Testis

Testis tissue is divided into hundreds of seminiferous tubules, tightly coiled structures where sperm develop. Stem cells along the tubule walls divide and differentiate into mature sperm over about 64 days, a process called spermatogenesis. Sertoli cells line the tubules, supplying nutrients and forming the blood-testis barrier that shields developing cells from immune attack.

Between the tubules lie interstitial Leydig cells, which produce the hormone testosterone in response to luteinizing hormone from the pituitary gland. Testosterone drives puberty, deepens the voice, increases muscle mass, and maintains sperm production. Follicle-stimulating hormone works alongside testosterone to keep Sertoli cells functioning properly.

The testes rest within the scrotum, which hangs outside the body to keep temperature a few degrees cooler than core body temperature—optimal for sperm viability. Muscles in the scrotal wall adjust distance from the body, contracting in cold weather or relaxing when warm. Once sperm mature, they travel to the epididymis, where they gain motility and are stored until ejaculation moves them through the vas deferens and out of the urethra.

hormone feedback loops regulate production. Rising testosterone levels signal the hypothalamus and pituitary to dial back gonadotropin release, maintaining balance. Illness, toxins, tight clothing, or fever can temporarily reduce sperm counts, while anabolic steroids can suppress natural testosterone, shrinking the testes.

Testicular health includes regular self-exams to detect lumps that could indicate cancer, prompt treatment for infections or injuries, and protecting the groin during sports. Advances in assisted reproductive technologies, hormone therapy, and cryopreservation provide options for individuals with fertility challenges.