Genitourinary apparatus in ontogenesis

The urinary and reproductive systems are interrelated in their development. In a person from the embryonic structures of some organs, which form as urinary organs, later genitals are formed.

In the lower vertebrates, three generations of excretory organs are distinguished, replacing each other: the preference, the primary kidney and the terminal kidney.

Preference (pronephros) - the most simple form of excretory organs, it is laid in embryos of all vertebrate species of fish. It is a paired organ consisting of several secretory tubules, or protonefrids. At one end of the tubule there is a funnel that opens into the body cavity, and the other end of the tubule is connected to the excretory duct along the body. The right and left ducts in the caudal part of the body open outward or flow into the end section of the digestive tube. Near the funnels of protonephridia are the vascular glomeruli, where the filtration of the liquid takes place, which first separates into the body cavity, and then enters the lumen of the tubule.

In embryos of higher vertebrates, the laying of preference is very early reduced. To replace it, the second generation of excretory organs is laid-the primary kidney.

The primary kidney (mesonephros), or the volphic body, is a paired organ, which is placed caudally above the preference and consists of segmental convoluted tubules, or mesonephridia. In higher vertebrates, these tubules at one end start blindly and have the appearance of a double-walled cup (capsule). In the capsule vascular glomerulus is invaded (glomerulus). Together they form a renal corpuscle (corpusculus renis). The other end of the canal is connected to the remaining duct of the preference, which becomes the excretory duct of the primary kidney - the ductus mesonephricus. The primary kidney is pawned and functions as a secretory organ in all vertebrates in the embryonic period, and in adult individuals - only in cyclostomes and some fish. In higher vertebrates, the primary kidney and its meso-neural duct function for a certain time, and then are partially reduced. The remaining parts of the primary kidney serve as an embryo for the development of certain genital organs.

The lateral duct of the primary kidney in parallel with it in the embryo of vertebrates from the cells lining the body cavity, develops a paramedesonephalic duct (ductus paramesonephricus), or mullerian duct. The cranial ends of these ducts open into the body cavity, and caudal connect to one another in the common duct, which opens into the genitourinary sinus (sinus urogenitalis). From the parameconeural ducts, the female tubes and vagina are laid and developed in the female, and the appendages of the reproductive organs are found in the male. In place of the primary kidney is the third generation of excretory organs - the final kidney.

The final kidney (metanephros) is a paired excretory organ, later on the fetus is preplanned and the primary kidney. The final kidney is formed from the nephrogenic tissue and the proximal part of the ureteral outgrowth of the primary kidney duct. The final kidney functions as a urine-forming organ in higher vertebrates.

The system of genital organs in higher animals consists of the sex glands and the genital tract. The sex glands in vertebrate animals are paired, develop on the posterior wall of the body, medial to the primary kidney. Excretory pathways for sex cells are formed from the primary kidney duct (in males) or the parameconeural duct (in females).

In mammals, the gonads from the place of their laying are moved to the pelvic region. The ovaries remain in the cavity of the small pelvis, the testes (testes) in most mammals (except for some insectivores, cetaceans, etc.) come out of the abdominal cavity into the skin fold - the scrotum. From the anterior part of the cloaca in mammals the urogenital sinus is segregated, into which the sexual ducts open. In viviparous mammals, the urogenital sinus is transformed into the vestibule of the vagina. In males, the urogenital sinus stretches into the urethra.

In the genitourinary ducts in males also open the ducts of seminal vesicles, prostate and bulbourethral glands; in female individuals, large glands of the vestibule (vagina) are formed.

The formation of the uterus in placental mammals occurs by merging the most common rodents, elephants and some other animals of paired oviducts (double uterus) into a bifid uterus divided by a longitudinal partition (in some rodents, carnivores, pigs). In ungulates, cetaceans and insectivores, the fusion of the oviducts is such that a bicornic uterus is formed, and only in some bats and monkeys does the uterus have one cavity (simple uterus) that opens into the vagina.

A person in embryogenesis is laid, and then completely disappears preference. The primary kidney at a certain stage of development ceases to perform its function and is partially reduced. The remaining parts of the primary kidney serve as a source of development of some genital organs and their appendages. In the course of its development, the organs of the urinary and reproductive systems come into close anatomical relationships.

[1], [2]