Hormones

The word hormone is derived from a Greek word meaning “to arouse to activity.” Endocrinologists are physicians who specialize in the study of the endocrine system, which generates hormones. This system was first identified by French physician Claude Bernard (1813–78) in the mid-19th century. The [Page 863]word endocrine is also Greek in origin and means “separated within,” which describes the actions by which hormonal activity is aroused in the cells of origin (autocrine) as well as in the surrounding cells (paracrine). Once hormones are secreted, they enter into the blood stream to perform specific functions, thereby keeping the body in working order as they interact with the brain, heart, liver, kidneys, digestive system, nervous system, immune system, and other parts and systems of the body. As they perform their assigned functions, hormones regulate the rate of chemical reactions in specific cells and influence the way in which substances in the body are transported through cell membranes. Once hormones perform their specific functions, they are eliminated through the kidneys.

Hormones also play a major role in growth and development. Malfunctions of growth hormones may lead to either dwarfism or gigantism. During conception, hormones influence the formation of sex organs. After birth, hormone levels decline. During puberty, which generally begins in industrialized nations between the ages of 12 and 14 years, hormone levels rise rapidly. Puberty may be delayed in poorer countries as a result of poor nutrition. If malfunctions occur in the production of sex hormones, individuals may not develop the secondary sex characteristics that lead to male and female characteristics in adulthood. During puberty, females normally start to menstruate as their bodies begin producing eggs in preparation for motherhood. Subsequently, fluctuating hormonal levels may result in pre-menstrual syndrome (PMS), which is associated with a variety of symptoms such as pain, bloating, and wide mood swings. Delayed or absent menstruation or abnormal menstrual pain are indicative of possible problems.

Male hormones released during puberty result in the appearance of facial and body hair, deepened voices, elongation of the long bones of limbs, and increased aggression and libido. Male and female hormones during puberty are also responsible for teenage acne and for the infamous moodiness of teenagers. Because hormones exercise some neural controls over emotions, they also determine how humans of all ages deal with stress and emotions such as aggression and fear.

The major female hormone, estrogen, and the major male hormone, testosterone, activate the sex drive and control fertility, ensuring that the human race will survive through procreation. Once a female becomes pregnant, estrogen and progesterone prepare her body for motherhood. When she reaches the end of her childbearing years, levels of “female” hormones drop, and a woman enters menopause. In one percent of females, premature ovarian failure occurs when a woman under the age of 40 stops producing estrogen and enters menopause. The physical protections that estrogen provides have been well documented, and hormone replacement therapy (HRT) has been widely used to offset the loss of estrogen during and after menopause. However, a number of studies have linked HRT to cancer, particularly breast cancer, and many women have sought alternative methods of dealing with estrogen loss. In males, some studies have revealed a link between high testosterone levels, which may be associated with high dietary fat intake, and prostate cancer. However, the exact causes of such cancers are unknown.

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