Mesonephric duct

It is an important structure that plays a critical role in the formation of male reproductive organs.

It also serves as the primordium for male urogenital structures including the epididymides, vasa deferentia, and seminal vesicles.

In a male, they develop into a system of connected organs between the efferent ducts of the testis and the prostate, namely the epididymis, the vas deferens, and the seminal vesicle.

Testosterone binds to and activates androgen receptor, affecting intracellular signals and modifying the expression of numerous genes.

In the female, with the absence of anti-Müllerian hormone secretion by the Sertoli cells and subsequent Müllerian apoptosis, the mesonephric ducts regress, although inclusions may persist.

Diagrams to illustrate the changes in the cloaca in mammals during development. A , early embryonic stage, showing the cloaca receiving the urinary bladder, the rectum, and the Wolffian duct, as in the lower vertebrates. B , later stage, showing the beginning of the fold which divides the cloaca into a ventral urogenital sinus which receives the urinary bladder , Wolffian ducts, and ureters , and into a dorsal part which receives the rectum . C , further progress of the fold, dividing the cloaca into urogenital sinus and rectum; the ureter has separated from the Wolffian duct and is shifting anteriorly. D , completion of the fold, showing complete separation of the cloaca into ventral urogenital sinus and dorsal rectum.