Histology. General principles of tissue organization

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Histology. General principles of tissue organization

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Topic 8. GENERAL PRINCIPLES OF TISSUE ORGANIZATION

Tissue is a historically (phylogenetically) established system of cells and non-cellular structures that has a common structure, and sometimes origin, and is specialized in performing certain functions. Tissue is a new (after cells) level of organization of living matter.

Structural components of tissue: cells, cell derivatives, intercellular substance.

Characterization of the structural components of the tissue

Cells are the main, functionally leading components of tissues. Almost all tissues are composed of several types of cells. In addition, cells of each type in tissues can be at different stages of maturity (differentiation). Therefore, in tissue, such concepts as cell population and cell differon are distinguished.

A cell population is a collection of cells of a given type. For example, loose connective tissue (the most common in the body) contains:

1) population of fibroblasts;

2) population of macrophages;

3) population of tissue basophils, etc.

Cellular differon (or histogenetic series) is a collection of cells of a given type (a given population) that are at different stages of differentiation. The initial cells of differon are stem cells, followed by young (blast) cells, maturing cells and mature cells. Distinguish between complete differon or incomplete, depending on whether there are cells of all types of development in the tissues.

However, tissues are not just an accumulation of various cells. Cells in tissues are in a certain relationship, and the function of each of them is aimed at performing the function of the tissue.

Cells in tissues influence each other either directly through gap-like junctions (nexuses) and synapses, or at a distance (remotely) through the release of various biologically active substances.

Cell derivatives:

1) symplasts (fusion of individual cells, for example, muscle fiber);

2) syncytium (several cells interconnected by processes, for example, the spermatogenic epithelium of the convoluted tubules of the testis);

3) postcellular formations (erythrocytes, platelets).

The intercellular substance is also a product of the activity of certain cells. The intercellular substance consists of:

1) an amorphous substance;

2) fibers (collagen, reticular, elastic).

The intercellular substance is not equally expressed in different tissues.

Development of tissues in ontogenesis (embryogenesis) and phylogenesis

In ontogenesis, the following stages of tissue development are distinguished:

1) the stage of orthotopic differentiation. At this stage, the rudiments of future specific tissues are localized first in certain areas of the egg and then in the zygote;

2) stage of blastomeric differentiation. As a result of zygote cleavage, presumptive (supposed) tissue rudiments are localized in different blastomeres of the embryo;

3) the stage of rudimentary differentiation. As a result of gastrulation, presumptive tissue rudiments are localized in certain areas of the germ layers;

4) histogenesis. This is the process of transformation of the rudiments of tissues and tissues as a result of proliferation, growth, induction, determination, migration and differentiation of cells.

There are several theories of tissue development in phylogenesis:

1) the law of parallel series (A. A. Zavarzin). Animal and plant tissues of different species and classes that perform the same functions have a similar structure, that is, they develop in parallel in animals of different phylogenetic classes;

2) the law of divergent evolution (N. G. Khlopin). In phylogeny, there is a divergence of tissue characteristics and the emergence of new tissue varieties within the tissue group, which leads to the complication of animal organisms and the emergence of a variety of tissues.

Fabric classifications

There are several approaches to the classification of tissues. The morphofunctional classification is generally accepted, according to which four tissue groups are distinguished:

1) epithelial tissues;

2) connective tissues (tissues of the internal environment, musculoskeletal tissues);

3) muscle tissue;

4) nervous tissue.

Tissue homeostasis (or maintaining the structural constancy of tissues)

The state of the structural components of tissues and their functional activity are constantly changing under the influence of external factors. First of all, rhythmic fluctuations in the structural and functional state of tissues are noted: biological rhythms (daily, weekly, seasonal, annual). External factors can cause adaptive (adaptive) and maladaptive changes, leading to the disintegration of tissue components. There are regulatory mechanisms (interstitial, intertissue, organismal) that ensure the maintenance of structural homeostasis.

Interstitial regulatory mechanisms are provided, in particular, by the ability of mature cells to secrete biologically active substances (keylons), which inhibit the reproduction of young (stem and blast) cells of the same population. With the death of a significant part of mature cells, the release of chalones decreases, which stimulates proliferative processes and leads to the restoration of the number of cells in this population.

Interstitial regulatory mechanisms are provided by inductive interaction, primarily with the participation of lymphoid tissue (immune system) in maintaining structural homeostasis.

Organismic regulatory factors are provided by the influence of the endocrine and nervous systems.

Under some external influences, the natural determination of young cells can be disrupted, which can lead to the transformation of one tissue type into another. This phenomenon is called "metaplasia" and occurs only within a given tissue group. For example, the replacement of a single-layer prismatic epithelium of the stomach with a single-layer flat.

Tissue regeneration

Regeneration is the restoration of cells, tissues and organs, aimed at maintaining the functional activity of this system. In regeneration, such concepts as the form of regeneration, the level of regeneration, and the method of regeneration are distinguished.

Forms of regeneration:

1) physiological regeneration - restoration of tissue cells after their natural death (for example, hematopoiesis);

2) reparative regeneration - restoration of tissues and organs after their damage (trauma, inflammation, surgical interventions, etc.).

Regeneration levels:

1) cellular (intracellular);

2) tissue;

3) organ.

Regeneration methods:

1) cellular;

2) intracellular;

3) substitution.

Factors regulating regeneration:

1) hormones;

2) mediators;

3) keylons;

4) growth factors, etc.

Tissue Integration

Tissues, being one of the levels of organization of living matter, are part of the structures of a higher level of organization of living matter - the structural and functional units of organs and the composition of organs in which integration (combination) of several tissues occurs.

Integration mechanisms:

1) intertissue (usually inductive) interactions;

2) endocrine influences;

3) nervous influences.

For example, the composition of the heart includes cardiac muscle tissue, connective tissue, epithelial tissue.

Authors: Selezneva T.D., Mishin A.S., Barsukov V.Yu.

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