Each of these hormones targets specific receptors in the body to stimulate specific glands and tissues in the body. The thyroid gland, ovaries, testes, mammary glands, and the cortex of the adrenal glands are all stimulated by the hormones of the anterior pituitary, resulting in the pituitary gland historically being known as the “master gland” for its control of the endocrine system. More modern studies now show that, while still very important, the anterior pituitary is subservient to the control of the hormones of the hypothalamus. Releasing hormones from the hypothalamus, such as thyrotropin-releasing hormone (TRH) and gonadotropic-releasing hormone (GnRH), stimulate the anterior pituitary to release TSH, FSH, and LH. Inhibiting hormones, such as growth hormone-inhibiting hormone (GHIH), prevent the secretion of hormones hGH and TSH.
The levels of hormones in the body can be regulated by several factors. The nervous system can control hormone levels through the action of the hypothalamus and its releasing and inhibiting hormones. For example, TRH produced by the hypothalamus stimulates the anterior pituitary to produce TSH. Tropic hormones provide another level of control for the release of hormones. For example, TSH is a tropic hormone that stimulates the thyroid gland to produce T3 and T4. Nutrition can also control the levels of hormones in the body. For example, the thyroid hormones T3 and T4 require 3 or 4 iodine atoms, respectively, to be produced. In people lacking iodine in their diet, they will fail to produce sufficient levels of thyroid hormones to maintain a healthy metabolic rate. Finally, the number of receptors present in cells can be varied by cells in response to hormones. Cells that are exposed to high levels of hormones for extended periods of time can begin to reduce the number of receptors that they produce, leading to reduced hormonal control of the cell.
Endocrinologists-in-training then spend two or three more years learning how to diagnose and treat hormone conditions. Overall, an endocrinologist's training will take more than 10 years after the undergraduate degree. They are certified by the American Board of Internal Medicine. Endocrinologists typically specialize in one or two areas of endocrinology, such as diabetes or infertility. These specialists treat patients with fertility issues and also assess and treat patients with health concerns surrounding menstruation and menopause, Loh noted.