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Lecture notes, cheat sheets
Histology. Reproductive system
Directory / Lecture notes, cheat sheets Table of contents (expand) Topic 25. REGENERAL SYSTEM Development of the sex organs The sources of development of the genital organs are the genital ridges and primary germ cells. Sexual (or gonadal) ridges are indifferent gonads, the rudiments of future sexual future organs (both male and female) - testicles and ovaries. Sexual rollers are formed already at the 4th week of intrauterine development, however, at this time it is impossible to identify male or female rudiments. After laying the indifferent gonads are populated by the primary germ cells of the cortex and medulla. Primary sex cells are formed in the wall of the yolk sac, after which they migrate to the sex gonads. After migration and sexual differentiation, the primary germ cells, under the influence of certain factors, turn into spermatogonia in the testicles and into oogonia in the ovaries. However, for the final differentiation into spermatozoa and eggs, germ cells must go through the stages of reproduction, growth, maturation and formation. Until the 8th week of intrauterine development, it is impossible to find differences in the male and female genital organs. 45 - 50th day (8 weeks) - a critical period in the development of the embryo, it is at this time that sexual differentiation occurs. During fertilization, chromosomal determination occurs, while the Y chromosome ensures the subsequent genetic development of the male. The Y chromosome encodes the regulatory factor TDF, one of the inducers of the male reproductive system, a factor that determines the development of male gonads. Under the influence of the TDF factor, the testicles develop from the primary gonads, and the development of further sexual structures is provided by male sex hormones and the Müllerian inhibitory factor, also produced in the testicles. The indifferent gonads consist of cortex and medulla. In the female body, the cortical substance develops in the gonads, and the male substance atrophies; in the male body, on the contrary, the cortical substance atrophies, and the medullary substance develops. At the 8th week of embryogenesis, the testicles are located at the level of the upper lumbar vertebrae, and a supporting ligament stretches from their lower pole, which stretches down and acts as a conductor for the testicles from the abdominal cavity to the scrotum. The final descent of the testicles occurs by the end of the 1st month of life. The extragonadal genital ducts originate from the mesonephric (Wolffian) and paramesonephric (Müllerian) ducts, the external genital organs differentiate from the urogenital sinus, genital tubercle and genital ridges. The primary kidney of the embryo is drained by the mesonephric (or wolffian) duct. In boys, under the influence of the male sex hormone testosterone, it forms the testicular network, epididymis, seminal vesicles and vas deferens. In women, due to a different hormonal background, these ducts are obliterated. In the testicles of boys, there are Sertoli cells that synthesize the Müllerian inhibitory factor. It leads to obliteration and regression of the paramesonephric (or Müllerian) ducts. The paramesonephric duct (or female duct) is a thin tube that runs parallel to the mesonephric duct along the primary kidney. In the proximal (cranial) section, the paramesonephric ducts run separately, parallel to each other, and in the distal (or caudal) section they merge and open into the urogenital sinus. The cranial section of the paramesonephric ducts differentiates into the fallopian tubes and uterus, and the caudal section into the upper part of the vagina. Differentiation is carried out in the absence of the Müllerian inhibitory factor, regardless of whether female sex (ovarian) hormones are present or not. In the male body, under the influence of the Müllerian inhibitory factor, the paramesonephric ducts undergo degeneration. Differentiation of the external genital organs is carried out from the urogenital sinus, genital tubercle, genital folds and genital folds. The development of the external genital organs is determined by sex hormones. In boys, under the influence of testosterone, the prostate gland and bulbourethral glands develop from the urogenital sinus. The formation of other external genital organs - the penis and scrotum is carried out under the influence of dihydrotestosterone at the 12th - 14th week of intrauterine development. The development of the external genital organs according to the female type occurs in the absence of male sex hormones (androgens). The genitourinary sinus gives rise to the lower part of the vagina, the genital tubercle turns into the clitoris, and the genital ridges and genital folds into the labia majora and labia minora. Gametogenesis Spermatogenesis The process of formation of male germ cells goes through four stages - reproduction, growth, maturation and formation. Stage of reproduction and growth. After formation, the primary germ cells migrate to the rudiments of the gonads, where they divide and differentiate into spermatogonia. In the spermatogonia stage, the germ cells are at rest until the period of sexual reproduction. Under the influence of male sex hormones and, above all, testosterone, the reproduction of spermatogonia begins. Testosterone is synthesized by Leydig cells. Their activity, in turn, is regulated by the hypothalamus, where gonadoliberins are synthesized, which activate the secretion of gonadotropic hormones of the adenohypophysis, which affect the secretion of Leydig cells. At the stage of reproduction, there are two types of spermatogonia - A and B. Type A spermatogonia differ in the degree of chromatin condensation into light and dark. Dark spermatogonia are reservoir cells and rarely enter mitosis, light spermatogonia are semi-stem cells, they constantly and very actively divide, and interphase is replaced by mitosis. Mitosis of type A clear cells can proceed symmetrically (with the formation of two type B spermatogonia) and asymmetrically, in which one type B spermatogonium and one type A clear cell are formed. Type B spermatogonia have a round nucleus and condensed chromatin. They enter mitosis, but at the same time remain connected to each other with the help of cytoplasmic bridges. After passing through several successive mitotic divisions, type B spermatogonia differentiate into first-order spermatocytes. First-order spermatocytes move from the basal space to the adluminal space and enter the growth stage. At the growth stage, there is an increase in the size of first-order spermatocytes by about 4 times. The maturation stage includes the meiotic division of first-order spermatocytes with the formation, first, from the 1st cell of two second-order spermatocytes, and then 4 spermatids containing a haploid set of chromosomes - 22 autosomes each plus an X or Y chromosome. The spermatid is 4 times smaller than the first-order spermatocyte. After formation, they are located near the lumen of the tubule. The last stage of spermatogenesis is the formation stage. It is absent in ovogenesis. At this stage, the morphological differentiation of spermatids and the formation of spermatozoa occur. At this stage, the spermatozoa acquire their final form - a tail is formed, energy reserves. The nucleus compaction occurs, the centrioles migrate to one of the poles of the nucleus, organizing the axoneme. Mitochondria are arranged spirally, forming a sheath around the axoneme. The Golgi complex develops into an acrosome. The process of spermatogenesis from spermatogonia to the formation of a mature spermatozoon lasts about 65 days, but the final differentiation of spermatozoa occurs in the duct of the epididymis for another 2 weeks. Only after this, the spermatozoa become completely mature and acquire the ability to move independently in the female genital tract. At the stages of reproduction, growth and maturation, spermatogenic cells form cell associations. For example, light type A spermatogonia form a syncytium in which cells are linked by cytoplasmic bridges prior to the formation stage. The cell association in its development from the stage of spermatogonia to the spermatozoon passes through six stages, each of which is characterized by a certain combination of spermatogenic cells. Ovogenesis Unlike spermatogenesis, oogenesis includes three stages - the stages of reproduction, growth and maturation. The reproduction stage occurs in the female body during intrauterine development. By the 7th month of embryogenesis, oogonia stop dividing. At this time, in the ovaries of a female fetus there are up to 10 million first-order oocytes. After completion of the growth stage, oocytes of the first order in the prophase of the first division of meiosis acquire a membrane of follicular cells, after which they fall into a long state of rest, ending in the period of sexual development. The ovaries of a newborn girl contain about 2 million first-order oocytes. The maturation stage occurs during puberty, after the establishment of the ovarian-menstrual cycle. At the level of luteinizing hormone, the first division of meiosis is completed, after which the first-order oocyte enters the fallopian tube. The second meiotic division occurs only under the condition of fertilization, with the formation of one second-order oocyte and a polar (or directional) body. A mature egg contains a haploid set of chromosomes - 22 autosomes and one X chromosome. Male reproductive system The male reproductive system includes the sex glands - testicles, a collection of ducts (efferent tubules, epididymal duct, vas deferens, ejaculatory duct), accessory sex glands (seminal vesicles, prostate and bulbourethral glands) and the penis. Unlike the ovaries, which are located in the small pelvis (in the abdominal cavity), the testicles are located outside the body cavities - in the scrotum. This arrangement can be explained by the need for a certain temperature (not higher than 34 ° C) for the normal course of spermatogenesis. Outside, the testicle is covered with a connective tissue plate or tunica albuginea. The inner layer of the membrane, rich in blood vessels, forms the choroid. The albuginea forms a thickening, which on one side protrudes into the parenchyma of the testis, thereby forming the testicular mediastinum (or Gaimar's body). From the Gaimar body, the albuginea passes into the testicle, piercing the partitions that divide the parenchyma into conical lobules. Each lobule contains from one to four convoluted seminiferous tubules lined with spermatogenic epithelium. Convoluted seminiferous tubules perform the main function of the testicle - spermatogenesis. Loose connective tissue is located between the seminiferous tubules. It contains interstitial Leydig cells. Leydig cells can be attributed to the cells of the endocrine system. They synthesize male sex hormones - androgens. Leydig cells are characterized by a highly developed synthetic apparatus - a smooth endoplasmic reticulum, numerous mitochondria and vacuoles. Among the male sex hormones that are synthesized in Leydig cells, testosterone and dihydrotestosterone are isolated. Stimulation of the synthesis of these hormones is carried out under the influence of lutropin, a hormone that has a stimulating effect on interstitial cells. After isolation from Leydig cells, testosterone enters the bloodstream, where it binds to plasma transport proteins, and when it enters the testicular tissue, to androgen-binding protein. The function of the androgen-binding protein is to maintain a high (necessary for spermatogenesis) level of testosterone in the spermatogenic epithelium by transporting testosterone in the lumen of the seminiferous tubules. As they approach the mediastinum of the testis, the convoluted seminiferous tubules become straight. The wall of the straight tubules is lined with cuboidal epithelium located on the basement membrane. The straight tubules form a testicular network - a system of anastomosing tubules, which then continue into the efferent tubules of the epididymis. The structure of the convoluted seminiferous tubules and Sertoli cells. The convoluted seminiferous tubules are internally lined with spermatogenic epithelium, which contains two types of cells - gametes at various stages of development (spermatogonia, first and second order spermatocytes, spermatids and spermatozoa), as well as supporting Sertoli cells. Outside, the convoluted seminiferous tubules are surrounded by a thin connective tissue sheath. Sertoli cells (or supporting cells) are located on the basement membrane, with their wide base located on the membrane, and the apical part facing the lumen of the tubule. Sertoli cells divide the spermatogenic epithelium into basal and adluminal spaces. Only spermatogonia are located in the basal space, and spermatocytes of the first and second orders, spermatids and spermatozoa are located in the adluminal space. Functions of Sertoli cells: 1) secretion of androgen-binding protein, which regulates the level of testosterone in the spermatogenic epithelium of the convoluted seminiferous tubules; 2) trophic function. Sertoli cells provide the developing gametes with nutrients; 3) transport. Sertoli cells provide the secretion of fluid necessary for the transport of a spermatozoa in the seminiferous tubules; 4) phagocytic. Sertoli cells phagocytize the remnants of the cytoplasm of the emerging spermatozoa, absorb various metabolic products and degenerating sex cells; 5) secretion of the SCF factor (stem cell factor), which ensures the survival of spermatogonia. Hormonal regulation of spermatogenesis. In the hypothalamus, gonadoliberins are secreted, which activate the synthesis and secretion of gonadotropic hormones of the pituitary gland. They, in turn, affect the activity of Leydig and Sertoli cells. The testicles produce hormones that regulate the synthesis of releasing factors on the feedback principle. Thus, the secretion of gonadotropic hormones from the pituitary gland is stimulated by GnRH, and inhibited by testicular hormones. Gonadoliberin enters the bloodstream from the axons of neurosecretory cells in a pulsating mode, with peak intervals of about 2 hours. Gonadotropic hormones also enter the bloodstream in a pulsating mode, at intervals of 90-120 minutes. Gonadotropic hormones include lutropin and follitropin. The targets of these hormones are the testicles, and Sertoli cells have receptors for follitropin, and Leydig cells for lutropin. In Sertoli cells, under the influence of follitropin, the synthesis and secretion of androgen-binding protein, inhibin (a substance that inhibits the synthesis of follitropin in its excess), estrogens, and plasminogen activators are activated. Under the influence of lutropin, the synthesis of testosterone and estrogen is stimulated in Leydig cells. Leydig cells synthesize about 80% of all estrogen produced in the male body (the remaining 20% are synthesized by cells of the fascicular and reticular cortex zones of the adrenal cortex and Sertoli cells). The function of estrogens is to suppress the synthesis of testosterone. The structure of the epididymis. The epididymis consists of a head, body, and tail. The head consists of 10 - 12 efferent tubules, the body and tail are represented by the duct of the appendage, into which the vas deferens opens. The efferent tubules of the appendage are lined with garland epithelium - its cells have different heights. There are tall cylindrical cells, equipped with cilia, which facilitate the movement of spermatozoa, and a low cuboidal epithelium, which contains microvilli and lysosomes, whose function is to reabsorb the fluid formed in the testicles. The duct of the body of the appendage is lined with a multi-row cylindrical epithelium, in which two types of cells are distinguished - basal intercalary and high cylindrical. Cylindrical cells are equipped with stereocilia glued together in the form of a cone - the plasma epithelium. Between the bases of cylindrical cells are small intercalated cells, which are their precursors. Under the epithelial layer is a layer of circularly oriented muscle fibers. The muscular layer becomes more pronounced towards the vas deferens. The main role of the muscles is the promotion of spermatozoa into the vas deferens. The structure of the vas deferens. The wall of the vas deferens is quite thick and is represented by three layers - mucous, muscular and adventitious membranes. The mucous membrane consists of its own layer and multilayer epithelium. In the proximal part, it is similar in structure to the epithelium of the duct of the appendage. The muscular layer has three layers - inner longitudinal, middle circular and outer longitudinal. On the value of the muscular membrane - the release of sperm during ejaculation. Outside, the duct is covered with an adventitial membrane, consisting of fibrous connective tissue with blood vessels, nerves, and groups of smooth muscle cells. The structure of the prostate. The development of the prostate gland is carried out under the influence of testosterone. Before puberty, the volume of the gland is insignificant. With the activation of the synthesis of male sex hormones in the body, its active differentiation, growth and maturation begin. The prostate gland consists of 30-50 branched tubular alveolar glands. It is covered on the outside with a connective tissue capsule containing smooth muscle cells. Connective tissue partitions extend from the capsule deep into the gland, dividing the gland into lobules. In addition to the connective tissue, these partitions include well-developed smooth muscles. The mucous membrane of the secretory sections is formed by a single layer of cuboidal or cylindrical epithelium, which depends on the phase of secretion. The excretory ducts of the gland are lined with multi-row prismatic epithelium, which becomes transitional in the distal sections. Each lobule of the gland has its own excretory duct, which opens into the lumen of the urethra. The secretory cells of the prostate produce a fluid that is secreted into the urethra by contraction of smooth muscle. The secret of the gland is involved in the liquefaction of sperm and promotes its movement through the urethra during ejaculation. In the secret of the prostate gland there are lipids that perform a trophic function, enzymes - fibrinolysin, which prevent spermatozoa from sticking together, as well as acid phosphatase. Seminal vesicles are bulbourethral glands. The seminal vesicles are two symmetrical, highly convoluted tubes, up to 15 cm long. They open into the ejaculatory duct immediately after the vas deferens. The wall of the seminal vesicles consists of three membranes - internal mucosa, middle muscular and external connective tissue. The mucous membrane is formed by a single layer of multi-row cylindrical epithelium containing secretory and basal cells. It has numerous folds. The muscular coat consists of two layers - the inner circular and the outer longitudinal. The seminal vesicles secrete a yellowish liquid. It consists of fructose, ascorbic and citric acids, prostaglandins. All these substances provide the energy supply of spermatozoa and increase their survival in the female genital tract. The secret of the seminal vesicles is ejected into the ejaculatory duct during ejaculation. The bulbourethral glands (or Cooper's glands) have a tubular-alveolar structure. The mucous membrane of the secretory cells of the glands is lined with cubic and cylindrical epithelium. The value of glandular secretions is to lubricate the urethra before ejaculation. The secret is released during sexual arousal and prepares the urethral mucosa for the movement of sperm. The structure of the male penis. The male penis consists of three cavernous bodies. The cavernous bodies are paired and cylindrical and are located on the dorsal side of the organ. On the ventral side along the midline is the spongy body of the urethra, which forms the glans penis at the distal end. Cavernous bodies are formed by an anastomosing network of septa (trabeculae) of connective tissue and smooth muscle cells. Capillaries open into the free spaces between the endothelium-covered septa. The head of the penis is formed by dense fibrous connective tissue containing a network of large tortuous veins. The cavernous bodies are surrounded on the outside by a dense connective tissue protein membrane, consisting of two layers of collagen fibers - the inner circular and the outer longitudinal. There is no albuginea on the head. The head is covered with thin skin, in which there are many sebaceous glands. The cavernous bodies are united by the fascia of the penis. The foreskin is called a circular fold of skin covering the head. In a relaxed state, the large arteries of the penis, which pass in the septa of the cavernous bodies, are spirally twisted. These arteries are muscular type vessels, as they have a thick muscular membrane. A longitudinal thickening of the inner membrane, consisting of bundles of smooth muscle cells and collagen fibers, bulges into the lumen of the vessel and serves as a valve that closes the lumen of the vessel. A significant proportion of these arteries open directly into the intertrabecular space. The veins of the penis have numerous smooth muscle elements. In the middle shell there is a circular layer of smooth muscle fibers, in the inner and outer shells there are longitudinal layers of smooth muscle tissue. During an erection, the smooth muscle tissue of the septa and spiral arteries relax. Due to the relaxation of smooth muscle tissue, blood enters the free spaces of the corpora cavernosa almost without resistance. Simultaneously with the relaxation of the smooth muscles of the septa and arteries of the spiral type, the smooth muscle cells of the veins contract, as a result of which resistance to the outflow of blood from the intertrabecular spaces overflowing with it develops. Relaxation of the penis (or detumescence) occurs as a result of the reverse process - relaxation of the smooth muscles of the veins and contraction of the muscles of the spiral-type arteries, as a result of which the outflow of blood from the intertrabecular spaces improves and the inflow becomes more difficult. The innervation of the penis is carried out as follows. The skin and choroid plexus of the head, the fibrous membranes of the cavernous bodies, the mucous membrane and muscular membrane of the membranous and prostatic parts of the urethra are strong reflexogenic zones saturated with various receptors. Each of these zones plays its role during sexual intercourse, being a reflexogenic zone that underlies unconditioned reflexes - erection, ejaculation, orgasm. Among the nerve elements in the penis, one can distinguish - free nerve endings, bodies of Vater - Pacini, Meissner, Krause flasks. The structure of the male urethra. The urethra in men is a tube about 12 cm long, passing through the prostate, perforating the fascia of the urogenital diaphragm, penetrating the spongy body of the urethra and opening with the external opening of the urethra on the glans penis. In the male urethra, respectively, there are: 1) the prostatic part; 2) membranous part; 3) spongy part; In the prostatic part, the lumen of the urethra has a v-shape. This shape is due to the v-shaped protrusion of the wall of the crest of the urethra. Along the crest are two sinuses into which the ducts of the main and submucosal glands open. On either side of the ridge, ejaculatory channels open. In the region of the internal opening of the urethra, smooth muscle cells of the outer circular layer are involved in the formation of the sphincter of the bladder. The external sphincter of the bladder is formed by the skeletal muscles of the pelvic diaphragm. If the prostatic part of the urethra was characterized by transitional epithelium, then in the membranous part it is replaced by a multilayer cylindrical epithelium. The mucous and muscular membranes of both the prostatic and membranous parts have a powerful receptor innervation. During ejaculation, strong periodic contractions of smooth muscle cells occur, causing irritation of sensitive endings and orgasm. After passing through the bulbs of the spongy substance of the penis, the urethra expands, forming the bulb of the urethra. An enlargement of the urethra at the head of the penis is called the navicular fossa. Before the scaphoid fossa, the mucous membrane of the urethra was lined with stratified columnar epithelium, and after it it is replaced by a stratified squamous keratinizing one and covers the glans penis. Authors: Selezneva T.D., Mishin A.S., Barsukov V.Yu. << Back: Excretory system >> Forward: Female reproductive system
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