Hormones

Hormones are chemical messenger compounds secreted by one cell and travel through the circulatory system to affect the activities of other cells in the body. Hormones are produced by various organs and tissues, but mainly by glands in the endocrine system. Although the total number of hormones is not known, each has a unique function and chemical formula.

Hormones can be divided into three groups based on chemical structure:

amino acid derivatives (epinephrine, norepinephrine, thyroid hormones, and the pineal hormone called nelatonin)
peptide hormones (the largest class of hormones – all hormones secreted by the hypothalamus, pituitary, heart, kidneys, thymus, digestive tract, and pancreas. Peptide hormones consist of amino acid chains ranging from the short chains of ADH and oxytocin to larger ones of GH and prolactin)
lipid derivatives covers two groups:
- steroid hormones (derived from cholesterol). Steroid hormones are released by the reproductive organs and the adrenal glands and are structurally similar to cholesterol.
- fatty acid-based hormones (includes prostaglandins) are derived from arachidonic acid. They coordinate cellular activities and affect such enzymatic processes as blood clotting. Prostaglandins are not glands. They are hormones produced from linoleic acid, an oemga-6 essential fatty acid. Prostaglandins have been found in semen, the kidneys, uterus, blood cells, joints, and other tissues. They control many reactions, including labour, menstruation, blood clotting, and immunity.

This page was updated in November 2005.