Hormones - Research Article from Macmillan Science Library: Animal Sciences

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The Two Major Hormone Groups

Hormones have been divided into two major groups that differ in their biochemical attributes, as well as in the mechanisms by which they affect the activity of target cells. These are steroid hormones and peptide hormones.

Steroid hormones are synthesized by endocrine glands in the gonads (ovaries and testes) and adrenal cortex. They are not stored but, rather, secreted into the circulatory system as soon as they are synthesized.

Steroid hormones are derived from cholesterol and are lipid soluble. Lipid solubility enables steroid hormones to cross cell membranes and enter directly into the cytoplasm. Once there, hormone molecules bind to cytoplasmic receptors, cross the nuclear membrane, and interact directly with DNA to affect cellular activity. Some well-known steroids are estrogen and testosterone.

Peptide hormones, on the other hand, are proteins and composed of amino acids. Peptide hormones are water soluble and range greatly in...

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This section contains 1,111 words
(approx. 4 pages at 300 words per page)
Buy the Hormones Encyclopedia Article
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Macmillan Science Library: Animal Sciences
Hormones from Macmillan Science Library: Animal Sciences. Copyright © 2001-2006 by Macmillan Reference USA, an imprint of the Gale Group. All rights reserved.
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