Testes

a. Testes : The testes are a pair of mesodermal organs formed in the lower abdominal cavity and housed in a pouch called the scrotum. During early foetal life they develop inside the abdominal cavity and later descend into the scrotal sac through a passage called the inguinal canal. Each testis is oval, about 4-5 cm long, 2-3 cm wide and 3 cm thick.

Histology of Testis : Externally the testis is covered by a tough collagenous connective-tissue layer, the tunica albuginea; outside this lies an incomplete peritoneal covering, the tunica vaginalis, and internally, a thin, vascular and membranous layer, the tunica vasculosa. Fibrous septa arising from the tunica albuginea divide each testis internally into about 200–300 compartments called testicular lobules, each containing 1–4 highly coiled seminiferous tubules. Every seminiferous tubule is lined internally by cuboidal germinal epithelial cells (spermatogonia) along with a smaller number of large, pyramidal Sertoli (sustentacular) cells. The germinal epithelial cells undergo spermatogenesis to form spermatozoa, while the Sertoli cells provide nourishment to the developing sperm; the successive stages of spermatogenesis — spermatogonia (2n), primary spermatocyte (2n), secondary spermatocyte (n), spermatid (n) and sperm (n) — can all be seen within the tubule wall. Lying in the loose connective tissue between the seminiferous tubules are the interstitial cells or Leydig cells, which secrete the male hormone, androgen or testosterone.