Male reproductive system
Male reproductive glands
The testicles, or testes (testes), are the male gonads in which the male sex cells are formed — the sperm cells and the male sex hormone — testosterone.
The development of the male and female gonad begins in the same type (the so-called indifferent stage) and is closely connected with the development of the excretory system.
There are three components of the developing gonads:
- gonocytes, giving rise to ovogony or spermatogonia;
- derivatives of the mesodermal coelomic epithelium - the future epithelial elements of the gonads;
- mesenchymal tissue - connective tissue and smooth muscle elements of the gonads.
On the medial side of the primary kidney (mesonephros), ridge-shaped thickenings are formed — genital ridges or future gonads. The coelomic epithelium gives rise to genital cords, which grows into the genitals. Subsequently, the sexual cords develop into the seminiferous tubules (tubuli seminiferi), but some of these cords are transformed into the testicular network (rete testis).
In the postnatal period, gonocytes proliferate in the seminiferous tubules, and the epithelium of the genital cords is preserved as supporting cells. In the same genital cords, from which the testicular network develops, the gonocytes are gradually reduced.
The canaliculi of the testicular network, approaching the mediastinal membrane, coalesce into the outgoing tubules (ductuli efferentes), which are formed by restructuring the epithelial lining of the primary kidney. The evacuating testicular tubules, going, pass further into the canal of the epididymis (ductus epididymis), the proximal part of which, writhing repeatedly, forms the epididymis (epididymis), while its distal part becomes the defective duct (ductus defferes).
Male genital tract abnormalities develop from the mesonephral ducts, or the Wolf channels.
Paramesonephral (Mullerian) duct in the male body atrophies and retains only the upper end and the lower end, which turns into a prostatic (male) uterus (utriculus prostaticus), located in an adult male in the thickness of the prostate gland at the confluence of the VAS. The prostate gland and seminal vesicles develop as outgrowths of the urogenital sinus. After the 22nd week, gonocytes turn into spermatogonia, and they lose glycogen and high alkaline phosphatase activity.
In ontogenesis, the endocrine function of the testicle is established earlier than the generative function. The male sex hormone, testosterone, begins to produce GPD at the human embryo, a gene for sexual determination, from about the 8th to 10th week of the prenatal period. In the germ testis, even before the onset of testosterone biosynthesis, several protein (peptide) androgens belonging to inhibins are alternately formed. The hormone appears first at the stage of the indifferent gonad, under the influence of which the paramesonephral duct is reduced, and from this moment the indifferent primordia of the reproductive system is differentiated according to the male type.
By the middle of embryogenesis, when the epithelio-spermatogenous layer already differentiates in the seminiferous testicular tubules, and gonocytes accumulate in large numbers, the production of the second inhibin begins, which, on the one hand, inhibits gonocyte reproduction and causes their destruction, and on the other, simultaneously inhibits secretion FSH adenohypophysis. This peptide is produced by the epithelium of the testicular network.
Finally, as we approach the prenatal period of embryogenesis, the male fetus appears inhibin, which, while retaining the ability to selectively inhibit the secretion of FSH, acts on the corresponding hypothalamic centers.
Outside, most of the testis is covered with a serous membrane - the peritoneum, under which there is a dense connective tissue tunica (tunica albuginea). At the posterior margin of the testicle, it thickens, forming the mediastinum (mediastinum testis), from which connective tissue partitions (septula testis) extend into the gland, dividing the gland into lobules (about 250 lobes). Each lobule contains from 1 to 4 convoluted seminiferous tubules (tubuli seminiferi convoluti). Each seed tubule has a diameter of 150 to 250 microns and a length of 30 to 70 cm. Approaching the mediastinum, the canaliculi (300–450 in each testis) merge and become straight, and in the middle of the mediastinum are connected to the canaliculi of the testicular network. Out of this network (about 10) are the outgoing (efferent) tubules (ductuli efferens), which flow into the duct of the appendage (ductus epididymis).
The inner lining of the seminiferous tubules forms the epithelio-spermatogenic layer (or the so-called spermatogenic epithelium) located on the basement membrane.
Outwardly from the epithelio-spermatogenic layer of the seed tubule is its own shell (tunica propria), consisting of three layers: the basal layer (stratum basale), the myoid layer (stratum myoideum) and the fibrous layer (stratum fibrosum). The basal layer (inner fibrous layer), located between the two basal membranes (spermatogenic epithelium and myoid cells), consists of a network of collagen fibers. The myoid layer is formed by myoid cells containing actin filaments. Myoid cells provide rhythmic contractions of the tubular wall. The outer fibrous layer consists of two parts. Directly to the myoid layer adjacent non-cellular layer formed by the basement membrane of myoid cells and collagen fibers. Behind them is a layer consisting of fibroblast-like cells, adjacent to the basement membrane of the hemocapillary endothelial cells.
In the connective tissue between the seminiferous tubules are located hemocapillaries and lymphocapillaries, which ensure the exchange of substances between the blood and the spermatogenic epithelium. The selectivity of the entry of substances from the blood into the spermatogenic epithelium and the differences in the chemical composition of blood plasma and fluids from the seminiferous tubules allowed us to formulate an idea of the hemato-testicular barrier. The hemato-testicular barrier is the collection of structures located between the lumens of the capillaries and the seminiferous tubules.
The epithelium spermatogenic layer (epithelium spermatogenicum) has two main cell populations:
- spermatogenic cells (cellulae spermatogenicae) that are at different stages of differentiation (stem cells, spermatogonia, spermatocytes, spermatids and spermatozoa) and
- supporting cells, or sustentocytes (epitheliocytus sustentans), or Sertoli cells.
Both cell populations are in close morphofunctional communication.
The supporting cells (Sertoli cells) lie on the basement membrane, have a pyramidal shape and reach the apex of the lumen of the convoluted seminiferous tubule. Their nuclei have an irregular shape with invaginations, a three-membered nucleolus (the nucleolus, and two groups of perioatrial chromatin). The cytoplasm is particularly well developed agranular endoplasmic reticulum, the Golgi apparatus. There are also microtubules, microfilaments, lysosomes and special crystalloid inclusions. Inclusions of lipids, carbohydrates, lipofuscin are detected. On the lateral surfaces of the sustentocytes, bay-like depressions are formed, in which differentiated spermatogonia, spermatocytes and spermatids are located.
Between adjacent supporting cells, tight contact zones are formed, which divide the spermatogenic epithelium into two sections - the outer basal and the inner adluminal.
In the basal section, spermatogonia are located that have maximum access to nutrients from the blood capillaries.
Spermatocytes at the meiosis stage, as well as spermatids and spermatozoa, which do not have access to the tissue fluid and receive nutrients directly from Sertoli cells, are located in the adpulum.
Supporting epithelial cells create the microenvironment necessary for differentiating germ cells, isolate the germ cells from toxic substances and various antigens, and impede the development of immune responses. Thus, the sustentocytes are the major component of the hematotescular barrier. In addition, the sustentocytes are capable of phagocytosis of degenerating germ cells and their subsequent lysis with the help of their lysosomal apparatus.
Sertoli cells synthesize androgen binding protein (ASB), which transports the male sex hormone to spermatids. The secretion of ASB is enhanced under the influence of FSH adenohypophysis. Supporting epithelial cells have surface receptors for FSH, as well as receptors for testosterone and its metabolites.
There are two types of supporting cells - light and dark. Light supporting cells produce inhibin, a factor inhibiting the secretion of FSH by the adenohypophysis. Dark supporting cells produce a factor that stimulates the division of spermatogenic cells.
Generative function. Spermatogenesis
The formation of male germ cells (spermatogenesis) occurs in convoluted seminiferous tubules and includes 4 successive stages or phases: reproduction, growth, maturation and formation.
The initial phase of spermatogenesis is reproduction of spermatogonia occupying the most peripheral (basal) position in the spermatogenic epithelium. According to modern concepts, two types of cells can be distinguished among spermatogonia: 1) stem spermatogonia of type A, which are subdivided into two subpopulations: long-lived, reserve stem cells and rapidly renewed half-stem cells that divide once during a cycle of spermatogenic epithelium, 2) differentiating spermatogenic cells Type A and Type B.
Stem cells are located in the basal part of the tubule isolated from other spermatogonia. Morphologically, in the population of stem A-spermatogonia, light and dark cells are distinguished. Both cells are characterized by the predominance of decondensed chromatin in the nuclei and the location of the nucleoli around the nuclear membrane. However, in dark type A cells, the degree of chromatin condensation is greater than in light cells. Dark cells are referred to as “reserve” slow-renewing stem cells, and light cells - to half-stem fast-renewing cells. Stem cells are characterized by the presence of oval nuclei with diffusely distributed chromatin, one or two nucleoli, a high content in the cytoplasm of ribosomes and a policy, a small number of other organelles.
Some of the type A stem cells during division do not complete cytokinesis and remain connected by cytoplasmic bridges, i.e. form syncytium. The appearance of such paired spermatogonies indicates the beginning of the differentiation process of male germ cells. Further division of such cells leads to the formation of chains or groups of spermatogonia, connected by cytoplasmic bridges. Type B cells have larger nuclei, the chromatin in them is not dispersed, but assembled in clumps.
In the next period (growth period), the spermatogonia stops sharing mitosis, increases in volume and enters the first division of meiosis. This is the beginning of their differentiation into 1st order spermatocytes, and the beginning of the third period, the period of maturation. Syncytial groups of spermatogonia begin to move to the adrenal zone of the spermatogenic epithelium. In the first division of meiosis, conjugation of homologous chromosomes and crossing-over occur in cells. Each of the two daughter cells - spermatocytes of the 2nd order contains a haploid number of chromosomes (23 in humans).
The second division of maturation begins immediately after the first, and occurs as normal mitosis without reduplication of chromosomes. In the anaphase of the second division, the maturation of a second-order spermatocyte dyad is separated into monads, or single chromatids, diverging to the poles. As a result, spermatids get as many monads as there were dyads in the nuclei of second-order spermatocytes, i.e. haploid number. Spermatocytes of the 2nd order are smaller than spermatocytes of the 1st order, and are located in the middle and more superficial layers of the epitheliospermatogenic layer.
Thus, each initial spermatogonia gives rise to 4 spermatids with haploid set of chromosomes. Spermatids are no longer dividing, but they are transformed into mature spermatozoa through complex restructuring. This transformation constitutes the fourth phase of spermatogenesis - the period of formation, or spermatogenesis.
Spermatids are small rounded cells with relatively large nuclei. Accumulating around the tops of the supporting cells, the spermatids are partially immersed in their cytoplasm, which creates conditions for the formation of spermatozoa from spermatids. The core of spermatids gradually compacted and flattened.
In the spermatids, the Golgi apparatus is located near the nucleus, the centrosome and small mitochondria accumulate. The process of sperm formation begins with the formation of a compacted granule in the zone of the Golgi apparatus - an acroblast adjacent to the surface of the nucleus. Subsequently, the acroblast, increasing in size, envelops the nucleus in the form of a cap, and in the middle of the acroblast, a compacted body is differentiated. This structure is called the acrosome. It lies at the end of the transforming spermatid, which faces the supporting cell. A centrosome consisting of two centrioles moves to the opposite end of the spermatids. The proximal centriole is adjacent to the surface of the nucleus, and the distal centreol is divided into two parts. A flagellum (flagellum) begins to form from the front of the distal centriole, which then becomes the axial filament of the developing spermatozoon. The posterior half of the distal centriole takes the form of a little ring. Moving along the flagellum, this ring defines the posterior border of the middle or connecting part of the spermatozoon.
Cytoplasm, as the tail grows, slips off the nucleus and concentrates in the connecting part. Mitochondria are arranged in a spiral fashion between the proximal centriole and the ringlet.
The cytoplasm of spermatids during its transformation into sperm is greatly reduced. In the head region, it is preserved only as a thin layer covering the acrosome; a small amount of cytoplasm remains in the area of the binder section and, finally, it covers the flagellum with a very thin layer. Part of the cytoplasm is discharged and decomposed in the lumen of the seminiferous tubule or absorbed by the supporting cells. In addition, these cells produce fluid that accumulates in the lumen of the convoluted seminiferous tubule. The formed spermatozoids are released into this fluid, being released from the tops of the supporting cells, and with it go into the distal parts of the tubule.
The process of spermatogenesis in general lasts about 75 days in humans, but proceeds in a wave-like manner throughout the convoluted tubule. Therefore, on each segment of the tubule there is a certain set of spermatogenic epithelium cells.
The epithelium-spermatogenous layer is extremely sensitive to damaging effects. With various intoxications, avitaminosis, malnutrition and other conditions (especially when exposed to ionizing radiation), spermatogenesis is weakened or even stopped, and the spermatogenic epithelium atrophies. Similar destructive processes develop during cryptorchidism (when the testes do not descend into the scrotum, remaining in the abdominal cavity), the body remains in an environment with high temperature, feverish conditions, and especially after ligation or transection of the vas deferens. The destructive process in this case primarily affects the forming spermatozoa and spermatids. The latter swell, often merge into characteristic rounded masses - the so-called seed balls, floating in the lumen of the tubule. Since the lower layers of the spermatogenic epithelium (spermatogonia and spermatocytes of the 1st order) are preserved for a longer time, the restoration of spermatogenesis after the termination of the damaging agent is sometimes possible.
The destruction described above is limited only by the spermatogenic layer. The supporting cells in these circumstances are preserved and even hypertrophied, and the glandulocytes often increase in number and form large aggregations between the desolate seminiferous tubules.
Endocrine functions of the testes and hormonal regulation of the male reproductive system
In the loose connective tissue between the loops of convoluted tubules are interstitial cells - glandulocytes, or Leydig cells, accumulating here around the blood and lymphatic capillaries. These cells are relatively large, round or polygonal in shape, with acidophilic cytoplasm vacuolated around the periphery, containing glycoprotein inclusions, as well as glycogen clumps and protein crystalloids in the form of sticks or ribbons. With age, the pigment begins to be deposited in the cytoplasm of the interstitial cells. A well-developed smooth endoplasmic reticulum, numerous mitochondria with tubular and vesicular cristae indicate the ability of interstitial cells to produce steroid substances, in this case the male sex hormone - testosterone. A high concentration of testosterone in the seminiferous tubules is provided by ASB synthesized by Sertoli cells.
The activity of Leydig cells is regulated by the luteinizing hormone (LH) of the adenohypophysis.
Both gonadal functions (generative and endocrine) are activated by adeno-pituitary gonadotropins - follitropin (follicle-stimulating hormone, FSH) and lyutropin (luteinizing hormone, LH). Follitropin mainly affects the epithelio-spermatogenic layer, the germinative function of the testis, and the functions of the glandulocytes are regulated by lyutropin. However, in reality, gonadotropin interactions are more complex. It has been proven that the regulation of the germinative function of the testis is carried out by the combined influence of follitropin and lutropin.
Peptide inhibins inhibit the follicle-stimulating function of the pituitary (by the mechanism of negative feedback), which leads to a weakening of the influence exerted on the testes by follitropin, but does not prevent the action of lyutropin on it. Thus, inhibin regulates the interaction of both gonadotropins, which is manifested in their regulation of the activity of the testicle.
The seminiferous tracts form the system of testicular tubules and its appendages, along which sperm (spermatozoa and fluid) are advanced into the urethra.
The outflow tracts begin with testicular tubules (tubuli seminiferi recti) flowing into the testicular network (rete testis), located in the mediastinum (mediastinum). Twelve to fifteen convoluted outgoing tubules (ductuli efferentes testis), which are connected to the duct of the appendage (ductus epididymidis) in the region of the head of the appendage, depart from this network. This duct, writhing many times, forms the body of the appendage and in the lower caudal part of it passes into the direct vas deferens (ductus deferens), rising to the exit from the scrotum, into the inguinal canal, and then reaching the prostate gland where it flows into the urethra.
All the vas deferens are built according to a general plan and consist of mucous, muscular and adventitial membranes. The epithelium lining these tubules reveals signs of glandular activity, especially pronounced in the head of the appendage.
In the direct testicular tubules, the epithelium is formed by prismatic cells. The tubules of the testicular network in the epithelium are dominated by cubic and flat cells. In the epithelium of the vas deferens, groups of ciliary cells alternate with apocrine-secreting glandular cells.
In the epididymis, the epithelium of the duct becomes two-row. It consists of high prismatic cells that carry stereocilia at their apical tips, and intercalated cells are located between the basal parts of these cells. The epithelium of the duct of the epididymis is involved in the production of a fluid that dilutes sperm during the passage of spermatozoa, as well as in the formation of glycocalyx, a thin layer that covers the spermatozoa. The removal of glycocalyx during ejaculation leads to the activation of spermatozoa (accumulation). At the same time, the appendage of the testis turns out to be a reservoir for accumulating sperm.
The promotion of sperm through the vas deferens is provided by the contraction of the muscular layer formed by a circular layer of smooth muscle cells.
The duct of the appendage then passes into the vas deferens (ductus deferens), in which the muscular membrane is significantly developed, consisting of three layers — the inner longitudinal, middle circular and outer longitudinal. In the thickness of the muscle membrane is the nerve plexus, formed by a cluster of ganglion cells innervating bundles of smooth muscle cells. Cuts of these cells provide ejaculation of sperm. In connection with the significant development of the muscular coat, the mucous membrane of the vas deferens collects in longitudinal folds. The distal end of this duct is ampule-like expanded. Outside, the seminal paths are covered throughout with a connective tissue adventitious membrane.
Below the junction of the vas deferens and seminal vesicles, the ejaculatory duct (ductus ejaculatorius) begins. It penetrates the prostate gland and opens into the urethra. Unlike the vas deferens, the ejaculatory duct does not have such a pronounced muscular membrane. The outer shell of it grows together with the connective tissue stroma of the prostate.
Vascularization Blood supply of the testis is provided through the branch of the internal spermatic artery, which is part of the spermatic cord, into the mediastinum, where it branches into a network of capillaries penetrating the connective tissue septa into the lobules and braiding loops of the convoluted seminiferous tubules. Interstitial cells accumulate around these capillaries.
Lymphatic capillaries also form a network between the testicle canaliculi, and then form the outgoing lymphatic vessels.
Innervation. Nerve fibers, both sympathetic and parasympathetic, penetrate the testis along with blood vessels. Numerous sensory nerve endings are scattered in the testicular parenchyma. Nerve impulses entering the testis can have some influence on its generative and endocrine functions, but the main regulation of its activity is carried out by the humoral effects of the gonadotropic hormones of the adenohypophysis.
Age changes. The generative function of the testis begins at the prepubertal age, but during this period spermatogenesis stops in the initial stages. Full completion of spermatogenesis (with the formation of spermatozoa) occurs only after reaching puberty - puberty. In the newborn, the seminiferous tubules still have the form of continuous cellular cords consisting of supporting cells and spermatogonia. This structure of the seminiferous tubules retain during the first 4 years of the postnatal period of development of the boy. The lumen in the seminiferous tubule appears only by 7–8 years of life. At this time, the number of spermatogonia increases significantly, and around 9 years of age, single 1st order spermatocytes appear among them, indicating the beginning of the second stage of spermatogenesis, the growth stage. Between 10 and 15 years, the seminiferous tubules become convoluted: spermatocytes of the 1st and 2nd order are found in their gaps, and even spermatids, and the supporting cells reach full maturity. By the years 12-14, the growth and development of the excretory ducts and the epididymis increase noticeably, which indicates that the male sex hormone enters the circulation in a fairly high concentration. Accordingly, a large number of large interstitial cells are found in the testes.
The age-related involution of the testis in men occurs between 50 and 80 years. It is manifested in the increasing weakening of spermatogenesis, the growth of connective tissue. However, even in old age, spermatogenesis is retained in some of the seminiferous tubules and their structure remains normal.
In parallel with the progressive atrophy of the epitheliospermatogenic layer, the destruction of glandulocytes increases, as a result of which the production of the male sex hormone weakens, and this in turn turns out to cause age-related atrophy of the prostate gland and partially the external genitalia. With age, the pigment begins to be deposited in the cytoplasm of the interstitial cells.
Additional glands of the male reproductive system
The accessory glands of the male reproductive system include the seminal vesicles, prostate gland, bulbourethral glands.
Seminal vesicles develop as protrusions of the wall of the vas deferens in its distal (upper) part. These are paired glandular organs, which produce a liquid mucous secretion, a weakly alkaline reaction, rich in fructose, which is added to the sperm and thins it. In the wall of the bubbles there are shells, the boundaries between which are not clearly expressed: mucous, muscular, adventitial. The mucous membrane is collected in numerous branched folds, merging in places with each other, as a result of which it acquires a cellular appearance. The mucous membrane is covered with a single-layer columnar epithelium lying on a thin basement membrane. In the lamina propria of the mucosa there are many elastic fibers. In the mucous membrane are the terminal sections of the glands of the alveolar type, consisting of mucous exocrinocytes (exocrinocytus mucosus).
The muscular membrane is well defined and consists of two layers of smooth muscle cells - the inner circular and the outer longitudinal. Adventitia is composed of dense fibrous connective tissue with a high content of elastic fibers.
Prostate gland [Greek prostates, standing in front], or the prostate, (or the male second heart) is a muscular-glandular organ, covering the part of the urethra (urethra), into which the ducts of numerous prostatic glands open.
Development. In a human embryo, it begins on the 11th — 12th week of embryogenesis, and 5-6 strands grow from the epithelium of the urethra into the surrounding mesenchyme. In the first half of human prenatal embryogenesis, mainly alveolar-tubular prostatic glands develop from expanding epithelial cords, and in the second half, the growth of smooth muscle tissue and connective tissue layers of the prostate gland prevails. Gaps in epithelial cords appear at the end of the pre-fetus period of development of the embryo. Apart from these glands, small glands arise from the epithelium of the urethra, which are located between the prostate uterus and the vas deferens duct.
Structure. The prostate gland is a lobulated gland covered with a connective tissue capsule. Its parenchyma consists of numerous individual mucous glands, the excretory ducts of which open into the urethra. The glands are located around the urethra in three groups: central, peripheral and transitional.
The central group consists of small glands in the composition of the mucous membrane immediately around the urethra. The intermediate group in the form of a ring lies in the connective tissue of the submucosa.
The peripheral group consists of the prostate gland itself. It occupies the rest of the body. The terminal sections of the alveolar-tubular prostate glands are formed by high mucous exocrinocytes (exocrinocytus mucosus), between the bases of which there are small intercalated cells. The excretory ducts, before entering the urethra, expand in the form of ampoules of irregular shape, lined by a multi-row prismatic epithelium. The muscular-elastic stroma of the gland (stroma myoelasticum) is formed by loose fibrous connective tissue and powerful bundles of smooth muscle cells, radially diverging from the center of the prostate gland and dividing it into lobules. Each lobule and each gland is surrounded by longitudinal and circular layers of smooth muscle cells, which, shortening, eject secretions from the prostate glands at the time of ejaculation.
At the confluence of the vas deferens into the urethra in the prostate gland is located the seed tubercle (colliculus seminalis). From the surface it is lined with transitional epithelium, and its base is made up of connective tissue, rich in elastic fibers, and smooth muscle cells. Due to the presence of numerous nerve endings, the seminal tubercle is most sensitive. The stimulation of the seed tubercle causes his erection, thereby preventing the ejaculate from entering the bladder.
Behind the seed tubercle is the prostate uterus (utriculus prostaticus), which opens onto the surface of the seed tubercle.
The functions of the prostate gland are diverse. The secretion produced by the prostate that is released during ejaculation contains immunoglobulins, enzymes, vitamins, citric acid, zinc ions, etc. The secret is involved in the dilution of the ejaculate. The prostate gland has not only external, but also internal secretion. The structure and function of the prostate are controlled by pituitary hormones, androgens, estrogens, and other steroid hormones. Different parts of the gland have different sensitivities, in particular, androgens stimulate the posterior part of the gland, and estrogens, the anterior part. The prostate is highly sensitive to testicular hormones. This gland is dependent on testosterone testes and atrophies after castration. The peripheral zone is regulated by androgens, while the central one is more sensitive to the effects of estrogen. Testosterone enters the cells by diffusion, where it undergoes active metabolism and transformation into dihydrotestosterone (DHT).
After binding in the cell with a specific androgen receptor, DHT penetrates the nucleus, where it activates the formation of specific enzymes and prostate proteins. In addition, this gland affects the sexual differentiation of the hypothalamus (it participates in determining its differentiation according to the male type), and also produces a factor that stimulates the growth of nerve fibers.
Vascularization The blood supply to the prostate is due to the branches of the artery of the rectum and bladder. The venous system consists of numerous anastomosing veins, forming the vesicular prostatic venous plexus.
Age changes. The prostate gland during a person’s life undergoes an age-related restructuring associated with a decrease in the formation of sex hormones and manifested by shifts in the ratio between the glandular epithelium, connective tissue and smooth muscle cells of this organ.
The secretory sections of the prostate gland of the child have epithelium consisting of two types of cells - high and low epithelial cells. The connective tissue forms massive bundles along the outflow ducts and is significantly compacted around the secretory sections. It is dominated by fibroblasts, macrophages and collagen fibers. There are relatively few smooth muscle cells in the stroma.
During puberty in the cytoplasm of glandular cells of the terminal sections, secretory processes are enhanced. The epithelium becomes high. During the period of the greatest functional activity (at the age of 20-35 years) in the prostate gland secretory elements predominate over connective tissue, the synthesis of glycogen, glycosaminoglycans and glycoproteins increases.
Later (at 35–60 years) some glandular lobules begin to atrophy, and the connective tissue grows and thickens. The glandular epithelium gradually becomes low. Prostate nodules (sand) are formed and accumulate in the cavity of the secretory regions, which are especially common in old age.
Bulbourethral glands (glands of Littre) in their structure are alveolar-tubular, opening their ducts in the upper part of the urethra. Their end sections and excretory ducts have an irregular shape. The terminal tubular-alveolar regions are interconnected in places and consist of mucous cells (exocrinocytus mucosus). In the dilated alveoli of these glands, the epithelium is most often flattened; in the rest of the gland, it is cubic or prismatic. Epithelial cells are filled with mucoid droplets and peculiar rod-shaped inclusions. Between the end sections are layers of loose fibrous, unformed connective tissue containing bundles of smooth muscle cells.
The penis is a copulatory organ. Its bulk is formed by three cavernous (cavernous) bodies, which, filled with blood, become rigid and provide an erection. Outside, the cavernous bodies are surrounded by the tunica albuginea, formed by dense fibrous connective tissue. This fabric is replete with elastic fibers and contains a significant amount of smooth muscle cells. In the middle of the lower cavernous body passes the urethra, through which semen is secreted. It is divided into the prostate part (pars prostatica), the membranous part (pars membranacea) and the spongy part (pars spongiosa).
The urethra has a well-defined mucous membrane. Its epithelium in the prostate gland is transitional, in the membranous part it is a multi-row prismatic, and starting from the scaphoid fossa in the spongy part, the urethral epithelium becomes stratified and flatters the signs of keratinization. In the multi-row epithelium there are numerous goblet and few endocrine cells. Under the epithelium is its own plate of the mucous membrane, rich in elastic fibers. In the loose fibrous tissue of this layer passes the network of venous vessels, having a connection with the cavities of the cavernous body of the urethra. In the mucosa of the urethra are small mucous glands. In the submucosa, there is a network of wide venous vessels.
The muscular membrane of the urethra is well developed in its prostatic part, where it consists of the internal longitudinal and external circular layers of smooth myocytes. When the membranous part of the urethra passes into its cavernous part, the muscle layers gradually become thinner and only single bundles of muscle cells are preserved.
The base of the glans penis consists of a dense fibrous connective tissue, which has a network of anastomosing veins, overflowing with blood during erection. In their thick wall are longitudinal and circularly arranged bundles of smooth muscle cells. The skin covering the head of the penis is thin. It contains the sebaceous (preputial) glands (gll. Sebacea preputiales).
Vascularization Arteries that bring blood to the cavernous bodies have a thick muscular layer and a wide lumen. The artery of the penis, supplying it with blood, splits into several large branches that pass through the septa of the cavernous tissue. With a quiet state of the penis, they are spiral-shaped and therefore are called curled or cochlear (aa. Helicinae). In the inner membrane of these arteries there are thickenings consisting of bundles of smooth muscle cells, as well as collagen fibers. These bulges are a kind of valves that close the lumen of the vessel. The veins are also distinguished by a thick wall, a well-pronounced muscular layer in all shells: longitudinal - in the inner shell, circular - in the middle and longitudinal - in the outer adventitian sheath. The vascular cavities of the cavernous bodies, the network of which is located between the arteries and the veins, have very thin walls lined with endothelium. The blood from the cavities leaves the small thin-walled vessels, flowing into the deep veins. These vessels play the role of valves or sluices, since during an erection the wall of the vein contracts and clamps their lumen, which prevents the outflow of blood from the cavities. In the vascular system of the penis, typical arterio-venular anastomoses were also detected.
Innervation. Sympathetic non-myelinated fibers in the penis form a plexus innervating bundles of smooth muscle cells in the walls of blood vessels and in the septa between the vascular cavities of the cavernous bodies. Numerous receptors are scattered in the skin of the penis and the mucous membrane of the urethra. Among them are free branching endings, lying in the epithelium of the glans penis and foreskin, as well as in the subepithelial tissue.
Nonfree encapsulated endings are especially numerous and varied in the tissues of the penis. These include tactile bodies in the papillary layer of the foreskin and the head of the penis, genital bodies, lamellar in the deep layers of the connective tissue of the penis and in the albumin of the cavernous bodies.