Mechanisms of Hormonal Regulation
Endocrine glands respond to specific signals by synthesizing and releasing hormones into circulation, which then trigger intracellular responses. Although a wide variety of hormones function in the body, they share certain general characteristics:
Hormones have specific rates and rhythms of secretion.
The three basic secretion patterns are:(a) circadian or diurnal patterns, (b) pulsatile and cyclic patterns, and (c) patterns that depend on levels of circulating substrates (for example, calcium, sodium, potassium, or the hormones themselves).
Hormones operate within feedback systems, either positive or negative, to maintain an optimal internal environment.
Hormones affect only cells with appropriate receptors and then act on those cells to initiate specific cell functions or activities.
Steroid hormones are either excreted directly by the kidneys or metabolized (conjugated) by the liver, which inactivates them and renders the hormone more water soluble for renal excretion. Peptide hormones are catabolized by circulating enzymes and eliminated in the feces or urine.