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The male reproductive system consists of those structures in the male body designed to create life. The reproductive system includes the two testes, a network of ducts, the seminal vesicles, the prostate gland, and the penis.

The testes are two oval glands located in the scrotum (the pouch of skin that hangs behind the penis). They produce the male sex hormone testosterone and sperm (male reproductive cells). Sex hormones control the secondary male sex characteristics (such as growth of the penis and of body hair, voice change, and increased muscle mass), which begin to appear at puberty.

The testes discharge sperm into the epididymis, the first structure in the duct system. Other passageways include the two vasa deferentia (the plural of vas deferens), the ejaculatory duct, and the urethra (the tube that connects the bladder to the outside of the body).

The epididymis runs along the top and side of each testis. Inside the epididymis are several ducts that conduct sperm from the testis into the vas deferens. The vas deferens loops up into the body before descending into a duct in the seminal vesicle. This duct joins the ejaculatory duct, which extends through the prostate gland, and enters the upper segment of the urethra. At different times, the urethra functions as a passageway for urine and for sperm.

As sperm travel through the duct system, they combine with fluids from the seminal vesicles, the prostate gland, and the urethra to form semen. The two seminal vesicles, which lie near the underside of the urinary bladder, discharge a thick, sticky fluid. The prostate gland is a small, doughnut-shaped organ that completely surrounds the urethra. The prostate gland secretes an alkaline substance that makes up the major portion of seminal fluid. The sperm are protected from acid (present both in the male urethra and in the vagina) by the alkalinity of the prostatic secretions. Sperm are also capable of the greatest mobility when in a slightly alkaline medium. Proper prostate secretion is thus essential to effective sperm action.

The penis is the external organ that propels sperm into the female during sexual intercourse. During sexual excitement, the corpora cavernosa (large internal spaces within the penis) become filled with blood, making the penis rigid enough to enter the vagina (the entryway to the female reproductive tract). The semen, which is formed in the urethra, then travels out of the penis during ejaculation.

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