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High-Yield Terms

  • Endocrine glands: secrete chemicals or hormones into the circulation

  • Exocrine glands: excretes chemicals or hormones via ducts

  • Paracrine: refers to any substance secreted by one cell which acts on cells next to or in close proximity to the source

  • Autocrine: refers to any substance secreted by one cell which acts on the secreting cell itself

  • Cretinism: a condition of severely stunted physical and mental growth due to untreated congenital deficiency of thyroid hormones

  • Thyrotoxicosis: the condition resulting from hyperthyroidism leading to excess production and release of thyroid hormoness

Basics of Peptide Hormone Structure and Function

The integration of metabolic and hemostatic functions is carried out by the nervous system, the immune system, and the endocrine system. The endocrine system is composed of a number of tissues that secrete their products, endocrine hormones, into the circulatory system; from there they are disseminated throughout the body, regulating the function of distant tissues and maintaining homeostasis. In a separate but related system, exocrine tissues secrete their products into ducts and then to the outside of the body or to the intestinal tract. Classically, endocrine hormones are considered to be derived from amino acids, peptides (Table 49-1), or sterols (Chapter 50) and to act at sites distant from their tissue of origin. However, some secreted substances act at a distance (classical endocrines), close to the cells that secrete them (paracrine), or directly on the cell that secreted them (autocrine).

TABLE 49-1:Major Peptide Hormones

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