio is expressed as a lipolytic coefficient and is normally 0,9. Erythrocyte plasticity - the ability to reversible deformation when passing through narrow capillaries and micropores. With a decrease in the amount of cholesterol in the membrane, a decrease in the resistance of erythrocytes is observed.

The osmotic pressure in cells is slightly higher than in plasma due to the intracellular concentration of proteins. The mineral composition also affects the osmotic pressure (potassium predominates in erythrocytes and the content of Na ions is reduced). Due to the presence of osmotic pressure, normal turgor is ensured.

It has now been established that erythrocytes are ideal carriers, since they have creative bonds, transport various substances and carry out intercellular interaction.

The ability to settle is due to the specific gravity of the cells, which is higher than all blood plasma. Normally, it is low and is associated with the presence of proteins of the albumin fraction, which are able to retain the hydration membrane of erythrocytes. Globulins are lyophobic colloids that prevent the formation of a hydration shell. The ratio of albumin and globulin blood fractions (protein coefficient) determines the erythrocyte sedimentation rate. Normally, it is 1,5-1,7.

With a decrease in blood flow velocity and an increase in viscosity, aggregation is observed. With rapid aggregation, “coin columns” are formed - false aggregates that disintegrate into full-fledged cells with a preserved membrane and intracellular structure. With prolonged disruption of blood flow, true aggregates appear, causing the formation of a microthrombus.

Destruction (destruction of red blood cells) occurs after 120 days as a result of physiological aging. It is characterized by:

1) a gradual decrease in the content of lipids and water in the membrane;

2) increased output of K and Na ions;

3) the predominance of metabolic shifts;

4) deterioration in the ability to restore methemoglobin to hemoglobin;

5) a decrease in osmotic resistance, leading to hemolysis.

Aging erythrocytes, due to a decrease in the ability to deform, get stuck in the millipore filters of the spleen, where they are absorbed by phagocytes. About 10% of cells are destroyed in the vascular bed.

3. Types of hemoglobin and its significance

Hemoglobin is one of the most important respiratory proteins involved in the transfer of oxygen from the lungs to the tissues. It is the main component of red blood cells, each of which contains approximately 280 million hemoglobin molecules.

Hemoglobin is a complex protein that belongs to the class of chromoproteins and consists of two components:

1) iron-containing heme - 4%;

2) globin protein - 96%.

Heme is a complex compound of porphyrin with iron. This compound is rather unstable and easily converts to either hematin or hemin. The heme structure is identical for hemoglobin in all animal species. The differences are associated with the properties of the protein component, which is represented by two pairs of polypeptide chains. There are HbA, HbF, HbP forms of hemoglobin.

The blood of an adult contains up to 95-98% of hemoglobin HbA. Its molecule includes 2 α- and 2 β-polypeptide chains. Fetal hemoglobin is normally found only in newborns. In addition to normal types of hemoglobin, there are also abnormal ones that are produced under the influence of gene mutations at the level of structural and regulatory genes.

Inside the red blood cell, hemoglobin molecules are distributed in different ways. Near the membrane they lie perpendicular to it, which improves the interaction of hemoglobin with oxygen. In the center of the cell they lie more chaotically. In men, the normal hemoglobin content is approximately 130-160 g/l, and in women - 120-140 g/l.

There are four forms of hemoglobin:

1) oxyhemoglobin;

2) methemoglobin;

3) carboxyhemoglobin;

4) myoglobin.

Oxyhemoglobin contains ferrous iron and is able to bind oxygen. It carries gas to tissues and organs. When exposed to oxidizing agents (peroxides, nitrites, etc.), iron changes from a divalent to a trivalent state, due to which methemoglobin is formed, which does not reversibly react with oxygen and ensures its transport. Carboxyhemoglobin forms a compound with carbon monoxide. It has a high affinity for carbon monoxide, so the complex decomposes slowly. This causes the high toxicity of carbon monoxide. Myoglobin is similar in structure to hemoglobin and is found in muscles, especially in the heart. It binds oxygen, forming a depot, which is used by the body when the oxygen capacity of the blood decreases. Due to myoglobin, oxygen is provided to working muscles.

Hemoglobin performs respiratory and buffering functions. 1 mole of hemoglobin is capable of binding 4 moles of oxygen, and 1 g - 1,345 ml of gas. Blood oxygen capacity - the maximum amount of oxygen that can be in 100 ml of blood. When performing the respiratory function, the hemoglobin molecule changes in size. The ratio between hemoglobin and oxyhemoglobin depends on the degree of partial pressure in the blood. The buffering function is associated with the regulation of blood pH.

4. Physiology of leukocytes

leukocytes - nucleated blood cells, the size of which is from 4 to 20 microns. Their life expectancy varies greatly and ranges from 4-5 to 20 days for granulocytes and up to 100 days for lymphocytes. The number of leukocytes is normal in men and women is the same and is 4-9 × 10⁹/ l. However, the level of cells in the blood is not constant and is subject to daily and seasonal fluctuations in accordance with changes in the intensity of metabolic processes.

Leukocytes are divided into two groups: granulocytes (granular) and agranulocytes.

Among granulocytes in peripheral blood are found:

1) neutrophils - 46-76%;

2) eosinophils - 1-5%;

3) basophils - 0-1%.

In the group of nongranular cells, there are:

1) monocytes - 2-10%;

2) lymphocytes - 18-40%.

The percentage of leukocytes in peripheral blood is called the leukocyte formula, shifts of which in different directions indicate pathological processes occurring in the body. There is a shift to the right - a decrease in the function of red bone marrow, accompanied by an increase in the number of old forms of neutrophilic leukocytes. The shift to the left is a consequence of increased functions of the red bone marrow; the number of young forms of leukocytes in the blood increases. Normally, the ratio between young and old forms of leukocytes is 0,065 and is called the regeneration index. Due to the presence of a number of physiological characteristics leukocytes are able to perform many functions. The most important of the properties are amoeboid mobility, migration (the ability to penetrate through the wall of intact vessels), phagocytosis.

Leukocytes perform protective, destructive, regenerative, enzymatic functions in the body.

The protective property is associated with the bactericidal and antitoxic action of agranulocytes, participation in the processes of blood coagulation and fibrinolysis.

Destructive action consists in phagocytosis of dying cells.

Regenerative activity promotes wound healing.

The enzymatic role is associated with the presence of a number of enzymes.

Immunity - the body’s ability to protect itself from genetically foreign substances and bodies. Depending on the origin, it can be hereditary or acquired. It is based on the production of antibodies to the action of antigens. There are cellular and humoral components of immunity. Cellular immunity is provided by the activity of T-lymphocytes, and humoral immunity by B-lymphocytes.

5. Physiology of platelets

Platelets - non-nuclear blood cells, 1,5-3,5 microns in diameter. They have a flattened shape, and their number in men and women is the same and is 180-320 × 10⁹/ l. These cells are formed in the red bone marrow by lacing off megakaryocytes.

The platelet contains two zones: the granule (the center where glycogen, blood coagulation factors, etc. are located) and the hyalomere (the peripheral part, consisting of the endoplasmic reticulum and Ca ions).

The membrane is built from a bilayer and is rich in receptors. Receptors according to their function are divided into specific and integrated. Specific ones are able to interact with various substances, due to which mechanisms are launched that are similar to the action of hormones. Integrated provide interaction between platelets and endotheliocytes.

Platelets are characterized by the following properties:

1) amoeboid mobility;

2) fast destructibility;

3) the ability to phagocytosis;

4) the ability to adhere;

5) the ability to aggregate.

Platelets perform trophic and dynamic functions and regulate vascular tone and take part in blood coagulation processes.

The trophic function is to provide the vascular wall with nutrients, due to which the vessels become more elastic.

Regulation of vascular tone is achieved due to the presence of a biological substance - serotonin, which causes contractions of smooth muscle cells. Tramboxan A2 (arachidonic acid derivative) ensures the onset of a vasoconstrictor effect by reducing vascular tone.

The platelet takes an active part in the processes of blood coagulation due to the content of platelet factors in the granules, which are formed either in platelets or adsorbed in the blood plasma.

The dynamic function consists in the processes of adhesion and aggregation of blood clots. Adhesion - the process is passive, proceeding without energy expenditure. The thrombus begins to adhere to the surface of the vessels due to intergin receptors for collagen and, when damaged, is released to the surface to fibronectin. Aggregation occurs in parallel with adhesion and proceeds with the expenditure of energy. Therefore, the main factor is the presence of ADP. When ADP interacts with receptors, activation of the J-protein on the inner membrane begins, which causes the activation of phospholipases A and C. Phospholipase a promotes the formation of thromboxane A2 (aggregant) from arachidonic acid. Phospholipase c promotes the formation of inazitol triphosphate and diacylglycerol. As a result, protein kinase C is activated, and the permeability for Ca ions increases. As a result, they enter the cytoplasm from the endoplasmic reticulum, where Ca activates calmodulin, which activates calcium-dependent protein kinase.

LECTURE No. 17. Physiology of blood. blood immunology

1. Immunological basis for determining the blood group

Karl Landsteiner discovered that the red blood cells of some people are glued together by the blood plasma of other people. The scientist established the existence of special antigens - agglutinogens - in erythrocytes and assumed the presence of corresponding antibodies - agglutinins - in the blood serum. He described three blood groups according to the ABO system. Blood group IV was discovered by Jan Janski. The blood group is determined by isoantigens; in humans there are about 0 of them. They are combined into group antigen systems, their carriers are erythrocytes. Isoantigens are inherited, constant throughout life, and do not change under the influence of exo- and endogenous factors.

Antigens - high-molecular polymers of natural or artificial origin, which carry signs of genetically alien information. The body reacts to antigens by producing specific antibodies.

Antibodies Immunoglobulins are formed when an antigen is introduced into the body. They are able to interact with antigens of the same name and cause a number of reactions. There are normal (complete) and incomplete antibodies. Normal antibodies (α- and β-agglutinins) are found in the serum of people not immunized with antigens. Incomplete antibodies (anti-Rhesus agglutinins) are formed in response to the introduction of an antigen. There are four blood groups in the AB0 antigenic system. Antigens (agglutinogens A, B) are polysaccharides, they are located in the erythrocyte membrane and are associated with proteins and lipids. The erythrocytes may contain antigen 0, it has mild antigenic properties, therefore there are no agglutinins of the same name in the blood.

Antibodies (agglutinins α and β) are found in the blood plasma. Agglutinogens and agglutinins of the same name are not found in the blood of the same person, since in this case an agglutination reaction would occur.

It is accompanied by agglutination and destruction (hemolysis) of red blood cells.

The division into blood groups of the AB0 system is based on combinations of erythrocyte agglutinogens and plasma agglutinins.

I (0) - there are no agglutinogens in the erythrocyte membrane, α- and β-agglutinins are present in the blood plasma.

II (A) - agglutinogen is present in the erythrocyte membrane.

A, in blood plasma - α-agglutinin.

III (B) - agglutinogen is present in the erythrocyte membrane.

B, in blood plasma - β-agglutinin.

IV (AB) - agglutinogen A and agglutinogen B are present in the erythrocyte membrane, there are no agglutinins in the plasma.

To determine the blood type, standard hemagglutinating sera of I, II, III, IV groups of two series with different antibody titers are used.

When mixing blood with sera, an agglutination reaction occurs or it is absent. The presence of agglutination of erythrocytes indicates the presence in erythrocytes of an agglutinogen of the same name as agglutinin in this serum. The absence of agglutination of erythrocytes indicates the absence of agglutinogen in erythrocytes, which is the same name as the agglutinin of this serum.

Careful determination of blood groups of the donor and recipient according to the AB0 antigenic system is necessary for successful blood transfusion.

2. Antigenic system of erythrocytes, immune conflict

Antigens are high-molecular polymers of natural or artificial origin that carry signs of genetically alien information.

Antibodies are immunoglobulins that are formed when an antigen is introduced into the body.

Isoantigens (intraspecific antigens) are antigens that originate from one species of organisms, but are genetically alien to each individual. The most important are erythrocyte antigens, especially antigens of the AB0 system and the Rh-hr system.

An immunological conflict in the AB0 system occurs when antigens and antibodies of the same name meet, causing erythrocyte agglutination and their hemolysis. Immunological conflict is observed:

1) when transfusing a blood group that is incompatible in a group relation;

2) when transfusing large amounts of blood groups to people with other blood groups.

When transfusing blood, take into account the direct and reverse Ottenberg's rule.

Ottenberg's direct rule: when transfusing small volumes of blood (1/10 of the circulating blood volume), pay attention to the donor's red blood cells and the recipient's plasma - a person with blood group I is a universal donor.

Ottenberg's reverse rule: when transfusing large volumes of blood (more than 1/10 of the circulating blood volume), pay attention to the donor's plasma and the recipient's red blood cells. A person with blood group IV is a universal recipient.

Currently, it is recommended to transfuse only single-group blood and only in small quantities.

Rh antigenic system discovered in 1940 by K. Landsteiner and A. Wiener.

They found in the blood serum of macaque monkeys, Rh antibodies - anti-Rhesus agglutinin.

Rhesus system antigens - lipoproteins. Erythrocytes of 85% of people contain Rh-agglutinogen, their blood is Rh-positive, 15% of people do not have Rh antigen, their blood is Rh-negative. Six varieties of antigens of the Rh system have been described. The most important are Rh0 (D), rh`(C), rh "(E). The presence of at least one of the three antigens indicates that the blood is Rh-positive.

The peculiarity of the Rh system is that it does not have natural antibodies, they are immune and are formed after sensitization - contact of Rh- blood with Rh+.

During the primary transfusion of Rh- to a person, Rh + blood does not develop Rh conflict, since there are no natural anti-Rh agglutinins in the recipient's blood.

An immunological conflict in the Rh antigenic system occurs during repeated transfusion of Rh (-) blood to a person with Rh +, in cases of pregnancy, when the woman is Rh (-), and the fetus is Rh +.

During the first pregnancy of an Rh (-) mother, an Rh + fetus does not develop a Rh conflict, since the antibody titer is low. Immune anti-Rhesus agglutinins do not cross the placental barrier. They have a large protein molecule (class M immunoglobulin).

With repeated pregnancy, the antibody titer increases. Anti-Rh agglutinins (class G immunoglobulins) have a small molecular weight and easily penetrate the placental barrier into the fetus, where they cause agglutination and hemolysis of red blood cells.

LECTURE No. 18. Physiology of hemostasis

1. Structural components of hemostasis

Hemostasis - a complex biological system of adaptive reactions, which ensures the preservation of the liquid state of blood in the vascular bed and stop bleeding from damaged vessels by thrombosis. The hemostasis system includes the following components:

1) vascular wall (endothelium);

2) blood cells (platelets, leukocytes, erythrocytes);

3) plasma enzyme systems (blood coagulation system, fibrinolysis system, clecrein-kinin system);

4) mechanisms of regulation.

Functions of the hemostasis system.

1. Maintaining blood in the vascular bed in a liquid state.

2. Stop bleeding.

3. Mediation of interprotein and intercellular interactions.

4. Opsonic - cleaning the bloodstream from products of phagocytosis of a non-bacterial nature.

5. Reparative - healing of injuries and restoration of the integrity and viability of blood vessels and tissues.

Factors that maintain the liquid state of the blood:

1) thromboresistance of the endothelium of the vessel wall;

2) inactive state of plasma coagulation factors;

3) the presence of natural anticoagulants in the blood;

4) the presence of a fibrinolysis system;

5) continuous circulating blood flow.

Thromboresistance of the vascular endothelium is provided by antiplatelet, anticoagulant and fibrinolytic properties.

Antiplatelet properties:

1) synthesis of prostacyclin, which has antiaggregatory and vasodilating effects;

2) synthesis of nitric oxide, which has antiaggregatory and vasodilating effects;

3) the synthesis of endothelins, which constrict blood vessels and prevent platelet aggregation.

Anticoagulant properties:

1) synthesis of the natural anticoagulant antithrombin III, which inactivates thrombin. Antithrombin III interacts with heparin, forming an anticoagulant potential at the border of the blood and the vessel wall;

2) the synthesis of thrombomodulin, which binds the active thrombin enzyme and disrupts the formation of fibrin by activating the natural anticoagulant protein C.

Fibrinolytic properties are provided by the synthesis of tissue plasminogen activator, which is a powerful activator of the fibrinolysis system. There are two mechanisms of hemostasis:

1) vascular-platelet (microcircular);

2) coagulation (blood clotting).

A full-fledged hemostatic function of the body is possible under the condition of close interaction of these two mechanisms.

2. Mechanisms of platelet and coagulation thrombus formation

The vascular-platelet mechanism of hemostasis ensures that bleeding stops in the smallest vessels, where there is low blood pressure and a small lumen of the vessels. Stop bleeding can occur due to:

1) vascular contractions;

2) platelet plug formation;

3) combinations of both.

The vascular-platelet mechanism ensures stopping bleeding due to the ability of the endothelium to synthesize and release into the blood biologically active substances that change the lumen of blood vessels, as well as the adhesive-aggregation function of platelets. Changes in the lumen of blood vessels occur due to contraction of the smooth muscle elements of the vascular walls, both reflexively and humorally. Platelets have the ability of adhesion (the ability to stick to a foreign surface) and aggregation (the ability to stick together). This promotes the formation of a platelet plug and starts the blood clotting process. Stopping bleeding due to the vascular-platelet mechanism of hemostasis is carried out as follows: in case of injury, vascular spasm occurs due to reflex contraction (short-term primary spasm) and the action of biologically active substances on the vascular wall (serotonin, adrenaline, norepinephrine), which are released from platelets and damaged tissue . This spasm is secondary and longer lasting. In parallel, a platelet plug is formed, which closes the lumen of the damaged vessel. Its formation is based on the ability of platelets to adhesion and aggregation. Platelets are easily destroyed and release biologically active substances and platelet factors. They promote vasospasm and trigger the blood clotting process, which results in the formation of the insoluble protein fibrin. Fibrin threads entwine platelets, and a fibrin-platelet structure is formed - a platelet plug. A special protein is released from platelets - thrombostein, under the influence of which there is a contraction of the platelet plug and the formation of a platelet thrombus. The thrombus firmly closes the lumen of the vessel, and the bleeding stops.

The coagulation mechanism of hemostasis ensures stopping bleeding in larger vessels (muscle-type vessels). Bleeding is stopped by blood clotting - hemocoagulation. The process of blood clotting involves the transition of the soluble blood plasma protein fibrinogen into the insoluble protein fibrin. The blood changes from a liquid state to a gelatinous state, a clot is formed that closes the lumen of the vessel. The clot consists of fibrin and precipitated blood elements - red blood cells. A clot attached to the wall of a vessel is called a thrombus; it undergoes further retraction (contraction) and fibrinolysis (dissolution). Blood clotting factors take part in blood clotting. They are found in blood plasma, formed elements, and tissues.

3. Blood clotting factors

Many factors take part in the process of blood coagulation, they are called blood coagulation factors, they are contained in blood plasma, formed elements and tissues. Plasma coagulation factors are of the greatest importance.

Plasma coagulation factors are proteins, most of which are enzymes. They are in an inactive state, synthesized in the liver and activated during blood clotting. Exists fifteen plasma coagulation factors, the main ones are the following.

I - fibrinogen - a protein that passes into fibrin under the influence of thrombin, is involved in platelet aggregation, is necessary for tissue repair.

II - prothrombin - a glycoprotein that passes into thrombin under the influence of prothrombinase.

IV - Ca ions are involved in the formation of complexes, is part of prothrombinase, binds heparin, promotes platelet aggregation, takes part in the retraction of the clot and platelet plug, and inhibits fibrinolysis.

Additional factors that accelerate the process of blood clotting, are accelerators (factors V to XIII).

VII - proconvertin - a glycoprotein involved in the formation of prothrombinase by an external mechanism;

X - Stuart-Prauer factor - a glycoprotein that is an integral part of prothrombinase.

XII - Hageman factor - a protein that is activated by negatively charged surfaces, adrenaline. It triggers the external and internal mechanism for the formation of prothrombinase, as well as the mechanism of fibrinolysis.

Cell surface factors:

1) tissue activator that induces blood coagulation;

2) a procoagulant phospholipid that acts as a lipid component of tissue factor;

3) thrombomodulin, which binds thrombin on the surface of endothelial cells, activates protein C.

Blood coagulation factors of formed elements.

Erythrocyte:

1) phospholipid factor;

2) a large amount of ADP;

3) fibrinase.

Leukocytes - apoprotein III, significantly accelerating blood clotting, contributing to the development of widespread intravascular coagulation.

The tissue factor is thromboplastin, which is contained in the cerebral cortex, in the lungs, in the placenta, vascular endothelium, contributes to the development of widespread intravascular coagulation.

4. Phases of blood coagulation

blood clotting - This is a complex enzymatic, chain (cascade), matrix process, the essence of which is the transition of the soluble fibrinogen protein to the insoluble fibrin protein. The process is called cascade, since during the course of coagulation there is a sequential chain activation of blood coagulation factors. The process is matrix, since the activation of hemocoagulation factors occurs on the matrix. The matrix is the phospholipids of the membranes of destroyed platelets and fragments of tissue cells.

The process of blood clotting occurs in three phases.

The essence of the first phase is the activation of the X-factor of blood coagulation and the formation of prothrombinase. prothrombinase is a complex complex consisting of active X-factor of blood plasma, active V-factor of blood plasma and the third platelet factor. The activation of the X factor occurs in two ways. The division is based on the source of the matrices on which the cascade of enzymatic processes takes place. At external mechanism of activation, the source of matrices is tissue thromboplastin (phospholipid fragments of cell membranes of damaged tissues), with domestic - exposed collagen fibers, phospholipid fragments of cell membranes of blood cells.

The essence of the second phase is the formation of the active proteolytic enzyme thrombin from an inactive precursor of prothrombin under the influence of prothrombinase. This phase requires Ca ions.

The essence of the third phase is the transition of the soluble plasma protein fibrinogen into insoluble fibrin. This phase is carried out three 3 stages.

1. Proteolytic. Thrombin has esterase activity and cleaves fibrinogen to form fibrin monomers. The catalyst for this stage are Ca ions, II and IX prothrombin factors.

2. Physico-chemical, or polymerization stage. It is based on a spontaneous self-assembly process leading to the aggregation of fibrin monomers, which proceeds according to the "side-to-side" or "end-to-end" principle. Self-assembly is carried out by forming longitudinal and transverse bonds between fibrin monomers with the formation of a fibrin polymer (fibrin-S). Fibrin-S fibers are easily lysed not only under the influence of plasmin, but also complex compounds that do not have fibrinolytic activity.

3. Enzymatic. Fibrin is stabilized in the presence of active plasma factor XIII. Fibrin-S turns into fibrin-I (insoluble fibrin). Fibrin-I attaches to the vascular wall, forms a network where blood cells (red blood cells) become entangled and a red blood clot is formed, which closes the lumen of the damaged vessel. Subsequently, retraction of the blood clot is observed - the fibrin threads contract, the clot becomes denser, decreases in size, and serum rich in the enzyme thrombin is squeezed out of it. Under the influence of thrombin, fibrinogen turns back into fibrin, due to which the clot increases in size, which helps to better stop bleeding. The process of thrombus retraction is facilitated by thrombostenin - a contractive protein of blood platelets and fibrinogen in blood plasma. Over time, the clot undergoes fibrinolysis (or dissolution). The acceleration of blood clotting processes is called hypercoagulation, and the slowdown is called hypocoagulation.

5. Physiology of fibrinolysis

fibrinolysis system - an enzymatic system that breaks down fibrin strands, which were formed during blood coagulation, into soluble complexes. The fibrinolysis system is completely opposite to the blood coagulation system. Fibrinolysis limits the spread of blood coagulation through the vessels, regulates vascular permeability, restores their patency and ensures the liquid state of blood in the vascular bed. The fibrinolysis system includes the following components:

1) fibrinolysin (plasmin). It is found in an inactive form in the blood as profibrinolysin (plasminogen). It breaks down fibrin, fibrinogen, some plasma coagulation factors;

2) plasminogen activators (profibrinolysin). They belong to the globulin fraction of proteins. There are two groups of activators: direct action and indirect action. Direct-acting activators directly convert plasminogen into its active form - plasmin. Direct-acting activators - trypsin, urokinase, acid and alkaline phosphatase. Indirect-acting activators are in the blood plasma in an inactive state in the form of a proactivator. To activate it, tissue and plasma lysokinase is required. Some bacteria have lysokinase properties. There are tissue activators in the tissues, especially a lot of them are found in the uterus, lungs, thyroid gland, prostate;

3) inhibitors of fibrinolysis (antiplasmins) - albumins. Antiplasmins inhibit the action of the enzyme fibrinolysin and the conversion of profibrinolysin to fibrinolysin.

The process of fibrinolysis takes place in three phases.

During phase I, lysokinase, entering the bloodstream, brings the plasminogen proactivator into an active state. This reaction is carried out as a result of cleavage from the proactivator of a number of amino acids.

Phase II - the conversion of plasminogen into plasmin due to the cleavage of a lipid inhibitor under the action of an activator.

During phase III, under the influence of plasmin, fibrin is cleaved to polypeptides and amino acids. These enzymes are called fibrinogen / fibrin degradation products, they have a pronounced anticoagulant effect. They inhibit thrombin and inhibit the formation of prothrombinase, inhibit the process of fibrin polymerization, platelet adhesion and aggregation, enhance the effect of bradykinin, histamine, angiotensin on the vascular wall, which contributes to the release of fibrinolysis activators from the vascular endothelium.

Distinguish two types of fibrinolysis - enzymatic and non-enzymatic.

Enzymatic fibrinolysis carried out with the participation of the proteolytic enzyme plasmin. Fibrin is cleaved to degradation products.

Non-enzymatic fibrinolysis carried out by complex compounds of heparin with thrombogenic proteins, biogenic amines, hormones, conformational changes are made in the fibrin-S molecule.

The process of fibrinolysis goes through two mechanisms - external and internal.

Activation of fibrinolysis along the external pathway occurs due to tissue lysokinases, tissue plasminogen activators.

Proactivators and fibrinolysis activators are involved in the internal activation pathway, capable of converting proactivators into plasminogen activators or acting directly on the proenzyme and converting it into plasmin.

Leukocytes play a significant role in the process of fibrin clot dissolution due to their phagocytic activity. Leukocytes capture fibrin, lyse it and release its degradation products into the environment.

The process of fibrinolysis is considered in close connection with the process of blood coagulation. Their interconnections are carried out at the level of common pathways of activations in the reaction of the enzyme cascade, as well as due to neurohumoral mechanisms of regulation.

LECTURE No. 19. Physiology of the kidneys

1. Functions, significance of the urinary system

The excretion process is important for ensuring and maintaining the constancy of the internal environment of the body. The kidneys take an active part in this process, removing excess water, inorganic and organic substances, metabolic end products and foreign substances. The kidneys are a paired organ, one healthy kidney successfully maintains the stability of the internal environment of the body.

The kidneys perform a number of functions in the body.

1. They regulate the volume of blood and extracellular fluid (volume regulation), with an increase in blood volume, volomoreceptors of the left atrium are activated: secretion of antidiuretic hormone (ADH) is inhibited, urination increases, excretion of water and Na ions increases, which leads to the restoration of blood volume and extracellular fluid.

2. Osmoregulation is carried out - regulation of the concentration of osmotically active substances. With an excess of water in the body, the concentration of osmotically active substances in the blood decreases, which reduces the activity of the osmoreceptors of the supraoptic nucleus of the hypothalamus and leads to a decrease in the secretion of ADH and an increase in the release of water. With dehydration, osmoreceptors are excited, ADH secretion increases, water absorption in the tubules increases, and urine output decreases.

3. Regulation of ion exchange is carried out by reabsorption of ions in the renal tubules with the help of hormones. Aldosterone increases the reabsorption of Na ions, natriuretic hormone - reduces it. K secretion is enhanced by aldosterone and reduced by insulin.

4. Stabilize the acid-base balance. Normal blood pH is 7,36 and is maintained by a constant concentration of H ions.

5. Perform a metabolic function: participate in the metabolism of proteins, fats, carbohydrates. Reabsorption of amino acids provides material for protein synthesis. With prolonged fasting, the kidneys can synthesize up to 50% of the glucose produced in the body.

Fatty acids in the kidney cell are included in the composition of phospholipids and triglycerides.

6. Carry out an excretory function - the release of end products of nitrogen metabolism, foreign substances, excess organic substances that come with food or formed in the process of metabolism. The products of protein metabolism (urea, uric acid, creatinine, etc.) are filtered in the glomeruli, then reabsorbed in the renal tubules. All formed creatinine is excreted in the urine, uric acid undergoes significant reabsorption, urea - partial.

7. Perform an endocrine function - regulate erythropoiesis, blood coagulation, blood pressure due to the production of biologically active substances. The kidneys secrete biologically active substances: renin cleaves an inactive peptide from angiotensinogen, converts it into angiotensin I, which, under the action of an enzyme, passes into the active vasoconstrictor angiotensin II. Plasminogen activator (urokinase) increases urinary Na excretion. Erythropoietin stimulates erythropoiesis in the bone marrow, bradykinin is a powerful vasodilator.

The kidney is a homeostatic organ that takes part in maintaining the main indicators of the internal environment of the body.

2. The structure of the nephron

Nephron The functional unit of the kidney where urine is formed. The composition of the nephron includes:

1) renal corpuscle (double-walled capsule of the glomerulus, inside it is a glomerulus of capillaries);

2) proximal convoluted tubule (inside it there is a large number of villi);

3) the loop of Henley (descending and ascending parts), the descending part is thin, descends deep into the medulla, where the tubule bends 180 and goes into the cortical substance of the kidney, forming the ascending part of the nephron loop. The ascending part includes the thin and thick parts. It rises to the level of the glomerulus of its own nephron, where it passes into the next department;

4) distal convoluted tubule. This section of the tubule is in contact with the glomerulus between the afferent and efferent arterioles;

5) the final section of the nephron (short connecting tubule, flows into the collecting duct);

6) collecting duct (passes through the medulla and opens into the cavity of the renal pelvis).

There are the following segments of the nephron:

1) proximal (convoluted part of the proximal tubule);

2) thin (descending and thin ascending parts of the loop of Henley);

3) distal (thick ascending section, distal convoluted tubule and connecting tubule).

In the kidney, there are several types of nephrons:

1) superficial;

2) intracortical;

3) juxtamedullary.

The differences between them lie in their localization in the kidney.

Of great functional importance is the zone of the kidney in which the tubule is located. In the cortical substance there are renal glomeruli, proximal and distal tubules, connecting sections. In the outer strip of the medulla are the descending and thick ascending sections of the nephron loops, the collecting ducts. The inner medulla contains thin sections of nephron loops and collecting ducts. The location of each of the parts of the nephron in the kidney determines their participation in the activity of the kidney, in the process of urination.

The process of urine formation consists of three parts:

1) glomerular filtration, ultrafiltration of protein-free fluid from blood plasma into the capsule of the renal glomerulus, resulting in the formation of primary urine;

2) tubular reabsorption - the process of reabsorption of filtered substances and water from primary urine;

3) cell secretions. The cells of some departments of the tubule are transferred from the non-cellular fluid into the lumen of the nephron (secrete) a number of organic and inorganic substances, the molecules synthesized in the tubule cell are released into the lumen of the tubule.

The rate of urination depends on the general condition of the body, the presence of hormones, efferent nerves, or locally formed biologically active substances (tissue hormones).

3. Mechanism of tubular reabsorption

Reabsorption - the process of reabsorption of substances valuable to the body from primary urine. Various substances are absorbed in different parts of the tubules of the nephron. In the proximal section, amino acids, glucose, vitamins, proteins, microelements, a significant amount of Na, Cl ions are completely reabsorbed. In subsequent departments, mainly electrolytes and water are reabsorbed.

Reabsorption in the tubules is provided by active and passive transport.

Active transport - reabsorption - is carried out against an electrochemical and concentration gradient. There are two types of active transport:

1) primary active;

2) secondary-active.

Primary active transport is carried out when a substance is transferred against an electrochemical gradient due to the energy of cellular metabolism. The transport of Na ions occurs with the participation of the enzymes sodium-, potassium-ATPase, and the energy of ATP is used.

Secondary active transport transports a substance against a concentration gradient without expending energy, so glucose and amino acids are reabsorbed. From the lumen of the tubule, they enter the cells of the proximal tubule with the help of a carrier, which must attach the Na ion. This complex promotes the movement of a substance through the cell membrane and its entry into the cell. The driving force of the carrier is the lower concentration of Na ions in the cytoplasm of the cell compared to the lumen of the tubule. The concentration gradient of Na is due to the active excretion of Na from the cell with the help of sodium-, potassium-ATP-ase.

Reabsorption of water, chlorine, some ions, and urea is carried out using passive transport - along an electrochemical, concentration or osmotic gradient. Using passive transport in the distal convoluted tubule, Cl ion is absorbed along an electrochemical gradient, which is created by active transport of Na ions.

To characterize the absorption of various substances in the renal tubules, the excretion threshold is of great importance. Non-threshold substances are released at any concentration in the blood plasma. The excretion threshold for physiologically important substances of the body is different, the excretion of glucose in the urine occurs if its concentration in the blood plasma and in the glomerular filtrate exceeds 10 mmol / l.

LECTURE No. 20. Physiology of the digestive system

1. The concept of the digestive system. Its functions

Digestive system - a complex physiological system that ensures the digestion of food, the absorption of nutrients and the adaptation of this process to the conditions of existence.

The digestive system includes:

1) the entire gastrointestinal tract;

2) all digestive glands;

3) mechanisms of regulation.

The gastrointestinal tract begins with the oral cavity, continues with the esophagus, stomach and ends with the intestines. The glands are located throughout the digestive tube and secrete secrets into the lumen of the organs.

All functions are divided into digestive and non-digestive. Digestives include:

1) secretory activity of the digestive glands;

2) motor activity of the gastrointestinal tract (due to the presence of smooth muscle cells and skeletal muscles that provide mechanical processing and promotion of food);

3) absorption function (the entry of end products into the blood and lymph).

Non-Digestive Functions:

1) endocrine;

2) excretory;

3) protective;

4) activity of microflora.

The endocrine function is carried out due to the presence in the gastrointestinal tract of individual cells that produce hormones - hormones.

The excretory role is to excrete undigested food products formed during metabolic processes.

Protective activity is due to the presence of non-specific resistance of the body, which is provided due to the presence of macrophages and lysozyme secretions, as well as due to acquired immunity. Lymphoid tissue also plays an important role (tonsils of the pharyngeal ring of Pirogov, Peyer's patches or solitary follicles of the small intestine, appendix, individual plasma cells of the stomach), which releases lymphocytes and immunoglobulins into the lumen of the gastrointestinal tract. Lymphocytes provide tissue immunity. Immunoglobulins, especially group A, are not exposed to the activity of proteolytic enzymes of the digestive juice, prevent the fixation of food antigens on the mucous membrane and contribute to their recognition, forming a certain response of the body.

The activity of microflora is associated with the presence of aerobic bacteria (10%) and anaerobic (90%) in the composition. They break down plant fibers (cellulose, hemicellulose, etc.) to fatty acids, participate in the synthesis of vitamins K and group B, inhibit the processes of decay and fermentation in the small intestine, and stimulate the body's immune system. Negative is the formation during lactic acid fermentation of indole, skatole and phenol.

Thus, the digestive system provides mechanical and chemical processing of food, absorbs end products of decay into the blood and lymph, transports nutrients to cells and tissues, and performs energy and plastic functions.

2. Types of digestion

There are three types of digestion:

1) extracellular;

2) intracellular;

3) membrane.

Extracellular digestion occurs outside the cell, which synthesizes enzymes. In turn, it is divided into cavitary and extracavitary. With cavity digestion, enzymes act at a distance, but in a certain cavity (for example, this is the secretion of salivary glands into the oral cavity). Extracavitary is carried out outside the body in which enzymes are formed (for example, a microbial cell secretes a secret into the environment).

Membrane (parietal) digestion was described in the 30s. XVIII century A. M. Ugolev. It occurs at the border between extracellular and intracellular digestion, i.e., on the membrane. In humans, it occurs in the small intestine, since there is a brush border there. It is formed by microvilli - these are microgrowths of the enterocyte membrane approximately 1-1,5 microns long and up to 0,1 microns wide. Up to several thousand microvilli can form on the membrane of 1 cell. Thanks to this structure, the contact area (more than 40 times) of the intestine with its contents increases. Features of membrane digestion:

1) carried out by enzymes of dual origin (synthesized by cells and absorbed by intestinal contents);

2) enzymes are fixed on the cell membrane in such a way that the active center is directed into the cavity;

3) occurs only under sterile conditions;

4) is the final stage in food processing;

5) brings together the process of splitting and absorption due to the fact that the end products are carried on transport proteins.

In the human body, cavity digestion ensures the breakdown of 20-50% of food, and membrane digestion - 50-80%.

3. Secretory function of the digestive system

The secretory function of the digestive glands is to release secretions into the lumen of the gastrointestinal tract that take part in food processing. For their formation, cells must receive certain amounts of blood, which carries all the necessary substances. The secretions of the gastrointestinal tract are digestive juices. Any juice consists of 90-95% water and dry matter. The dry residue includes organic and inorganic substances. Among the inorganic ones, the largest volume is occupied by anions and cations, and hydrochloric acid. Organic presented:

1) enzymes (the main component is proteolytic enzymes that break down proteins into amino acids, polypeptides and individual amino acids, glucolytic enzymes convert carbohydrates to di- and monosaccharides, lipolytic enzymes convert fats into glycerol and fatty acids);

2) lysine. The main component of mucus, which gives viscosity and promotes the formation of a food bolus (boleos), in the stomach and intestines interacts with bicarbonates of gastric juice and forms a mucosa-bicarbonate complex that lines the mucous membrane and protects it from self-digestion;

3) substances that have a bactericidal effect (for example, muropeptidase);

4) substances that must be removed from the body (for example, nitrogen-containing substances - urea, uric acid, creatinine, etc.);

5) specific components (these are bile acids and pigments, the internal factor of Castle, etc.).

The composition and quantity of digestive juices is influenced by the diet.

Regulation of secretory function is carried out in three ways - nervous, humoral, local.

Reflex mechanisms are the separation of digestive juices according to the principle of conditioned and unconditioned reflexes.

Humoral mechanisms include three groups of substances:

1) hormones of the gastrointestinal tract;

2) hormones of endocrine glands;

3) biologically active substances.

Gastrointestinal hormones are simple peptides produced by the cells of the APUD system. Most act in an endocrine way, but some of them act in a para-endocrine way. Entering the intercellular spaces, they act on nearby cells. For example, the hormone gastrin is produced in the pyloric part of the stomach, the duodenum and the upper third of the small intestine. It stimulates the secretion of gastric juice, especially hydrochloric acid and pancreatic enzymes. Bambezin is formed in the same place and is an activator for the synthesis of gastrin. Secretin stimulates the secretion of pancreatic juice, water and inorganic substances, inhibits the secretion of hydrochloric acid, and has little effect on other glands. Cholecystokinin-pancreosinin causes the separation of bile and its entry into the duodenum. The inhibitory effect is exerted by hormones:

1) grocery store;

2) a gastro-inhibiting polypeptide;

3) pancreatic polypeptide;

4) vasoactive intestinal polypeptide;

5) enteroglucagon;

6) somatostatin.

Among biologically active substances, serotonin, histamine, kinins, etc. have an intensifying effect. Humoral mechanisms appear in the stomach and are most pronounced in the duodenum and in the upper part of the small intestine.

Local regulation is carried out:

1) through the metsympathetic nervous system;

2) through the direct effect of food gruel on secretory cells.

Coffee, spicy substances, alcohol, liquid food, etc. also have a stimulating effect. Local mechanisms are most pronounced in the lower sections of the small intestine and in the large intestine.

4. Motor activity of the gastrointestinal tract

Motor activity is a coordinated work of the smooth muscles of the gastrointestinal tract and special skeletal muscles. They lie in three layers and consist of circularly arranged muscle fibers, which gradually pass into longitudinal muscle fibers and end in the submucosal layer. Skeletal muscles include chewing and other muscles of the face.

The value of motor activity:

1) leads to mechanical breakdown of food;

2) promotes the promotion of contents through the gastrointestinal tract;

3) provides opening and closing of sphincters;

4) affects the evacuation of digested nutrients.

There are several types of abbreviations:

1) peristaltic;

2) non-peristaltic;

3) antiperistaltic;

4) hungry.

Peristaltic refers to strictly coordinated contractions of the circular and longitudinal layers of muscles.

Circular muscles contract behind the content, and longitudinal muscles in front of it. This type of contraction is typical for the esophagus, stomach, small and large intestines. Mass peristalsis and emptying are also present in the thick section. Mass peristalsis occurs as a result of the simultaneous contraction of all smooth muscle fibers.

Non-peristaltic contractions are the coordinated work of skeletal and smooth muscle muscles. There are five types of movements:

1) sucking, chewing, swallowing in the oral cavity;

2) tonic movements;

3) systolic movements;

4) rhythmic movements;

5) pendulum movements.

Tonic contractions are a state of moderate tension in the smooth muscles of the gastrointestinal tract. The value lies in the change in tone in the process of digestion. For example, when eating, there is a reflex relaxation of the smooth muscles of the stomach in order for it to increase in size. They also contribute to adaptation to different volumes of incoming food and lead to the evacuation of contents by increasing pressure.

Systolic movements occur in the antrum of the stomach with the contraction of all layers of the muscles. As a result, food is evacuated into the duodenum. Most of the contents are pushed out in the opposite direction, which contributes to better mixing.

Rhythmic segmentation is characteristic of the small intestine and occurs when the circular muscles contract for 1,5-2 cm every 15-20 cm, i.e. the small intestine is divided into separate segments, which appear in a different place after a few minutes. This type of movement ensures the mixing of the contents along with the intestinal juices.

Pendulum contractions occur when the circular and longitudinal muscle fibers are stretched. Such contractions are characteristic of the small intestine and lead to mixing of food.

Non-peristaltic contractions provide grinding, mixing, promotion and evacuation of food.

Antiperistaltic movements occur when the circular muscles in front and the longitudinal muscles behind the food bolus contract. They are directed from the distal to the proximal, i.e., from bottom to top, and lead to vomiting. The act of vomiting is the removal of contents through the mouth. It occurs when the complex food center of the medulla oblongata is excited, which occurs due to reflex and humoral mechanisms. The significance lies in the movement of food due to protective reflexes.

Hunger contractions appear with a long absence of food every 45-50 minutes. Their activity leads to the emergence of eating behavior.

5. Regulation of motor activity of the gastrointestinal tract

A feature of motor activity is the ability of some cells of the gastrointestinal tract to undergo rhythmic spontaneous depolarization. This means that they can be rhythmically excited. The result is weak shifts in membrane potential - slow electrical waves. Since they do not reach a critical level, smooth muscle contraction does not occur, but fast voltage-gated calcium channels open. Ca ions move into the cell and generate an action potential, leading to contraction. After the termination of the action potential, the muscles do not relax, but are in a state of tonic contraction. This is explained by the fact that after the action potential the slow voltage-gated Na and Ca channels remain open.

There are also chemosensitive channels in smooth muscle cells, which are torn off when receptors interact with any biologically active substances (for example, mediators).

This process is regulated by three mechanisms:

1) reflex;

2) humoral;

3) local.

The reflex component causes inhibition or activation of motor activity when receptors are excited. The parasympathetic department increases motor function: for the upper part - the vagus nerves, for the lower part - the pelvic nerves. The inhibitory effect is exerted by the celiac plexus of the sympathetic nervous system. When the underlying part of the gastrointestinal tract is activated, the higher part is inhibited. There are three reflexes in reflex regulation:

1) gastroenteric (when the receptors of the stomach are excited, other departments are activated);

2) entero-enteral (have both inhibitory and excitatory effects on the underlying departments);

3) recto-enteral (when the rectum is filled, inhibition occurs).

Humoral mechanisms predominate mainly in the duodenum and the upper third of the small intestine.

The excitatory effect is exerted by:

1) motilin (produced by cells of the stomach and duodenum, has an activating effect on the entire gastrointestinal tract);

2) gastrin (stimulates gastric motility);

3) bambezin (causes the separation of gastrin);

4) cholecystokinin-pancreosinin (provides general excitation);

5) secretin (activates the motor, but inhibits contractions in the stomach).

Braking effect is exerted by:

1) vasoactive intestinal polypeptide;

2) a gastro-inhibiting polypeptide;

3) somatostatin;

4) enteroglucagon.

Endocrine gland hormones also affect motor function. So, for example, insulin stimulates it, and adrenaline slows it down.

local arrangements are carried out due to the presence of the metsympathetic nervous system and prevail in the small and large intestines. The stimulating effect is:

1) coarse undigested foods (fiber);

2) hydrochloric acid;

3) saliva;

4) the end products of the breakdown of proteins and carbohydrates.

Inhibitory action occurs in the presence of lipids.

Thus, the basis of motor activity is the ability to generate slow electrical waves.

6. The mechanism of the sphincters

Sphincter - thickening of smooth muscle layers, due to which the entire gastrointestinal tract is divided into certain departments. There are the following sphincters:

1) cardiac;

2) pyloric;

3) iliocyclic;

4) internal and external sphincter of the rectum.

The opening and closing of sphincters is based on a reflex mechanism, according to which the parasympathetic department opens the sphincter, and the sympathetic department closes it.

The cardiac sphincter is located at the junction of the esophagus with the stomach. When a food bolus enters the lower parts of the esophagus, mechanoreceptors are excited. They send impulses along the afferent fibers of the vagus nerves to the complex food center of the medulla oblongata and return along the efferent pathways to the receptors, causing the opening of the sphincters. As a result, the food bolus enters the stomach, which leads to the activation of gastric mechanoreceptors, which send impulses along the fibers of the vagus nerves to the complex food center of the medulla oblongata. They have an inhibitory effect on the nuclei of the vagus nerves, and under the influence of the sympathetic department (fibers of the celiac trunk), the sphincter closes.

The pyloric sphincter is located on the border between the stomach and the duodenum. Its work includes another component that has an exciting effect - hydrochloric acid. It acts on the antrum of the stomach. When the contents enter the stomach, chemoreceptors are excited. Impulses are sent to the complex food center in the medulla oblongata, and the sphincter opens. Since the intestines are alkaline, when acidified food enters the duodenum, chemoreceptors are excited. This leads to the activation of the sympathetic division and the closure of the sphincter.

The mechanism of operation of the remaining sphincters is similar to the principle of the cardiac.

The main function of the sphincters is the evacuation of contents, which not only promotes opening and closing, but also leads to an increase in the tone of the smooth muscles of the gastrointestinal tract, systolic contractions of the antrum of the stomach, and an increase in pressure.

Thus, motor activity contributes to better digestion, promotion and removal of products from the body.

7. Physiology of absorption

Suction - the process of transferring nutrients from the cavity of the gastrointestinal tract into the internal environment of the body - blood and lymph. Absorption occurs throughout the gastrointestinal tract, but its intensity is variable and depends on three reasons:

1) the structure of the mucous membrane;

2) availability of final products;

3) the time spent by the contents in the cavity.

The mucous membrane of the lower part of the tongue and the bottom of the oral cavity is thinned, but is capable of absorbing water and minerals. Due to the short duration of food in the esophagus (approximately 5-8 s), absorption does not occur. In the stomach and duodenum, a small amount of water, minerals, monosaccharides, peptones and polypeptides, medicinal components, and alcohol are absorbed.

The main amount of water, minerals, end products of the breakdown of proteins, fats, carbohydrates, medicinal components is absorbed in the small intestine. This is due to a number of morphological features of the structure of the mucous membrane, due to which the contact area with the presence of folds, villi and microvilli increases significantly). Each villus is covered with a single-layer cylindrical epithelium, which has a high degree of permeability.

In the center is a network of lymphoid and blood capillaries belonging to the class of fenestrated. They have pores through which nutrients pass. The connective tissue also contains smooth muscle fibers that provide movement to the villi. It can be forced and oscillatory. The metsympathetic nervous system innervates the mucous membrane.

In the large intestine, stool is formed. The mucosa of this department has the ability to absorb nutrients, but this does not happen, since normally they are absorbed in the overlying structures.

8. Mechanism of absorption of water and minerals

Absorption is carried out due to physico-chemical mechanisms and physiological patterns. This process is based on active and passive modes of transport. Of great importance is the structure of enterocytes, since absorption occurs differently through the apical, basal and lateral membranes.

Studies have shown that absorption is an active process of enterocyte activity. In the experiment, monoiodoacetic acid was introduced into the lumen of the gastrointestinal tract, which causes the death of intestinal cells. This led to a sharp decrease in the intensity of absorption. This process is characterized by the transport of nutrients in two directions and selectivity.

Water absorption is carried out throughout the gastrointestinal tract, but most intensively in the small intestine. The process proceeds passively in two directions due to the presence of an osmotic gradient, which is created during the movement of Na, Cl and glucose. During a meal containing a large amount of water, water from the intestinal lumen enters the internal environment of the body. Conversely, when hyperosmotic food is consumed, water from the blood plasma is released into the intestinal cavity. About 8-9 liters of water are absorbed per day, of which about 2,5 liters comes from food, and the rest is part of the digestive juices.

Absorption of Na, as well as water, occurs in all sections, but most intensively in the large intestine. Na penetrates through the apical membrane of the brush border, which contains a transport protein - passive transport. And through the basement membrane, active transport occurs - movement along an electrochemical concentration gradient.

Transport of Cl is associated with Na and is also directed along the electrochemical concentration gradient of Na contained in the internal environment.

The absorption of bicarbonates is based on the intake of H ions from the internal environment during the transport of Na. H ions react with bicarbonates and form carbonic acid. Under the influence of carbonic anhydrase, the acid decomposes into water and carbon dioxide. Further, absorption into the internal environment continues passively, the release of the formed products occurs through the lungs during breathing.

Absorption of divalent cations is much more difficult. The most easily transported Ca. At low concentrations, cations pass into enterocytes with the help of calcium-binding protein by facilitated diffusion. From the intestinal cells, it enters the internal environment with the help of active transport. At high concentrations, cations are absorbed by simple diffusion.

Iron enters the enterocyte by active transport, during which a complex of iron and ferritin protein is formed.

9. Mechanisms of absorption of carbohydrates, fats and proteins

Absorption of carbohydrates occurs in the form of metabolic end products (mono- and disaccharides) in the upper third of the small intestine. Glucose and galactose are absorbed by active transport, and the absorption of glucose is associated with Na ions - symport. Mannose and pentose enter passively along the glucose concentration gradient. Fructose is supplied by facilitated diffusion. The absorption of glucose into the blood occurs most intensively.

Protein absorption occurs most intensively in the upper parts of the small intestine, with proteins of animal origin accounting for 90-95%, and proteins of plant origin - 60-70%. The main breakdown products that are formed as a result of metabolism are amino acids, polypeptides, and peptones. Transport of amino acids requires the presence of carrier molecules. Four groups of transport proteins have been identified that provide an active absorption process. The absorption of polypeptides occurs passively along a concentration gradient. Products enter directly into the internal environment and are carried throughout the body through the bloodstream.

The rate of absorption of fats is much slower; absorption is most active in the upper parts of the small intestine. Transport of fats is carried out in the form of two forms - glycerol and fatty acids consisting of long chains (oleic, stearic, palmitic, etc.). Glycerol enters passively into enterocytes. Fatty acids form micelles with bile acids and only in this form are sent to the membrane of intestinal cells. Here the complex disintegrates: fatty acids dissolve in the lipids of the cell membrane and pass into the cell, and bile acids remain in the intestinal cavity. Active synthesis of lipoproteins (chylomicron) and very low density lipoproteins begins inside the enterocytes. These substances then enter the lymphatic vessels through passive transport. The level of lipids with short and medium chains is low. Therefore, they are absorbed almost unchanged into enterocytes by simple diffusion, where, under the action of esterases, they are broken down into final products and take part in the synthesis of lipoproteins. This method of transport requires less cost, so in some cases, when the gastrointestinal tract is overloaded, this type of absorption is activated.

Thus, the process of absorption proceeds according to the mechanism of active and passive transport.

10. Mechanisms of regulation of absorption processes

The normal function of the cells of the mucous membrane of the gastrointestinal tract is regulated by neurohumoral and local mechanisms.

In the small intestine, the main role belongs to the local method, since intramural plexuses have a great influence on the activity of organs. They innervate the villi. Due to this, the area of interaction of the food gruel with the mucous membrane increases, which increases the intensity of the absorption process. The local action is activated in the presence of end products of the breakdown of substances and hydrochloric acid, as well as in the presence of liquids (coffee, tea, soup).

Humoral regulation occurs due to the hormone of the gastrointestinal tract villikinin. It is produced in the duodenum and stimulates the movement of the villi. The intensity of absorption is also affected by secretin, gastrin, cholecystokinin-pancreosinin. Not the last role is played by the hormones of the endocrine glands. Thus, insulin stimulates, and adrenaline inhibits transport activity. Among the biologically active substances, serotonin and histamine provide absorption.

The reflex mechanism is based on the principles of an unconditioned reflex, i.e., stimulation and inhibition of processes occur with the help of the parasympathetic and sympathetic divisions of the autonomic nervous system.

Thus, the regulation of absorption processes is carried out using reflex, humoral and local mechanisms.

11. Physiology of the digestive center

The first ideas about the structure and functions of the food center were summarized by I. P. Pavlov in 1911. According to modern ideas, the food center is a set of neurons located at different levels of the central nervous system, the main function of which is to regulate the activity of the digestive system and ensure adaptation to the needs of the body . Currently the following levels are allocated:

1) spinal;

2) bulbar;

3) hypothalamic;

4) cortical.

The spinal component is formed by the nerve cells of the lateral horns of the spinal cord, which provide innervation to the entire gastrointestinal tract and digestive glands. It has no independent significance and is subject to impulses from overlying departments. The bulbar level is represented by neurons of the reticular formation of the medulla oblongata, which are part of the nuclei of the trigeminal, facial, glossopharyngeal, vagus and hypoglossal nerves. The combination of these nuclei forms a complex food center of the medulla oblongata, which regulates the secretory, motor and absorption function of the entire gastrointestinal tract.

The nuclei of the hypothalamus provide certain forms of eating behavior. For example, the lateral nuclei constitute the center of hunger or nutrition. When neurons are irritated, bulimia occurs - gluttony, and when they are destroyed, the animal dies from a lack of nutrients. The ventromedial nuclei form the saturation center. When they are activated, the animal refuses food, and vice versa. The perifornical nuclei belong to the thirst center; when irritated, the animal constantly requires water. The importance of this department is to ensure various forms of eating behavior.

The cortical level is represented by neurons that are part of the brain department of the gustatory and olfactory sensory systems. In addition, separate point foci were found in the frontal lobes of the cerebral cortex, which are involved in the regulation of digestion processes. According to the principle of a conditioned reflex, a more perfect adaptation of the organism to the conditions of existence is achieved.

12. Physiology of hunger, appetite, thirst, satiety

Hunger - a state of the body that occurs during a long absence of food, as a result of excitation of the lateral nuclei of the hypothalamus. The feeling of hunger is characterized by two manifestations:

1) objective (occurrence of hunger contractions of the stomach, leading to food-procuring behavior);

2) subjective (discomfort in the epigastric region, weakness, dizziness, nausea).

Currently, there are two theories explaining the mechanisms of excitation of hypothalamic neurons:

1) the theory of "hungry blood";

2) "peripheral" theory.

The theory of "hungry blood" was developed by IP Chukichev. Its essence lies in the fact that when the blood of a hungry animal is transfused into a well-fed animal, the latter develops food-procuring behavior (and vice versa). "Hungry blood" activates the neurons of the hypothalamus due to low concentrations of glucose, amino acids, lipids, etc.

There are two ways of influence:

1) reflex (through chemoreceptors of the reflexogenic zones of the cardiovascular system);

2) humoral (nutrient-poor blood flows to the neurons of the hypothalamus and causes their excitation).

According to the "peripheral" theory, hunger contractions of the stomach are transmitted to the lateral nuclei and lead to their activation.

Appetite - craving for food, emotional sensations associated with eating. It occurs at the level of the cerebral cortex according to the principle of a conditioned reflex and not always in response to a state of hunger, and sometimes to a decrease in the level of nutrients in the blood (mainly glucose). The appearance of a feeling of appetite is associated with the release of a large amount of digestive juices containing a high level of enzymes.

Saturation occurs when the feeling of hunger is satisfied, accompanied by excitation of the ventromedial nuclei of the hypothalamus according to the principle of an unconditioned reflex. There are two types of manifestations:

1) objective (cessation of food-producing behavior and hunger contractions of the stomach);

2) subjective (the presence of pleasant sensations).

Currently, two saturation theories have been developed:

1) primary sensory;

2) secondary or true.

The primary theory is based on stimulation of the gastric mechanoreceptors. Proof: in experiments, when a canister is introduced into the stomach of an animal, saturation occurs in 15-20 minutes, accompanied by an increase in the level of nutrients taken from the depositing organs.

According to the secondary (or metabolic) theory, true saturation occurs only 1,5-2 hours after a meal. As a result, the level of nutrients in the blood increases, leading to the excitation of the ventromedial nuclei of the hypothalamus. Due to the presence of reciprocal relationships in the cerebral cortex, inhibition of the lateral nuclei of the hypothalamus is observed.

Thirst - the state of the body that occurs in the absence of water. It occurs:

1) upon excitation of the perifornical nuclei during a decrease in fluid due to the activation of volomoreceptors;

2) with a decrease in the volume of liquid (there is an increase in osmotic pressure, to which osmotic and sodium-dependent receptors react);

3) when the mucous membranes of the oral cavity dry up;

4) with local warming of hypothalamic neurons.

Distinguish between true and false desire. True thirst appears when the level of fluid in the body decreases and is accompanied by a desire to drink. False thirst is accompanied by drying of the oral mucosa.

Thus, the food center regulates the activity of the digestive system and provides various forms of food-procuring behavior for human and animal organisms.

Authors: Kuzina S.I., Firsova S.S.

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