Male Reproductive System
To understand the male reproductive system, one must know the external and internal structures, and the process of spermatogenesis (sperm production) including the physiologic pathway of the sperm cell.
The male external structures are the penis and the scrotum (a pouch which protects the testes). The penis consists of the glans (the head), and the shaft (the body). The glans is covered by a fold of skin called the foreskin (circumcision removes the foreskin). The scrotum surrounds and protects the two testes, internal structures also referred to as testicles.
The testes are the male gonads and contain hundreds of tiny seminiferous tubules where sperm cells are produced. The epididymis is a small oblong body which rests on the surface of the testes where sperm mature and are stored. The epididymis leads into the vas deferens (narrow tubes which carry sperm away from the testes). The vas deferens extends to join with the ducts of the two seminal vesicles (located on side of the prostate gland) to form the ejaculatory ducts which extend through the body of the prostate gland and empty into the urethra. The prostate gland surrounds the neck of the bladder (the structure that stores urine) and the urethra, (a thin tube which extends through the penis and carries semen and urine outside of the body, although not simultaneously). The Cowper's glands (also called the bulbourethral glands) are found on each side of the urethra, just below the prostate gland.
Process of Spermatogenesis
Spermatogenesis begins in the seminiferous tubules of the testes. Sperm pass into the epididymis where they mature and become motile so they are able to move through the vas deferens and into the seminal vesicles where they mix with seminal fluids, rich in fructose and other nutrients. The prostate gland and the Cowper's glands secrete fluids which also help to nourish and transport the sperm. This mixture of fluids and sperm is called semen, the fluid which is expelled from a man's penis during ejaculation. Sexual arousal can cause fluid from the Cowper's glands to be released prior to ejaculation. This fluid is called pre-ejaculatory fluid and does not contain sperm unless it is leftover from a previous ejaculation. Contrary to popular belief, there is little evidence to support that pre-ejaculatory fluid contains enough sperm to cause pregnancy.
Although men continue to produce sperm throughout their lives, testosterone production decreases at about 45-65 years of age.