Hormonal control and the endocrine system: achieving homeostasis

Endocrine tissue is also present in many organs that are not normally associated with the endocrine system. For example, the hormone erythropoietin is secreted by endocrine cells in the kidney and affects the production of red blood cells by the bone marrow. Hormones such as gastrin are produced by the cells of the stomach and circulate locally to affect the muscle and exocrine glands of the intestinal tract. Hormones are released into the bloodstream where they travel through the body but only the cells that that have receptors for that particular hormone (target cells) will be affected. The receptors have a particular configuration that fits the hormone; this is the hormone binding site. The production of hormones is controlled, so that, in the healthy state, there is no overor underproduction. This regulation is often a ‘self control’ mechanism; if the level of a hormone is increasing, the body will detect this and inhibit further production. The reverse situation is also true: if the level of a hormone is becoming too low, more will then be produced. The same type of control is true for nonhormone systems such as blood glucose or blood calcium. For example, the body detects a rising level of blood glucose, and mechanisms are put in place to ensure the level does not rise above the upper limit of the normal range. It is outside the scope of this article to describe all the functions of the hormones discussed, or all their interactions, but it should be borne in mind that hormones interact and have an effect on each other. AbstrAct The endocrine system is one of the primary control mechanisms in the body. This article defines some of the terminology used in describing the endocrine system and describes some examples of hormone systems and how drugs may be used to help manage these.