Concepts of Human Anatomy & Physiology   5/e   Van De Graaff/Fox
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I. Endocrine Glands and Hormones

Concept: Hormones are regulatory molecules secreted into the blood by endocrine glands. Chemical categories of hormones include steroids, amines, polypeptides, and glycoproteins. Interactions occur between the various hormones to produce effects that may be synergistic, permissive, or antagonistic.

II. Mechanisms of Hormone Action

Concept: Each hormone exerts its characteristic effects on target organs by acting on the cells of these organs. Hormones of the same chemical class have similar mechanisms of action. Lipid-soluble hormones pass through the target cell membrane, bind to the intracellular receptor proteins, and act directly within the target cell. Polar hormones do not enter the target cells, but instead bind to receptors on the cell membrane. This results in the activation of intracellular second-messenger systems that mediate the actions of the hormone.

III. Pituitary Gland

Concept: The pituitary includes the anterior pituitary and posterior pituitary. The posterior pituitary stores and releases hormones that are actually produced by the hypothalamus, whereas the anterior pituitary produces and secretes its own hormones. The anterior pituitary, however, is regulated by hormones secreted by the hypothalamus, as well as by feedback from the target gland hormones.

IV. Adrenal Glands

Concept: The adrenal cortex and adrenal medulla are structurally and functionally different. The adrenal medulla secretes catecholamine hormones, which complement the sympathetic nervous system in the "fight-or-flight" reaction. The adrenal cortex secretes steroid hormones that participate in the regulation of mineral and energy balance.

V. Thyroid and Parathyroid Glands

Concept: The thyroid gland secretes thyroxine (T4) and triiodothyronine (T3), which are needed for proper growth and development and which are primarily responsible for determining the basal metabolic rate (BMA). The parathyroid glands secrete parathyroid hormone, which helps to raise the blood Ca2+ concentration.

VI. Pancreas and Other Endocrine Glands

Concept: The pancreatic islets secrete two hormones, insulin and glucagon. Insulin promotes the lowering of blood glucose and the storage of energy in the form of glycogen and fat. Glucagon has antagonistic effects which act to raise the blood glucose concentration. Additionally, many other organs secrete hormones that help to regulate digestion, metabolism, growth, immune function, and reproduction.

VII. Autocrine and Paracrine Regulation

Concept: Many regulatory molecules produced throughout the body act within the organs that produce them. These molecules may regulate different cells within one tissue, or they may be produced within one tissue and regulate a different tissue within the same organ.

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