Human Reproductive System

Male and female human reproductive system develop from a similar set of embryological structures and many structural and functional parallels exist. Individual difference occur in the shape and structure of genitals, but without interfering with reproductive or sexual function. Also, the sexual anatomy of a young child differs from that of a mature adult, and in turn, adult sexual anatomy alters in the later years of life.

Male Reproductive System
The male reproductive system basically is designed to produce and transport sperm cells. At the same time, the male genitals play an obvious role in sexual behavior, because reproduction cannot take place unless sperm cells are deposited in the female reproductive system. The major organs of the male reproductive system are the testes (testicles), the prostate, the seminal vesicles, the vast deference, the epidermis, and the penis.

Testes
The testes, which are contained in a pouch of skin called the scrotum, are located outside of the body because they require a lower temperature than the rest of the body in order to accomplish one of their main functions, the reproduction of sperm cells (spermatogenesis). Each of the testes are suspended from the body and held in place by a spermatic cord, the skin of the scrotum contains numerous sweat glands that assist in the cooling process.

Spermatogenesis
Within the scrotum, each testis is contained by a thick protective capsule, within which is a network of tightly coiled tubes called the seminiferous tubules. Sperm production fully occurs usually by the age of 16, even though it can begin before a boy reaches puberty. The male continuous to produce sperm throughout his life but with a marked slowing of the process in the later years. A man often is able to father children when he is into his seventies or eighties, but the peak of his fertility is typically earlier in the life cycle. The testes also produce the male hormones, or androgen, in large cells called the interstitial cells of leydig. Like the production of sperm, the manufacture and secretion of these hormones begins about the time of puberty and continues throughout life. The hormone circulate throughout the body, affecting various organs.

Pathway of the Sperm
Sperm produced in the seminiferous tubules move through the testes into another system of coiled ducts called the epididymis. The sperm remain here and continue to mature for about 2 weeks and then pass into a duct called the vas deferens. The male sterilization procedure, or vasectomy, involves cutting the vas deferens so that the sperm cannot travel from the testes to the penis.

Seminal Fluids
Before the sperm cells reach the penis, they travel through the seminal vesicles and the prostate and Cowper's glands. The major function of these internal organs is to produce fluids that will provide the sperm with a nourshing and balanced environment. Only a very small proportion of the male ejaculate is made up of sperm cells, the remainder consist of the seminal fluids secreted by these internal organs. Thus a male who undergoes vasectomy will continue to ejaculate about the same volume of fluid as a fertile male. Seminal fluid are not absolutely necessary for a man to be fertile, but these fluids allow the sperm to live longer within the vagina's acidic environment.

The Penis
In the final phase of their journey, the sperm cells pass through the urethral duct, which runs through the center of the penis. The penis contains a large number of arteries, veins, and small blood vessels as well as erectile tissue, the last of which consists of three hollow, sponge-like cylinders of tissue. When a male has an erection, these spongy tissues fill with blood and become firm. Unlike that of a number of other mammals, for instance, the whale, no bones are located within the human penis. Erection is caused solely by the relaxation of the blood vessels within the penis. Thus when a man is under emotional or physical stress, he may experience some difficulty achieving a firm erection because the blood vessels may not relax sufficiently.

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