Endocrinology is a sub-discipline of medicine that specializes in hormones. Medterms defines the specialty as “The study of hormones, their receptors, the intracellular signaling pathways they invoke, and the diseases and conditions associated with them.” The field overlaps with reproductive medicine and the study of metabolic disorders, such as diabetes.
Hormones are signaling molecules secreted into the blood stream by glands, which make up the endocrine system. The human glands include (see a diagram on ehow) the thyroid, pituitary, hypothalamus, thymus, adrenals, pineal, islets of Langerhans (pancreas), ovaries, and testes. A number of physiological processes are based on these signaling pathways, including menstruation, blood pressure, glucose metabolism, development of sex characteristics, bone growth, and mood. The other system of the human body to control physiological processes is the nervous system. Neuroendocrinology specializes in the overlap between neurology and endocrinology.
Hormone receptors are proteins that specifically bind certain hormones. Examples of these pairings include estrogen and estrogen receptor, insulin and insulin receptor, and thyroid hormone and thyroid hormone receptors. The receptor binding can result in a signaling cascade within cells that affects gene transcription, sometimes of other hormones. The endocrine receptors that work in this way are nuclear hormone receptors. These receptors can then bind to specific DNA response elements to affect gene transcription. Other receptors are steroid hormone receptors, which bind steroid hormones such as thyroid hormone. A more detailed explanation of receptor function is presented by Kimball in his online biology textbook. Some hormones, such as insulin, act on the cell membrane to increase cell permeability to other substances, such as glucose.
Endocrine defects can occur as hyper-secretion (too much hormone), hypo-secretion (too little hormone), or receptor defects. In addition, the disorders treated by endocrinologists, according to Medline, can be pediatric or adult, and acute or chronic, depending on the reason for the altered hormones. For example, diabetes occurs as two chronic types. One type (type I) presents in childhood and remains throughout life because the pancreas does not produce enough of the hormone insulin. The other type (type II) presents later in life after the pancreas has previously secreted insulin normally. Type II diabetics may either not produce enough insulin because of autoimmune damage to the pancreas, or their insulin receptors do not function properly. An acute form of diabetes, a type that only lasts a certain period of time is gestational diabetes. This form occurs during pregnancy but the insulin response returns to normal after pregnancy.
The Society for Endocrinology offers information about the various pathways and disorders studied and treated in the field of endocrinology.