Development of the reproductive system

The development of the reproductive system is the part of embryonic growth that results in the sex organs and contributes to sexual differentiation.

The reproductive organs develop from the intermediate mesoderm and are preceded by more primitive structures that are superseded before birth.

The paramesonephric duct gives rise to the female fallopian tubes, uterus, cervix, and upper part of the vagina.

This continues to grow caudally until it opens into the ventral part of the cloaca; beyond the pronephros it is termed the mesonephric duct.

A large part of the head end of the mesonephros atrophies and disappears; of the remainder the anterior tubules form the efferent ducts of the testicle; while the posterior tubules are represented by the ductuli aberrantes, and by the paradidymis, which is sometimes found in front of the spermatic cord above the head of the epididymis.

Each arises on the lateral aspect of the corresponding mesonephric duct as a tubular invagination of the cells lining the abdominal cavity.

This fusion of the paramesonephric ducts begins in the third month, and the septum formed by their fused medial walls disappears from below upward.

The ostium of the fallopian tube remains from the anterior extremity of the original tubular invagination from the abdominal cavity.

A ring-like outgrowth of this epithelium occurs at the lower end of the uterus and marks the future vaginal fornix.

Via the rete testis, the seminiferous tubules become connected with outgrowths from the mesonephros, which form the efferent ducts of the testicle.

The remainder of the vesico-urethral portion forms the body of the bladder and part of the prostatic urethra; its apex is prolonged to the umbilicus as a narrow canal, the urachus, which later is obliterated and becomes the median umbilical ligament of the adult.

The prostate originally consists of two separate portions, each of which arises as a series of diverticular buds from the epithelial lining of the urogenital sinus and vesico-urethral part of the cloaca, between the third and fourth months.

These buds become tubular, and form the glandular substance of the two lobes, which ultimately meet and fuse behind the urethra and also extend on to its ventral aspect.

Until about the ninth week of gestational age,[4] the external genitalia of human males and females look the same, and follow a common development.

In placental mammals, the urogenital folds become the ventral aspect of the penis in the male and the labia minora (primates including humans)/labia vulvae (non-primates) in the female.

[8][10] There is initially a cloacal membrane, composed of ectoderm and endoderm, reaching from the umbilical cord to the tail, separating the cloaca from the exterior.

The remainder of the phallic portion is for a time tubular, and then, by the absorption of the urogenital membrane, it establishes a communication with the exterior.

Meanwhile, the urethral plate of the glans breaks down centrally to form a median groove continuous with the primitive ostium.