Human Reproduction

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Reproduction is the only way nature has of preventing human life from becoming extinct.
The male reproductive system includes the testes, the vas deferens, certain glands (prostate, seminal vesicles and Cowper's glands), and the penis. The testes are two oval shaped bodies included in a sac, the scrotum, outside the body. Inside each of the testes are many tightly coiled tubes called the seminiferous tubules. The seminiferous tubules empty into ducts that lead to a structure called the epididymis, which is a convoluted tubule. The sperm pass from the epididymis into a long tube called the vas deferens. The vas deferens carries sperm from the testes to the urethra, the tube that leads out of the body. The two vas deferens open to the urethra through the prostate gland, which is a short distance from the urethra's opening into the bladder. The prostate gland is a small muscular gland about the size of a walnut. It produces a fluid that mixes with sperm before sperm leaves the body. The seminal vesicles are two glands located at the top of the prostate gland. They secrete a substance that helps the movement of the sperm.
Sperm are formed in the seminiferous tubules by a process of cell division of the epithelial cells lining the walls of the tubules. New sperm are formed almost continuously during the sexual cycle of the male, and the number is very great.
The male discharge, called semen, consists of sperm, of which there may be 300,000,000 in a single ejaculation. The fluid secretions of the other accessory glands form an alkaline medium, so that the sperm are not killed by the acid reaction of the urethra into which the semen is emptied. The semen is propelled through the seminiferous tubules and vasa deferentia by means of cilia, which line the lumen of the ducts, and by the muscular contraction of the walls of the vas deferens.
The urethra passes through the penis, which is the male copulatory organ. The penis con...