Describe the structure of mammalian testis with the help of labelled diagram.

Explanation

Testes. They are the primary sex organs which develop in the abdominal cavity during early foetal life. They descend into the scrotum through inguinal canals during 7th month of development. There is a pair of testes that are suspended in the scrotum by the spermatic cords. A fibrous cord that extends from the caudal end of the testis to the scrotal wall is called gubernaculum. Each testis is oval in shape with a length of about 4 to 5 cm and a width of about 2 to 3 cm. The peritoneum, called mesorchium supports the testis.

1. Protective Coverings (Tunicae). The testis is surrounded · Soovad w o Avon by three layers. (a) The tunica yginalis is the outer covering of the testis. (b) The tunica albuginea is a fibrous covering surrounding the testis situated under the tunica vaginalis. (c) The tunica vasculosa consists of a network of capillaries supported by delicate connective tissue which lines the tunica albuginea. 2. Testicular Lobules. Each testis has about 250 compartments called testicular lobules. Fig. A part of transverse .section of mammalian testis. 3. Seminiferous Tubules. Each testicular lobule of testes has 1-3 highly cenvoluted seminiferous tubules (or crypts) which become straight on inner side called tubuli recti and open into network of tubules called rete testis. Wali of each seminiferous tubule is formed of a single layered germinal epithelium made of cuboidal epithelium. These constitute male germ cells or spermatogonia. There are present tall sertoli or sustentacular cells in between, which support developing germ cells and provide nourishment. They also secrete androgen binding protein (ABP) which concentrates testorterone in the tubules. Sertoli cells also secrete inhibin that supresses FSH synthesis. Sertoli cells also provide nourishment to the developing sperms. 4. Leydig.s cells or Interstitial cells. They constitute the endocrine portion of the testis, found between the seminiferous tubules in the connective tissue. They secrete androgens i.e., testosterone (male sex hormone). 5. Vasa efferentia. 10-12 fine ciliated ductules arise from rete testis, which carry sperms from rete testis into head or caput part of epididymis.