Hormone secretion is regulated by feedback mechanisms in order to maintain correct levels of substances in the blood. For example, a drop in the calcium level in the bloodstream stimulates an increase in the secretion of parathyroid hormone (PTH), which acts on various parts of the body to raise calcium levels. When calcium reaches the normal level, PTH secretion decreases.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.
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