Hormones are the natural chemical messengers of our bodies.
Secreted into our bloodstream in carefully measured amounts by the endocrine glands, these chemicals then bind to special receptors in different parts of the body and thereby control and adjust many body functions. Thyroid hormone adjusts our metabolic rate, thereby affecting appetite, temperature, and even normal turnover of hair and skin. In the fetus, thyroid hormone strongly influences normal brain development. Infants born of mothers with low thyroid hormone levels almost always suffer from severe mental retardation. Estrogen, secreted primarily by the ovaries, influences the menstrual cycle, fertility, pregnancy, and crucial stages in infant development.