Development of genito-urinary organs

Development of the bladder. The laying of the bladder in a 7 week embryo is associated with the transformation of the cloaca, allantoic (urinary sac) and caudal divisions of the primary kidney ducts. Cloaca frontal septum is divided into the anterior part - the urogenital sinus, part of which goes to the formation of the wall of the bladder, and the posterior section - the future rectum. Allantoic, primary kidney and parameconeural duct are connected with the genitourinary sinus. From the lower part of the allantois and the mouths of the ducts of the primary kidney, the bottom and triangle of the bladder form in the 2nd month of embryonic development. From the middle part of the allantoic body of the bladder is formed, and from its upper part - the urinary tract, which then turns into a fibrous cord - the middle umbilical ligament.

[1], [2]

Development of genital organs

At the embryo of the person first indifferent internal and external genital organs are laid, and then internal and external male or female sexual organs are formed in their final form.

The rudiments of indifferent gonads in a human embryo appear in the wall of the body cavity at the 4th week of embryonic development from the epithelial embryos, located anteriorly and medially from the lining of the right and left primary kidneys, from IV cervical to the V lumbar segments of the body. At the 5th week a groove is formed from the cells lining the body cavity. Then the groove deepens, its edges converge and it turns into a paramesonephral duct opening into the genitourinary sinus. The future sexual gland begins to form on the ventromedial surface of the primary kidney. In this place, on either side of the mesentery root, a cylindrical elevation is formed - the urogenital fold. In the future, each of these folds is divided by a longitudinal groove into the medial part - the genital fold, where the sexual gland is later formed, and the lateral part, which is the primary kidney, as well as the primary kidney and parameconeural duct.

At the 7th week the developing sex glands (gonads) begin to differentiate either into the testes or into the ovaries. When the testes are formed, the ducts of the primary kidneys are transformed into the outflowing ducts of the male gonads, and the parameconeural ducts are almost completely reduced. If the ovaries are formed, the uterine tubes, the uterus and part of the vagina develop from the parameconeural ducts, and the primary kidney ducts become vestigial formations. External genitals are laid in the embryo at the 7th week of embryonic development in an indifferent form: in the form of a tubercle, genital folds and ridges. Of these tabs, then develop male or female genital organs.

[3], [4], [5], [6], [7]

Development of internal male genital organs

At the 7th month of intrauterine development, a white membrane is formed from the connective tissue surrounding the developing male reproductive gland. By this time, the gland becomes more rounded, in it strands are formed, differentiating into the seminiferous tubules.

With the development of the male sex gland, outgoing tubules of the testicle are formed from the tubules of the primary kidney, and from the cranial part of the primary kidney duct is the duct of the epididymis. Several cranial tubules of the primary kidney are transformed into a pendant of the epididymis, and the caudally lying tubules are converted into an appendage of a testicle pendant. From the remaining part of the primary kidney duct (caudal to the epididymis), around which a muscle shell forms, a duct is formed. The distal part of the vas deferens extends and turns into an ampoule of the vas deferens, a seminal vesicle develops from the lateral protrusion of the duct. A vas deferens from the terminal narrowed section of the primary kidney duct, which opens into the male urethra - the male urethra.

The cranial end of the paramesonephalic duct is transformed into a testicle pendant, and from the merging caudal ends of these ducts a prostate appears. The rest of these ducts in male embryos is reduced.

The egg with its appendage and rudimentary formations do not remain at the place where they were laid, and in the process of development they move in the caudal direction - the process of lowering the testicles occurs (descensus testis). In this process, the main role is played by the testicular ligament. By the 3rd month of the intrauterine period the testicle is in the ileum, by the 6th month it comes to the inner ring of the inguinal canal. At the 7th-8th month, the testicle passes through the inguinal canal along with the vas deferens, vessels and nerves that form part of the testicle, which is formed during the descent process.

The prostate gland develops from the epithelium of the forming urethra in the form of cellular strands (up to 50), of which later lobules of the gland are formed. Bulbourethral glands develop from the epithelial processes of the spongy part of the urethra. The ducts of the prostate gland and bulbourethral glands open with their mouths in the places where these glands were laid during intrauterine development.

[8], [9]

Development of internal female genital organs

In the female embryo ovary, the connective tissue zone under the layer of the rudimentary epithelium is weaker than in the male sex gland. Cellular bands are less noticeable, the sex cells are scattered in the mesenchymal stroma of the organ. Some of these cells grow more active, they become larger, surrounded by smaller cells, initial - primordial - ovarian follicles are formed. In the future, the cerebral and brain substance of the ovary is formed. In the latter grow blood vessels and nerves. As the development of the ovaries also go down, but at a much shorter distance than the testicles. From the place of laying the ovaries are displaced along with the fallopian tubes into the pelvic region. Lowering the ovaries is accompanied by a change in the topography of the fallopian tubes, which move from the vertical position to the horizontal one.

With the development of the ovary, the remaining tubules and the duct of the primary kidney become rudimentary - the appendages of the female sex gland. The cranial tubules and the adjacent part of the duct are transformed into ovarian adnexa (nadyaichnik), and caudal ones - into the parasite. Remains of the primary kidney duct can be preserved as a continuous or intermittent cuff lying on the side of the uterus and vagina, this is the longitudinal duct of the ovary adnexa (ductus ductus epoophori longitudinalis).

From the parameconeural ducts, the uterine tubes develop, and the uterus and the proximal vagina are formed from the distal, fused parts. From the genitourinary sinus, the distal vagina and its vestibule are formed.

Development of external genital organs

At the 3rd month of intrauterine development, an anterior tubercle appears anterior to the cloacic membrane from the mesenchyme. At the base of the genital tubercle in the direction of the anal opening is the urogenital (urethral) groove, which is limited from both sides by the genital folds. On both sides of the genital tubercle and genital folds are formed a semilunar form of the eminence of the skin and subcutaneous tissue - the genital beads. These formations represent an indifferent laying of the external genital organs, from which later external male or female genital organs develop.

[10]

Development of external male genital organs

In male embryos, indifferent primordia undergo complex changes. The sexual tubercle begins to grow rapidly and extend, turning into cavernous bodies of the penis. On the lower (caudal) surface, the sexual folds become higher. They restrict the urogenital (urethral) gap, which turns into a groove. Then, as a result of the fusion of the edges of the groove, the male urethra and the spongy body of the penis are formed. During growth, the urogenital opening from the original position near the root of the penis moves to the distal end of the penis.

The place of closure (adhesion) of the urethral groove remains in the form of a hem, called the suture of the penis. Simultaneously with the formation of the male urethra, the foreskin is formed over the distal end of the penis. This is due to the development around the glans penis of the skin fold.

The sex rollers become more convex, especially in the caudal divisions, they converge and coalesce along the middle line. On the site of the fusion of the genital pads there is a seam of the scrotum, which extends from the root of the penis to the anus through the entire crotch.

[11]

Development of external female genital organs

In female embryos, the sexual tubercle is transformed into a clitoris. Sexual folds grow and turn into small labia, bounding the urogenital slit from the sides, which opens into the genitourinary sinus. The distal part of the sexual fissure becomes wider and turns into the vestibule of the vagina, where the female urethra and vagina open. The vaginal opening towards the end of the intrauterine development becomes much wider than the opening of the urethra. The sex rollers are transformed into large labia, in which a significant amount of fat accumulates, then they cover the small labia.

[12]