Academic journal article Alcohol Health & Research World

The Endocrine System: An Overview

Academic journal article Alcohol Health & Research World

The Endocrine System: An Overview

Article excerpt

A plethora of hormones regulate many of the body's functions, including growth and development, metabolism, electrolyte balances, and reproduction. Numerous glands throughout the body produce hormones. The hypothalamus produces several releasing and inhibiting hormones that act on the pituitary gland, stimulating the release of pituitary hormones. Of the pituitary hormones, several act on other glands located in various regions of the body, whereas other pituitary hormones directly affect their target organs. Other hormone-producing glands throughout the body include the adrenal glands, which primarily produce cortisol; the gonads (i.e., ovaries and testes), which produce sex hormones; the thyroid, which produces thyroid hormone; the parathyroid, which produces parathyroid hormone; and the pancreas, which produces insulin and glucagon. Many of these hormones are part of regulatory hormonal cascades involving a hypothalamic hormone, one or more pituitary hormones, and one or more target gland hormones. KEY WORDS: endocrine function; hormones; hypothalamus; pituitary gland; gonad function; thyroid; parathyroid; pancreas; biochemical mechanism; biological feedback; biological regulation; hypothalamus-pituitary axis; pituitary-adrenal axis; pituitary-thyroid axis; literature review

For the body to function properly, its various parts and organs must communicate with each other to ensure that a constant internal environment (i.e., homeostasis) is maintained. For example, neither the body temperature nor the levels of salts and minerals (i.e., electrolytes) in the blood must fluctuate beyond preset limits. Communication among various regions of the body also is essential for enabling the organism to respond appropriately to any changes in the internal and external environments. Two systems help ensure communication: the nervous system and the hormonal (i.e., neuroendocrine) system. The nervous system generally allows rapid transmission (i.e., within fractions of seconds) of information between different body regions. Conversely, hormonal communication, which relies on the production and release of hormones from various glands and on the transport of those hormones via the bloodstream, is better suited for situations that require more widespread and longer lasting regulatory actions. Thus, the two communication systems complement each other. In addition, both systems interact: Stimuli from the nervous system can influence the release of certain hormones and vice versa.

Generally speaking, hormones control the growth, development, and metabolism of the body; the electrolyte composition of bodily fluids; and reproduction. This article provides an overview of the hormone systems involved in those regulatory processes. The article first summarizes some of the basic characteristics of hormonemediated communication within the body, then reviews the various glands involved in those processes and the major hormones they produce. For more in-depth information on those hormones, the reader should consult endocrinology textbooks (e.g., Constanti et al. 1998; Wilson et al. 1998). Finally, the article presents various endocrine systems in which hormones produced in several organs cooperate to achieve the desired regulatory effects. The discussions focus primarily on the system responses in normal, healthy people. For information regarding alcohol's effects on some of the hormone systems, the reader is referred to subsequent articles in this issue of Alcohol Health & Research World.

WHAT ARE HORMONES?

Hormones are molecules that are produced by endocrine glands, including the hypothalamus, pituitary gland, adrenal glands, gonads, (i.e., testes and ovaries), thyroid gland, parathyroid glands, and pancreas (see figure 1). The term "endocrine" implies that in response to specific stimuli, the products of those glands are released into the bloodstream.l The hormones then are carried via the blood to their target cells. …

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