Q.What is the composition of semen ?

The male reproductive system centres on the paired testes, each divided by internal septa into 200-250 lobules containing seminiferous tubules, the site of sperm production, which alone make up about 80% of testicular tissue. The tubule wall is lined by Sertoli (nurse) cells, which nourish developing sperm and secrete inhibin (a negative-feedback hormone that regulates sperm output), while Leydig (interstitial) cells sitting between the tubules secrete testosterone, the androgen that drives spermatogenesis. The testes sit outside the abdominal cavity in the scrotum, a skin sac that keeps them 2-3 degrees C cooler than internal body temperature — a genuine requirement, since viable sperm cannot form at normal body heat; a testis that fails to descend (cryptorchism) can cause sterility if not corrected early. Sperm travel from the tubules through the rete testis and vasa efferentia into the epididymis, where they are stored and physiologically mature, then on through the vas deferens and ejaculatory duct to the …