The term hormone is derived from a Greek word meaning “to stir up.” Hormones act as chemical messengers in creating a communication chain that links the body systems together, thus controlling and integrating the functions of the body.
The endocrine glands are coordinated on the principle of negative feedback in which the rise or fall of one hormone can trigger an increase or decrease of another. For example, increased adrenocorticotropic hormone (ACTH) causes the adrenals to release more cortisol, which raises blood sugar levels. This in turn causes ACTH levels to decrease. Other substances in the bloodstream also affect hormone secretion. The amount of calcium in the blood, for example, regulates the release of parathormone (PTH) from the parathyroid glands, and the amount of sugar in the blood regulates insulin release.
Given the complex interaction of the endocrine glands, a disorder of one gland often affects other glands and the entire functioning of the body. Diabetes mellitus, for example, is the result of insulin deficiency, which causes high levels of blood sugar. Water is not properly processed by the kidneys when insulin is deficient, so frequent urination causes dehydration and excessive thirst. In addition, weight loss from the breakdown of fat stores causes excessive hunger. In contrast, a disorder of an exocrine gland is usually limited and seldom affects other glands or distant organs. An exception is cystic fibrosis, a genetic disorder that occurs in one out of every 2,000 births among Caucasians in the United States. In this disorder, the exocrine glands lining the pancreas and lungs produce thick mucous secretions that obstruct the glands and interfere with normal functioning of these organs.
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