Epiphysis
The unpaired organ, up to 0.2 g, is located above the upper tubercles of the quadrigeminum (diencephalon). It is formed in embryogenesis in the form of a small protrusion of the dorsal wall of the intermediate medullary vesicle. It produces and releases hormones into the blood that regulate all cyclical changes in the body: daily, circadian rhythms. It receives light stimulation from the retina through the sympathetic nerve pathways, the monthly cycles. The epiphysis is covered on the outside with a connective tissue capsule, from which thin connective tissue septa extend, dividing the gland into indistinct lobules. The septa contain hemocapillaries. The stroma of the lobules consists of glial cells, their concentration increases towards the periphery, where they form a marginal veil, and pinealocytes are located in the center. These are neurosecretory cells, they have a large nucleus, well-developed organelles, and the processes of these cells extend into the connective tissue septa and end at the hemocapillaries. These cells produce the neuroamine serotonin. It is produced during the daytime, and at night it is converted into the hormone serotonin. These hormones act on the hypothalamus. Serotonin enhances function, and melatonin weakens it. These hormones inhibit the development of the reproductive system. The pineal gland produces antigonadotropic hormone; a hormone that regulates mineral metabolism; a large number of regulatory peptides (liberins and statins), which exert their effects either through the hypothalamus or directly on the pituitary gland. The pineal gland reaches its maximum development at the age of 5-7 years, then it atrophies and its mineralization occurs (Ca salts are deposited).
Reproductive system.
Functions: hormonal, reproductive.
(It occurs simultaneously with the development of the urinary system. On the basis of the primary kidney (lasts 40 hours), the reproductive gonad begins to form. Along its edge, a thickening is formed in the form of a fold of coelomic epithelium, from which the genital ridge is formed. Epithelial cords are formed from the epithelium of this ridge. Sex cells ( gametoblasts) are localized outside this primordium. In most mammals and humans, gametoblasts are formed in the wall of the yolk sac (in the wall of the mesentery of the intestine). Later, these cells begin to migrate into the epithelial cords of the genital ridges. This migration is easy to trace, since gametoblasts are richer in phosphatase and have more large size compared to other cells. There are 2 ways of migration of gametoblasts - through the mesenchyme and through blood vessels. Migration through the vessels leads to the fact that gametoblasts are carried to other areas and tumors can form.
With further development, connective tissue grows between the urinary tubules and the genital ridge, which leads to a reduction of the primary kidney. On their territory, epithelial cords grow from the genital ridges, which contain primary germ cells-gonocytes. The existing mesonephric duct flows into the primary gut and, under the influence of special hormones, it undergoes splitting into the mesonephric and paramesonephric ducts. This state is called indifferent.
At 5-6 weeks, differentiation according to the male type occurs. In the primordium, first-level inhibins are produced, which regulate the reduction of the paramesonephric duct, and in girls it’s the other way around. Therefore, in the future, the fetus will have a formation in the proximal part from the female duct - the prostatic uterus. They form dense formations that are located in the area of the head of the appendage and sometimes require surgical intervention.
Differentiation into the female type occurs at 6-8 weeks, when the unnecessary part of the male type is reduced.
In the first weeks of pregnancy (4-5), caution is required in the use of steroid-type hormonal drugs.)
By week 6, a primary kidney is present. Mesonephric duct and paramesonephric duct. This is the indifferent stage.
During development according to the male type - differentiated stage - the sex cords grow towards the primary bud, gonoblasts and epithelial cells proliferate. Convoluted seminiferous tubules are formed from the sex cords. In this case, spermatogenic epithelium is formed from the gonobalsts, which forms spermatozoa. And from epithelial cells - supporting cells. Straight convoluted tubules and tubules of the testicular network are formed from the cords. The efferent tubules are formed from the tubules of the primary kidney. At 8-10 weeks of embryogenesis, testosterone begins to be produced in the testicle. When the testicle is laid (6-7 weeks), the hormone inhibin begins to be produced, which causes the paramesonephric duct to rupture, leaving only its lower section, from which the male uterus develops. The mesonephric duct gives rise to the vas deferens—the epididymal duct, the ejaculatory duct, and the ejaculatory duct.
If there is not enough inhibin, then the paramesonephric duct develops and the male and female reproductive tracts are simultaneously formed. Hermphroditicism develops.
Male reproductive system.
Testicle- male reproductive gland. The outside is covered with a dense connective tissue tunica albuginea (formed connective tissue), which has a thickening called the mediastinum on the rear inner surface. Connective tissue septa extend from the mediastinum to the convex part of the tunica albuginea, which divide the gland into lobules (100-250). The lobules contain convoluted and straight seminiferous tubules. In terms of length, convoluted ones predominate (up to 70 cm), there are from 1 to 4 of them in a lobe (on average 500-1000). Between the bends of the convoluted tubule there are thin layers of loose connective tissue that contain blood capillaries and interstitial cells(glandulocytes), located in groups, are large, round-shaped cells with well-developed organelles. These are endocrine cells that produce male hormones androgens. Mainly testosterone (of lipid nature). The activity of these cells is stimulated by luteinizing hormone from the pituitary gland. The convoluted seminiferous tubule is externally limited by the basement membrane. The wall of this tubule contains supporting cells and spermatogenic epithelium.
Supporting cells(suspentocytes) - large cells with a wide spread base, a long thin body and an apex facing the lumen of the tubule, contains a large spherical nucleus, well-developed organelles and the cell membrane forms recesses-pockets for developing sperm, ensuring trophism of the spermatogenic epithelium, phagocytosis of destroyed cells, toxic substances that accumulate testosterone on their surfaces; they themselves stimulate the formation of testosterone (that is, they create conditions for spermatogenesis). Between these cells are cells spermatogenic epithelium, spermatogenesis (formation of sperm) occurs in it. There are 4 periods of spermatogenesis: reproduction, growth, maturation, formation. The basis of spermatogenesis is the proliferation and differentiation of spermatogenic epithelial cells. As they differentiate, these cells move from outside to inside (towards the lumen of the seminiferous tubule).
Closer to the basement membrane are spermatogonia - small, round-shaped cells, some of them are in a state of rest - stem cells, they are the most resistant to the action of damaging factors. The other part of the spermatogonia proliferates. This amounts to breeding season. Part of the proliferating cells moves into the inner part, moves away from the membrane and enters growth period. They turn into first-order spermatocytes. These are the largest round cells. The main changes during the growth period occur in the chromosomal apparatus. There are 4 phases here:
· Leptotene - chromosomes unwind, they become long and thin.
· Zygotene - homologous chromosomes are located parallel to each other, and homologous regions are exchanged.
· Pachytene - the reverse process of chromosomes twisting, they become short and thick.
· Diplotene - splitting of chromosomes, from 2 chromosomes 4 chromatids are formed.
Maturation period-it is based on reduction division (meiosis). After the first division, 2 spermatocytes of the 2nd order with a diploid set of chromosomes are formed. Spermatocytes of the 2nd order are round in shape, small, displaced inward. Division 2 occurs immediately. From each 2nd order sprematocyte, 2 chromatids with a haploid set of chromosomes are formed. They are externally similar to 2nd order spermatocytes, they move inward and towards the supporting cells, and are immersed in the pockets of the cytolemma (closer to nutrients). Due to the supporting cells, trophism is enhanced, the cells become oval, and a period of formation begins. Part of the cytoplasm is shed, the head, neck, and tail are formed (spermatozoa are formed), the tail section faces the lumen of the convoluted tubule.
The duration of spermatogenesis is 2.5 months, continuous. From one spermatocyte of the 1st order, 4 spermatozoa are formed. Spermatogonia are the most resistant and, as cells differentiate, their sensitivity to the action of damaging factors increases. Spermatogenesis in the convoluted tubule proceeds in waves, that is, different cells of the spermatogenic epithelium predominate in different parts of the tubule.
Sperm are separated from the supporting cells into the lumen of the convoluted tubule, the mucous secretion of the supporting cells is released here, sperm is formed in the lumen, then the sperm moves along the convoluted tubules and enters the straight tubules - they are very short, and the spermatic ducts begin with them. Their wall has 3 membranes: mucous, muscular, adventitial.
In straight tubules there is mainly mucosa, which is lined with epithelium. The epithelium of all vas deferens has secretory ability. It produces and secretes slightly alkaline mucus into the lumen. In the tubules of the testicular network (in the mediastinum) the epithelium is flat or cubic, but its activity is low. From this network comes 10-12 efferent tubules; together they form the head of the epididymis. 3 shells are visible. The mucosal epithelium contains tall ciliated cells, and between them secretory cubic cells that secrete mucus. The efferent tubules empty into epididymal duct , form the body and tail of the appendage, and its mucous membrane is lined with double-row ciliated epithelium, which contains small intercalary cells and tall cells with cilia fixed at the apex. Mucus is intensively produced. The epididymal duct is a reservoir for sperm. They mature here, around each sperm there is a thin carbohydrate membrane (glycocalyx). Vas deferens has 3 shells:
The mucous membrane forms 3-4 small longitudinal folds
· Muscular - very wide, powerful. Contains inner and outer longitudinal layers and a pronounced middle circular layer.
· The outer shell is adventitial.
Blood-testis barrier separates the spermatogenic epithelium from the blood of the blood vessels. If immune competent cells enter the spermatogenic epithelium, it is destroyed. The barrier includes:
supporting cells
basement membrane of the convoluted tubule wall,
· connective tissue layer,
· a layer of lipoid cells that contain modified smooth muscle cells and are externally limited by thin basement membranes,
layer of loose connective tissue,
· hemocapillary wall.
The testicle produces prostaglandin, a smaller part of which is released into the blood, and a larger part into the sperm.
Accessory glands: seminal vesicles, bulbourethral glands, prostate gland.
Male and female internal genital organs, although significantly different in structure, nevertheless have common rudiments. In the initial stage of development, there are common cells that are sources of formation of the gonads, associated with the urinary and reproductive ducts (mesonephros duct) (Fig. 341). During the period of differentiation of the gonads, only one pair of ducts reaches development. During the formation of a male individual, convoluted and straight testicular tubules, the vas deferens, and seminal vesicles develop from the genital duct, and the urinary duct is reduced and only the male uterus remains in the colliculus seminalis as a rudimentary formation. When a female is formed, development reaches the urinary duct, which is the source of the formation of the fallopian tube, uterus and vagina, and the genital duct, in turn, is reduced, also giving a rudiment in the form of epoophoron and paroophoron.
341. Schematic representation of the developing male genitourinary system (according to Hertig).
1 - diaphragmatic ligament; 2 - epididymis; 3 - testicle before descending into the scrotum; 4 - bladder; 5 - openings of the ureters; 6 - sinus prostaticus; 7 - prostate gland; 8 - urethra; 9 - scrotum; 10 - testicle after descent; 11 - opening of the ejaculatory duct; 12 - inguinal ligament; 13 - duct of the middle kidney; 14 - mesonephric duct; 15 - ureter; 16 - final bud.
Testicular development. The formation of the testicle is associated with the ducts of the genitourinary system. At the level of the middle kidney (mesonephros), under the mesothelium of the body, the rudiments of the testicle are formed in the form of cords of the testis, which are a derivative of the endodermal cells of the yolk sac. The gonadal cells of the testis cords develop around the ducts of the mesonephros (genital duct). At the fourth month of intrauterine development, the seminal cord disappears and the testicle is formed. In this testicle, each mesonephros tubule is divided into 3-4 daughter tubules, which turn into convoluted tubules that form the testicular lobules. The convoluted tubules join together to form a thin, straight tubule. Between the convoluted tubules, strands of connective tissue penetrate, forming the interstitial tissue of the testicle. The enlarging testicle pushes back the parietal peritoneum; as a result, a fold is formed above the testicle (diaphragmatic ligament) and a lower fold (inguinal ligament of the genital duct). The lower fold turns into a conductor of the testis (gubernaculum testis) and takes part in the descent of the testicle. In the groin area, at the site of attachment of the gubernaculum testis, a protrusion of the peritoneum (processus vaginalis) is formed, merging with the structures of the anterior abdominal wall (Fig. 342). In the future, this protrusion will participate in the formation of the scrotum. After the formation of a protrusion of the peritoneum, the anterior wall of the recess closes into the internal inguinal ring. During the 7th - 8th months of intrauterine development, the testicle passes through the inguinal canal and by the time of birth it finds itself in the scrotum lying behind the peritoneal outgrowth, to which the testicle grows from its outer surface. When moving a testicle from the abdominal cavity to the scrotum or an ovary to the pelvis, it is not entirely correct to talk about its true descent. In this case, it is not subsidence that occurs, but a growth discrepancy. The ligaments located above and below the gonads lag behind the growth rate of the trunk and pelvis and remain in place. As a result, the pelvis and torso increase, and the ligaments and glands “descend” towards the developing torso.
342. The process of lowering the testicle into the scrotum.
1 - peritoneum; 2 - vas deferens; 3 - testicle; 4 - inguinal ligament; 5 - scrotum; 6 - processus vaginalis.
Developmental anomalies. A common developmental anomaly is a congenital inguinal hernia, when the inguinal canal is so wide that the internal organs exit through it into the scrotum. Along with this, there is retention of the testicle in the abdominal cavity near the internal opening of the inguinal canal (cryptorchidism).
Ovarian development. In the area of the seminiferous cord in the female, the germ cells are scattered in the mesenchymal stroma. The connective tissue base and membrane develop poorly. In the mesenchyme of the ovary, the cortical and medullary zones are differentiated. In the cortical zone, follicles are formed, which in a newborn girl, under the influence of the mother’s hormones, increase, and then atrophy after birth. Vessels grow into the medulla. In the embryonic period, the ovary is located above the entrance to the pelvis. With the enlargement of the ovary in the fourth month of development, the inguinal ligament mesonephros bends and turns into the suspensory ligament of the ovary. From its lower end, the ligament of the ovary and the round ligament of the uterus are formed. The ovary will be located between two ligaments in the pelvis (Fig. 343).
343. Schematic representation of the developing female genital organs (according to Hertig).
1 - diaphragmatic ligament of the middle kidney;
2 - opening of the fallopian tube;
3 - ovary;
4 - inguinal ligament;
5 - bladder;
6 - openings of the ureters;
7- urethra;
8 - labia minora;
9 - labia majora;
10 - vagina;
11 - round ligament of the uterus;
12 - round ligament of the ovary (part of the inguinal ligament);
13 - ovary;
14 - fallopian tube after descent;
15 - duct of the middle kidney;
16 - ureter;
17 - final bud.
Developmental anomalies. Sometimes an accessory ovary is observed. A more common anomaly is a change in the topography of the ovary: it can be located at the internal opening of the inguinal canal, in the inguinal canal, or in the thickness of the labia majora. In these cases, abnormal development of the external genitalia may also be observed.
Development of the uterus, fallopian tubes and vagina. The epididymis, vas deferens and seminal vesicles develop from the genital duct, in the wall of which a muscular layer is formed.
The fallopian tubes, uterus and vagina are formed by the transformation of the urinary ducts. During the third month of development, this duct between the ovary and the uterus turns into a fallopian tube with an expansion at the upper end. The fallopian tube is also carried into the pelvis by the descending ovary (Fig. 344).
344. Schematic representation of the formation of the uterus, vagina and mesonephric ducts.
A, B, C: 1 - mesonephric duct; 2 - duct of the middle kidney; 3 - urogenital sinus. G: 1 - fallopian tube; 2 - body of the uterus; 3 - cervix; 4 - vagina; 5 - urogenital sinus.
The urinary ducts in the lower part are surrounded by mesenchymal cells and form an unpaired tube, which is divided by a roller in the second month. The upper part becomes overgrown with mesenchymal cells, thickens and forms the uterus, and the vagina develops from the lower part.
Topic 25. GENITAL SYSTEM
Development of genital organs
The sources of development of the genital organs are the genital ridges and primary germ cells.
The genital (or gonadal) ridges are indifferent gonads, the rudiments of future genital future organs (both male and female) - testes and ovaries.
The genital ridges are formed already in the 4th week of intrauterine development, but at this time it is impossible to identify whether these are male or female. After initiation, the indifferent gonads are populated by primary germ cells of the cortex and medulla.
Primary germ cells are formed in the wall of the yolk sac, after which they migrate to the reproductive gonads. After migration and sexual differentiation, primordial germ cells, under the influence of certain factors, transform into spermatogonia in the testes and into oogonia in the ovaries. However, for final differentiation into sperm and eggs, sex 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 - 50 days (8 weeks) is a critical period of embryo development; it is at this period that sexual differentiation occurs.
During fertilization, chromosomal determination occurs, with the Y chromosome ensuring the subsequent genetic development of the male sex. 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, testes develop from the primary gonads, and the development of further reproductive structures is ensured by male sex hormones and Müllerian inhibitory factor, also produced in the testes.
Indifferent gonads consist of a 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 brain substance develops. At the 8th week of embryogenesis, the testicles are located at the level of the upper lumbar vertebrae, and from their lower pole stretches a suspensory ligament, 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 genitalia are differentiated 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.
The testicles of boys contain Sertoli cells that synthesize 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 Müllerian inhibitory factor, regardless of whether female sex (ovarian) hormones are present or not. In the male body, under the influence of Müllerian inhibitory factor, the paramesonephric ducts undergo degeneration.
Differentiation of the external genitalia is carried out from the urogenital sinus, genital tubercle, genital folds and genital ridges. The development of the external genitalia 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 in the 12th - 14th week of intrauterine development.
The development of the external genitalia according to the female type occurs in the absence of male sex hormones (androgens). The urogenital sinus gives rise to the lower part of the vagina, the genital tubercle becomes the clitoris, and the genital ridges and genital folds become the labia majora and minora.
Gametogenesis
Spermatogenesis
The process of formation of male reproductive cells goes through four stages - reproduction, growth, maturation and formation.
Reproduction and growth stage. After formation, primary germ cells migrate to the gonad primordia, where they divide and differentiate into spermatogonia. In the spermatogonia stage, the sex cells remain dormant until the period of sexual reproduction. Under the influence of male sex hormones and primarily testosterone, spermatogonia begin to multiply. 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, affecting the secretion of Leydig cells. At the reproductive stage, 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 light cells can proceed symmetrically (in which two type B spermatogonia are formed) or asymmetrically, in which one type B spermatogonia and one type A light cell are formed.
Type B spermatogonia have a round nucleus and condensed chromatin. They enter mitosis, but remain connected to each other through cytoplasmic bridges. After undergoing 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, the size of first-order spermatocytes increases approximately 4 times.
The maturation stage includes the meiotic division of first-order spermatocytes with the formation, first from 1 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 size of a spermatid is 4 times smaller than a 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 oogenesis. At this stage, morphological differentiation of spermatids and the formation of spermatozoa occurs. At this stage, sperm acquire their final form - a tail and energy reserves are formed. The nucleus becomes compacted, the centrioles migrate to one of the poles of the nucleus, organizing an axoneme. Mitochondria are arranged in a spiral, forming a shell around the axoneme. The Golgi complex turns into an acrosome.
The process of spermatogenesis from spermatogonia to the formation of a mature sperm lasts about 65 days, but the final differentiation of sperm occurs in the epididymal duct within another 2 weeks.
Only after this do sperm become fully mature and acquire the ability to move independently in the female genital tract.
During the stages of reproduction, growth and maturation, spermatogenic cells form cellular associations. For example, light type A spermatogonia form a syncytium in which the cells are connected by cytoplasmic bridges before the formation stage. The cell association in its development from the stage of spermatogonia to the sperm goes through six stages, each of which is characterized by a certain combination of spermatogenic cells.
Oogenesis
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 completing the growth stage, first-order oocytes in the prophase of the first division of meiosis acquire a shell of follicular cells, after which they enter a long-term state of rest, ending during sexual development.
The ovaries of a newborn girl contain about 2 million first-order oocytes.
The maturation stage begins during puberty, after the establishment of the ovarian-menstrual cycle. At the height of luteinizing hormone, the first meiotic division is completed, after which the first-order oocyte exits into the fallopian tube. The second meiotic division occurs only upon fertilization, producing 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 - the testes, a set of ducts (the efferent tubules, the epididymal duct, the vas deferens, the ejaculatory duct), the accessory sex glands (the seminal vesicles, the prostate gland and the bulbourethral glands) and the penis.
Unlike the ovaries, which are located in the 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.
On the 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 tunica albuginea forms a thickening, which on one side protrudes into the testicular parenchyma, thereby forming the mediastinum of the testicle (or maxillary body). The tunica albuginea passes from the maxillary body into the testicle, piercing the septa 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.
Between the seminiferous tubules there is loose connective tissue. It contains interstitial Leydig cells. Leydig cells can be classified as 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 are testosterone and dihydrotestosterone. 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 being released from Leydig cells, testosterone enters the blood, where it binds to plasma transport proteins, and when it enters testicular tissue, to androgen-binding protein.
The function of androgen binding protein is to maintain high (necessary for spermatogenesis) testosterone levels in the spermatogenic epithelium by transporting testosterone in the lumen of the seminiferous tubules.
As they approach the mediastinum of the testicle, the convoluted seminiferous tubules turn into straight ones. The wall of the straight tubules is lined with cuboidal epithelium located on the basement membrane. Straight tubules form the rete testis - a system of anastomosing tubules, which then continue into the efferent tubules of the epididymis.
The structure of convoluted seminiferous tubules and Sertoli cells. The convoluted seminiferous tubules are lined from the inside by spermatogenic epithelium, which contains two types of cells - gametes at different stages of development (spermatogonia, first- and second-order spermatocytes, spermatids and spermatozoa), as well as supporting Sertoli cells.
On the outside, the convoluted seminiferous tubules are surrounded by a thin connective tissue membrane.
Sertoli cells (or supporting cells) are located on the basement membrane, with their wide base located on the membrane, and their apical part facing the lumen of the tubule. Sertoli cells divide the spermatogenic epithelium into the basal and adluminal spaces.
The basal space contains only spermatogonia, and the adluminal space contains first- and second-order spermatocytes, spermatids and spermatozoa.
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 nutrients to developing gametes;
3) transport. Sertoli cells provide the secretion of fluid necessary for the transport of sperm in the seminiferous tubules;
4) phagocytic. Sertoli cells phagocytose the remains of the cytoplasm of developing spermatozoa, absorb various metabolic products and degenerating germ cells;
5) secretion of SCF factor (stem cell factor), which ensures the survival of spermatogonia.
Hormonal regulation of spermatogenesis. The hypothalamus secretes gonadoliberins, which activate the synthesis and secretion of gonadotropic hormones of the pituitary gland. They, in turn, influence the activity of Leydig and Sertoli cells. The testes produce hormones that regulate the synthesis of releasing factors using a feedback principle. Thus, the secretion of gonadotropic hormones of the pituitary gland is stimulated by GnRH and inhibited by testicular hormones.
Gonadotropin-releasing hormone 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, with 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 when it is in excess), estrogens, and plasminogen activators is activated.
Under the influence of lutropin, the synthesis of testosterone and estrogens is stimulated in Leydig cells. Leydig cells synthesize about 80% of all estrogens produced in the male body (the remaining 20% are synthesized by cells of the zona fasciculata and reticularis of the adrenal cortex and Sertoli cells). The function of estrogen is to suppress testosterone synthesis.
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 epididymal duct, into which the vas deferens opens.
The efferent tubules of the epididymis are lined with garland epithelium - its cells have different heights. There are tall cylindrical cells equipped with cilia, which facilitate the movement of sperm, and 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 epididymis is lined with multirow 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 - plasma epithelium. Between the bases of the cylindrical cells there are small intercalary cells, which are their predecessors. Under the epithelial layer there is a layer of circularly oriented muscle fibers. The muscle layer becomes more pronounced towards the vas deferens.
The main role of the muscles is to propel sperm into the vas deferens.
Structure of the vas deferens. The wall of the vas deferens is quite thick and is represented by three layers - mucous, muscular and adventitial membranes.
The mucous membrane consists of its own layer and multirow epithelium. In the proximal part, it is identical in structure to the epithelium of the epididymal duct. The muscular layer has three layers - the inner longitudinal, middle circular and outer longitudinal. The meaning of the muscular membrane is the release of sperm during ejaculation. The outside of the duct is covered with an adventitial membrane, consisting of fibrous connective tissue with blood vessels, nerves and groups of smooth muscle cells.
Structure of the prostate gland. 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 begins.
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 septa extend from the capsule deep into the gland, dividing the gland into lobules. In addition to connective tissue, these septa contain well-developed smooth muscles.
The mucous membrane of the secretory sections is formed by single-layer cubic or columnar epithelium, which depends on the phase of secretion.
The excretory ducts of the gland are lined with multirow 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 gland produce fluid, which, due to the contraction of smooth muscle muscles, is released into the urethra. The secretion of the gland takes part in the liquefaction of sperm and promotes its movement through the urethra during ejaculation.
The secretion of the prostate gland contains lipids that perform a trophic function, enzymes - fibrinolysin, which prevent sperm from sticking together, as well as acid phosphatase.
Seminal vesicles 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 - the inner mucosa, the middle muscular and the outer connective tissue.
The mucous membrane is formed by a single-layer multirow columnar epithelium containing secretory and basal cells. It has numerous folds.
The muscular layer consists of two layers - the inner circular and outer longitudinal.
The seminal vesicles secrete a yellowish liquid. It contains fructose, ascorbic and citric acids, prostaglandins. All these substances provide energy reserves for sperm and increase their survival in the female genital tract. The secretion of the seminal vesicles is released into the ejaculatory duct during ejaculation.
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 columnar epithelium. The meaning of the secretion of the glands is to lubricate the urethra before ejaculation. The secretion is secreted 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 there is the spongy body of the urethra, which forms the glans penis at the distal end. The corpora cavernosa are formed by an anastomosing network of septa (trabeculae) made of connective tissue and smooth muscle cells. Capillaries open into the free spaces between the endothelium-covered septa.
The glans penis is formed by dense fibrous connective tissue containing a network of large convoluted veins.
The corpora cavernosa are externally surrounded by a dense connective tissue tunica albuginea, consisting of two layers of collagen fibers - the inner circular and the outer longitudinal. There is no tunica albuginea on the head.
The head is covered with thin skin containing many sebaceous glands.
The corpora cavernosa are united by the fascia of the penis.
The foreskin is a circular fold of skin covering the glans.
In a relaxed state, the large arteries of the penis, which pass through the septa of the corpora cavernosa, are spirally twisted. These arteries are muscular type vessels, as they have a thick muscular layer. 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 closing the lumen of the vessel. A significant portion 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 relaxes. Due to the relaxation of smooth muscle tissue, blood flows into the free spaces of the cavernous bodies with virtually no resistance. Simultaneously with the relaxation of the smooth muscles of the septa and spiral arteries, the smooth muscle cells of the veins contract, resulting in the development of resistance to the outflow of blood from the intertrabecular spaces, which are overcrowded with it.
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 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, fibrous membranes of the corpora cavernosa, mucous and muscular membranes of the membranous and prostatic parts of the urethra are strong reflexogenic zones, saturated with a variety of 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, Vater-Pacini, Meissner, and Krause flasks.
The structure of the male urethra. The male urethra is a tube about 12 cm long that passes through the prostate, pierces the fascia of the urogenital diaphragm, penetrates the spongy body of the urethra and opens into the external opening of the urethra at the glans penis.
In the male urethra, accordingly, there are:
1) prostatic part;
2) membranous part;
3) spongy part;
In the prostatic part, the lumen of the urethra is v-shaped. This form is caused by a v-shaped protrusion of the wall of the urethral ridge. Along the ridge there are two sinuses into which the ducts of the main and submucosal glands open. Ejaculatory canals open on both sides of the ridge. In the area of the internal opening of the urethra, smooth muscle cells of the outer circular layer participate in the formation of the bladder sphincter.
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 a transitional epithelium, then in the membranous part it is replaced by a multilayer cylindrical one. The mucous and muscular membranes of both the prostatic and membranous parts have powerful receptor innervation.
During ejaculation, strong periodic contractions of smooth muscle cells occur, causing irritation of the sensitive endings and orgasm.
After passing through the bulbs of the spongy substance of the penis, the urethra expands to form the bulb of the urethra. The dilatation 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 keratinized stratified squamous epithelium and covers the glans penis.
From the book Therapeutic. Folk methods. author Nikolai Ivanovich Maznev From the book Treatment of Male Diseases. Proven Methods author Nikolai Ivanovich MaznevTopic 20. ENDOCRINE SYSTEM The endocrine system, together with the nervous system, has a regulatory effect on all other organs and systems of the body, forcing it to function as a single system. The endocrine system includes glands that do not have excretory
From the book How to stop aging and become younger. Result in 17 days by Mike MorenoTopic 21. DIGESTIVE SYSTEM The human digestive system is a digestive tube with glands located next to it, but outside it (salivary glands, liver and pancreas), the secretion of which is involved in the digestion process. Sometimes
From the book A Healthy Man in Your Home author Elena Yurievna ZigalovaTopic 22. RESPIRATORY SYSTEM The respiratory system includes various organs that perform air-conducting and respiratory (gas exchange) functions: the nasal cavity, nasopharynx, larynx, trachea, extrapulmonary bronchi and lungs. The main function of the respiratory system is
From the author's bookTopic 24. EXCRETORY SYSTEM The excretory system includes the kidneys, ureters, bladder and urethra. Development of the excretory system The urinary and reproductive systems develop from the intermediate mesoderm. At the same time, consistently
From the author's bookTopic 26. FEMALE GENITAL SYSTEM The female reproductive system consists of paired ovaries, uterus, fallopian tubes, vagina, external genitalia and paired mammary glands. The main functions of the female reproductive system and its individual organs: 1) the main function is reproductive; 2)
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From the author's bookAnti-Aging Measures and Your Reproductive System 1. Movement. Whenever my patient complains of erectile dysfunction, I ask him: “Do you exercise?” And as soon as I see that he hesitates to answer, I order: “Start moving!” First,
From the author's bookMale reproductive system The male reproductive system includes the internal and external male genitalia. The internal male genital organs include the testes, epididymis, vas deferens, seminal vesicles, ejaculatory duct, urethra,
From the author's bookFemale reproductive system This book is about a man and for a man. But always, at all times, a woman is a mystery, a woman, her body and soul interest a man, perhaps even more than he himself. And therefore we will talk about the features of the female body, in particular, about the female genital organs.
In the development of the genital organs, there are 2 stages: 1) indifferent anlage, 2) differentiation according to the male or female type
In the human embryo, at the 4-5th week of intrauterine development, indifferent gonads are identified, located on the ventral surface of the mesonephros in the form of a thickened ridge of coelomic epithelium. Sex cords are formed in the gonad, primary germ cells are determined, which penetrate into the anlage with the bloodstream or through the endoderm of the hindgut from the yolk sac. At the 5th week of embryological development, the paramesonephric duct is formed along the lateral edge of the primary kidney and the mesonephric duct.
From the mesonephric ducts excretory ducts of the male genital organs are formed.
Internal ducts develop from the paramesonephric ducts female genital organs.
At the 7-8th week of embryogenesis, differentiation indifferent gonad according to male or female type.
Development of internal male genital organs.
Differentiation of male genital organs occurs under the influence of testosterone, which is produced by interstitial cells (Leydig). They are located in the mesenchyme between the sex cords of the testicle. Interstitial cells begin to function in the 3rd month of embryogenesis. A sign of differentiation of the gonad according to the male type is the beginning of the formation of the tunica albuginea, as well as the reduction of the paramesonephric ducts.
The sex cords turn into convoluted and straight seminiferous tubules, and from the tubules of the middle section of the mesonephros (primary kidney) the rete tubules and efferent tubules of the testicle develop. The cranial tubules of the primary kidney are transformed into the appendix epididymis (appendix epididymidis), and the caudal tubules are transformed into the appendix testis (paradidymis).
In male embryos, the mesonephric ducts turn into epididymal duct, vas deferens. The distal end of the mesonephric duct expands and forms the ampulla of the vas deferens, and from the lateral protrusion of the distal part of the mesonephric duct the seminal vesicles develop, from the final narrowed part - the ejaculatory duct, which opens into the prostatic part of the urethra.
From the cranial region The paramesonephric duct is formed: appendix testis; from fused caudal departments – prostatic uterus (utriculus prostaticus), the remaining sections of this duct are reduced.
The testicular anlage is located high in the retroperitoneal space of the abdominal cavity, and during development it moves in the caudal direction.
Factors influencing the process of testicular descent: gubernaculum testis, hormonal, tunica albuginea (it protects the testicle from mechanical damage), growth of retroperitoneal organs, increase in intra-abdominal pressure, differentiation and growth of the epididymis, development of the testicular artery.
For 3 months intrauterine development, the testicle is located in the iliac fossa, at 6 months. - at the deep inguinal ring, at 7-8 months. – in the inguinal canal, by the time of birth – in the scrotum.
Prostate develops from the epithelium of the developing urethra in the 3rd month of intrauterine life.
Bulbourethral glands - develop from epithelial outgrowths of the spongy part of the urethra.
For the right Müllerian duct differentiation and the urogenital sinus in an adequately developing female embryo requires a series of well-regulated, complexly interrelated events. Despite their origins in different germ layers, the fates of the Müllerian ducts (mesodermal origin) and the urogenital sinus (endodermal origin) are closely intertwined as they differentiate to form the female reproductive tract.
Müllerian ducts- the primary rudiment of the internal female genital organs, as a result of differentiation of which the fallopian tubes, uterus, cervix and upper parts of the vagina are formed. When the dynamic processes of differentiation, migration, fusion and formation of anatomical structures are disrupted, a wide variety of congenital anomalies of the reproductive tract are possible. Anatomical malformations have a wide range: from agenesis of the uterus and vagina to duplication of the genital organs.
Violation local mesoderm development from the corresponding somites can lead to the combined formation of urological and skeletal abnormalities.
Ovaries, like the testes, develop from indifferent gonads, which, in turn, are formed from three different cellular representations: mesothelium, mesenchyme and primordial germ cells (PPC). In the absence of moderator genes on the Y chromosome or the Y chromosome itself, indifferent gonads differentiate into ovaries, starting at approximately the 10th week of embryogenesis. At 16 weeks, primary follicles begin to develop.
Development of the external genitalia begins at the 4th week with the formation of the genital tubercle from proliferating mesenchyme, which, lengthening, forms an embryonic indifferent phallus. Urogenital folds differentiate to form the labia minora.
TO 6th week of development both male and female already have paired reproductive ducts: paramesonephric (Müllerian) and mesonephric (Wolffian). Here we use synonymous terms that are used in relation to these ducts in different ways. Thus, most books on embryology use the term “paramesonephric duct,” while clinicians prefer “Müllerian.”
First are formed mesonephric ducts Therefore, within a short period of time, it is they who carry out the excretion of the contents of the primary kidney (mesonephros, Wolffian body) into the cloaca. The key gene responsible for the development of paramesonephric and mesonephric ducts is PAX2. Its mutations lead to impaired development of ducts and kidneys in both sexes.
In a female fetus mesonephric ducts degenerate in the absence of testosterone, and paramesonephric develop due to the absence of anti-Mullerian hormone (AMH). At the same time, the paramesonephric ducts are formed by longitudinal invagination of the coelomic epithelium along the outer wall of the mesonephric ducts. When folding, the coelomic epithelium first forms cords along the entire Wolffian duct from the level of the anterior kidney to the cloaca.
And only when the secretion accumulates, the cords turn into paramesonephric ducts. The reducing mesonephric ducts become an ideal matrix for the elongating paramesonephric ducts. This primary connection explains the subsequent combinations of paramesonephric duct anomalies and urinary tract malformations. In a male fetus, the paramesonephric ducts are not fully transformed into the uterus under the influence of AMH secreted by the Sertoli cells of the testicles. When the gene encoding AMH or its receptors is mutated, male fetuses develop full-fledged Müllerian ducts and a uterus.
As it forms paramesonephric ducts by the 9th week, three of their regions can be distinguished: cranial, horizontal and caudal. Each of them has its own direction of development. The cranial regions, merging with the tubules of the anterior kidney, open directly into the primary cavity of the peritoneum, subsequently forming the fimbriae of the fallopian tubes. The paramesonephric ducts at this level are located lateral to the mesonephric ducts.
Paired horizontal segments move laterally along in relation to the mesonephric ducts, after which they pass ventrally and, extending caudomedially, form the rest of the fallopian tubes. The caudal regions converge with their contralateral counterpart in the midplane in the future pelvic cavity and fuse to form a single Y-shaped structure known as the uterovaginal canal. It consists of the uterine and vaginal sections. The uterine section gives rise to the uterus, the vaginal section gives rise to the upper part of the vagina.
In this stage of development of the uterus has a bicornuate shape, but changes in its structure continue during the process of fusion and subsequent formation of the canal lumen. Canalization or reduction of the uterine septum is mediated by the process of apoptosis, which is regulated by the bd-2 gene. It is believed that fusion occurs in the direction from the caudal to the cranial region. However, the presence of such postnatally detected developmental anomalies as duplication of the cervix and vagina in the normal structure of the uterus suggests the possibility of fusion beginning at the level of the internal isthmus of the uterus with its subsequent spread in both directions.
By the 12th week, the fundus of the uterus takes on the shape characteristic of a mature organ. Endometrium originates from the lining of the fused paramesonephric (Müllerian) ducts, and the endometrial stroma and myometrium are derivatives of the adjacent mesenchyme. The entire process is completed by the 22nd week of development, leading to the formation of a uterus with a single uterine cavity and cervix.
External genitalia of a male and female fetus identical at the indifferent stage of development from the 4th to the 7th week. Characteristic sexual characteristics begin to appear at the 9th week, complete differentiation is completed by the 12th. The mesenchyme of the cranial parts of the cloacal membrane proliferates, forming the genital tubercle. It lengthens, forming the phallus, which later transforms into the clitoris. Genital folds and labioscrotal ridges develop laterally along the cloacal membrane.
By the end of the 6th week urorectal septum descends to the cloacal membrane, dividing it into the anal (dorsal) and urogenital (ventral) parts. The urogenital membrane is located at the bottom of the urogenital groove and is limited by the genital folds. After about a week, the membranes rupture, forming the anal and urogenital openings, respectively.
Sexual folds posteriorly connect, merge and form the frenulum of the labia minora. Their unfused anterior sections become the labia minora. The labial-scrotal folds also merge in the posterior regions, forming the posterior commissure of the labia. When they merge in the anterior sections, the anterior commissure of the labia and the pubic eminence are formed. However, most of the labioscrotal folds remain unfused and form the labia majora.
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