The principles of hormone action include fundamental concepts such as hormone biosynthesis and secretion, feedback regulation, hormone-receptor binding, and initiation of intracellular signaling. These principles are broadly applicable and can be applied to the physiology of other subspecialties.
HORMONE BIOSYNTHESIS AND SECRETIONHormones can be divided into five major classes: (1) amino acid derivatives such as dopamine, catecholamines, and thyroid hormone; (2) small neuropeptides such as GnRH, TRH, somatostatin, and vasopressin; (3) large proteins such as insulin, LH, and PTH produced by classic endocrine glands; (4) steroid hormones such as cortisol and estrogen that are synthesized from cholesterol-based precursors; and (5) vitamin derivatives such as retinoids (vitamin A) and vitamin D. As a rule, amino acid derivatives and peptide hormones interact with cell-surface membrane receptors. Steroids, thyroid hormones, vitamin D, and retinoids are lipid …
