Topics: CNS, pituitary, testis, epididymis, prostate, seminal vesicles, scrotum, penis

The male reproductive system consists of a number of individual organs acting together to produce functional spermatozoa, and to deliver these spermatozoa to the female reproductive tract. The haploid germ cells originate in the testis and continue their maturation as they transit the epididymis. The vas deferens carries the spermatozoa from the epididymis to the ampulla, provides a site for the mixing of seminal vesicle secretions, and continues as the ejaculatory duct through the prostate, emptying into the prostatic urethra . The germ cells, mixed with ejaculatory secretions from the accessory sex glands (seminal vesicles, prostate, bulbourethral gland), then exit the body through the penile urethra. The entire system is dependent upon neuro-endocrine regulation from the pituitary and hypothalamus. Knowledge of the anatomy and embryological origins of each of the components of the male reproductive tract is important in developing a basic and thorough understanding of the system as a whole. Although the discussion of male reproductive anatomy and embryology in this chapter is confined to the human system, subsequent chapters will show that much of our understanding of reproductive biology has been gained from research using various experimental animal models.


Testis
The testis is central to the male reproductive system. It is the organ which generates the haploid germ cell by the process of spermatogenesis and it is the site of androgen production. The testis arises from the primitive gonad on the medial surface of the embryonic mesonephros. Primitive germ cells, which migrate to this region from the yolk sac, cause the coelomic epithelial cells to proliferate and form the sex cords. Formation of the sex cords gives this region a raised contour that is called the genital ridge. By the seventh week of fetal development, proliferation of the mesenchyme has separated the sex cords from the underlying coelomic epithelium. During the fourth month, the sex cords become U-shaped and their ends anastomose to form the rete testis.At this point, the primordial sex cells are referred to as pre-spermatogonia and the epithelial cells of the sex cords as Sertoli cells. The mesenchymal tissue in the interstitial space between the tubules gives rise to the Leydig cells that are the site of androgen production. The rete testis extends into the mesonephric tissue and will anastomose with some of the mesonephric tubules forming the efferent ducts which communicate with the epididymis (discussed below). The sex cords will become the seminiferous tubules, although the tubules do not develop a lumen until after birth.

The testis develops abdominally and successful descent into the scrotum is essential for fertility. The scrotum is formed as coelomic epithelium penetrates the abdominal wall and protrudes into the genital swelling as the processus vaginalis. An outgrowth of each layer of the abdominal wall is carried with this epithelium, giving rise to the fascial layers of the scrotum.

The testis then descends behind the processus vaginalis and the layers of fascia covering the testis on each side, with the overlying skin of the genital swelling, fuse to form the scrotum.