Ovaries And Testes

Like the other endocrine glands, which usually go unnoticed unless they malfunction, the testes in men and the ovaries in women play a crucial role. Their pervasive influence is particularly evident during the teenage years, when sex hormones surge and sexual maturation takes place. At no other time, except perhaps in the first few years of life (and most of us do not remember much of that), do our bodies undergo such dramatic and rapid changes. Sex hormones affect much more than physical appearance, and their control extends even beyond the physiological processes of sexual maturation and reproduction. They also hold sway over emotions and attitudes by opening up a whole spectrum of desire.

Sexual development begins at the instant of conception. The fertilized egg carries within it every piece of genetic information it will ever need to produce every type of cell for a lifetime. Thus, from the very beginning, it is determined whether an embryo will mature into a male or female. Sex organs begin to show up very early in fetal development. Testicles begin to emerge in about the seventh week, and ovaries start to form in the 16th week. Sex hormone levels in the developing fetus are high. These hormones directly influence the fetal development of the sex glands.

Some medical experts believe that these early hormones affect the developing brain and contribute to behavioral differences between men and women. There are others, though, experts or not, who argue vehemently against this. These people believe that social factors, not biological ones, are solely responsible for the differences between how men and women act.

Once a baby is born, its sex hormone production drastically reduces. No one is sure what function sex hormones serve in children. Although the testes and ovaries of children are capable of manufacturing and secreting hormones, the pituitary gland has not yet provided the activating signals.

Gonads and ovaries

The male gonads, or testes, have a unique location. They lie suspended between the thighs in a sac called the scrotum. The testes are situated outside the body because they need a lower temperature to produce viable sperm. These two egg-shaped organs are about two inches long and together weigh less than an ounce. They have two main components. The seminiferous tubules are long, narrow, curling tubes in which sperm cells are formed. These tubes are tightly packed into the testes and compose about 95% of the glands. The little spaces between the tubes hold Leydig's cells. These cells produce nearly all of the androgens, including testosterone, the major androgen hormone secreted by the testes.

Ovaries are the female gonads. One sits on each side of the uterus and is attached to it by ligaments. They are oval-shaped and measure about an inch and a half in length. Ovaries vary in weight in different stages of a female's life but weigh the most during the years that she is fertile. The ovaries produce the hormones estrogen, progesterone, and relaxin. At birth, the ovaries of a female already contain all of the egg-forming cells, or follicles, she will ever produce. It is thought that females begin with a supply of 2 million of these follicles. Only one is used each month in the development of a mature egg.

Like the hormones of the adrenal cortex, hormones of the sex glands are steroids. Although they share a similar carbohydrate origin, they are crucially different in final form and function. Each gland contains particular enzymes that account for the synthesis of specific steroids. The manufacture and secretion of the gonads is under the control of the hypothalamus and the pituitary.

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