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The Endocrine System


A hormone is a chemical that is produced by the body and has a specific regulatory effect on a target cell or organ. Classic endocrinology was concerned with the functions of anatomically defined glands such as the thyroid gland or the pituitary gland. It is now recognized that almost every organ secretes hormones and that endocrine cells may be dispersed throughout the body (e.g., in the gut mucosa). The more recent study of endocrinology encompasses all processes concerned with the physiology of hormones. Certain diseases commonly encountered in general medical practice, such as diabetes mellitus or thyroid disorders, are caused by a deficiency or an excess of specific hormones. Many other common diseases not directly caused by endocrine dysfunction have prominent endocrine components, including cancer and atherosclerosis. Table 8-1 summarizes the hormones produced by the major endocrine organs.

Table 8-1Summary of Hormones Produced by the Major Endocrine Organs

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