Describe the histologic organization of the testes' seminiferous tubules.

• A. Seminiferous tubules lined by Leydig cells.
• B. Seminiferous tubules lined by germ cells at various stages with Sertoli cells; interstitial Leydig cells secrete testosterone.
• C. Tubules lined by simple squamous epithelium.
• D. Tubules continuous with epididymal ducts lined by pseudostratified epithelium.

Answer: (B)

The seminiferous tubules contain germ cells at various stages of development arranged along a supporting framework of Sertoli cells, with testosterone-producing Leydig cells in the surrounding interstitial tissue. Within each tubule, germ cells progress from spermatogonia near the basal lamina to primary and secondary spermatocytes, then to spermatids and finally mature spermatozoa released into the lumen. Sertoli cells extend from the basal lamina to the lumen, nourish and regulate developing germ cells, phagocytose residual bodies, and participate in forming tight junctions that create a barrier between basal and adluminal compartments. The interstitial Leydig cells are outside the tubules and secrete testosterone in response to LH, supporting spermatogenesis and secondary sexual characteristics. If a description suggested the tubules are lined by Leydig cells, or by simple squamous epithelium, or that they connect directly to epididymal ducts with pseudostratified epithelium, those points don’t fit the actual architecture: Leydig cells are not lining the tubules, the seminiferous epithelium is specialized for germ cell development, and the epididymis is a separate structure with its own lining.