The testis is located in the scrotum and consists of convoluted seminiferous tubules enclosed by the tunica albuginea, a fibrous capsule of connective tissue. The seminiferous tubules are lined by seminiferous epithelium. At the base of this epithelium are, at regular intervals, the Sertoli (sustentacular) cells, which have large oval nuclei. The seminiferous epithelium further contains cells undergoing spermatogenesis; the least mature cells (spermatogonias) are located at the base of the epithelium, more matured cells (spermatogonias, spermatocytes, round spermatids, elongated spermatids) move towards the lumen, and the most mature cells, the spermatozoa, are released at the lumen. In the interstitial space between the seminiferous tubules are Leydig (interstitial) cells, which have abundant, eosinophilic cytoplasm, and blood vessels. In the mouse, the testes are freely retractable into the abdominal cavity. The 4X micrograph is a cross section of a mouse testis, showing the seminiferous tubules, the interstitial space, and the tunica albuginea. The 10X and 20X micrographs depict the seminiferous tubules and the tunica albuginea at increasing detail. The 20X micrograph also shows the Leydig cells located in the interstitial space. The 40X micrograph presents Leydig cells and the cells present in the seminiferous epithelium.

(1) Identify the histological components of the testis.

(2) Describe the processes of spermatogenesis and spermiogenesis and understand the concept of a cycle of seminiferous epithelium and the duration of spermatogenesis.

(3) Describe the histological structure and function of a Sertoli cell and the concept of the 'blood-testis barrier'.

(4) Describe the histological structure and function of Interstitial cells (of Leydig).

Ovarium Frog ovarium mice