The mature male reproductive system performs two critical roles: producing steroid hormones-primarily testosterone-and manufacturing the male gametes, sperm, and their surrounding fluid, semen. Steroid hormones support sperm production, or spermatogenesis, and promote male secondary sex characteristics, like increased muscle mass and male pattern hair growth. Male reproductive anatomy centers on producing, maturing and delivering sperm to the female to fertilize an egg.
Development
Human male embryos uniquely carry an "XY" sex chromosome pair, while females carry an "XX" pair. During very early embryonic development, genes on the Y chromosome trigger a complex cascade of events that causes the primordial reproductive organs to develop along a male path, producing testes, male tubing and a penis rather than ovaries, female tubing and a vagina.
Puberty
Puberty-the beginning of sexual maturation-typically occurs later in boys than in girls. Pubertal increases in the secretion of the master hormone GnRH from the brain trigger the pituitary gland to release more luteinizing hormone (LH) and follicle stimulating hormone (FSH). These hormones cause the testes to produce more testosterone, triggering both sperm production and changes in appearance. In boys, puberty culminates in the ability to ejaculate mature sperm.
Anatomy
The male gonads, the testicles or testes, sit outside the body in a sac of skin called the scrotum. Immature sperm produced by the testes travel through a convoluted tube called the epididymis and into the vas deferens. A widened portion of the vas deferens, called the ampulla, flanked on either side by structures called seminal vesicles, acts as a storage site for mature sperm. The ampulla connects with the ejaculatory duct, which passes through the prostate gland to join the urethra, which carries sperm out through the penis.
Function
The pituitary hormone LH prompts the Leydig cells to produce testosterone, which in combination with FSH acts on the Sertoli cells of the testis to stimulate spermatogenesis. The testes produce immature sperm that cannot swim or fertilize an egg. In their passage through the epididymis, the sperm fully mature and gain fertilizing potential. The seminal vesicles and prostate add critical components to the semen, the nutritive fluid that carries the sperm.
Male Sexual Response
With sexual excitement, blood fills in spongy spaces in the penis called corpora cavenosa, causing an erection. During the phase called emission, contractions of the smooth muscle in the vas deferens push sperm into the urethra, while the prostate and seminal vesicles contract to add seminal fluid. At ejaculation, contractions of smooth muscles in the urethra propel the sperm and semen out of the penis.
References
- "Handbook of Pathophysiology"; Elizabeth Corwin; 2001
- "Endocrinology: An Integrated Approach"; S.S. Nussey and S.A. Whitehead; 2001
