Anatomy & Physiology I and II

Anatomy & Physiology Study Guide

©2018 Achieve Test Prep Page 217 of 367 17.14 Chapter Seventeen Review Homeostasis is preserved through intercellular communication: • In general, the nervous system performs short-term “crisis management,” whereas the endocrine system regulates longer-term, ongoing metabolic processes. • Paracrine communication involves the utilization of chemical signals to transfer data from cell to cell within a single tissue. • Endocrine communication occurs when chemicals, also known as hormones, are sent into circulation by endocrine cells. The hormones change the metabolic activities of many tissues and organs simultaneously by modifying the activities of target cells. The endocrine system regulates physiological processes through the binding of hormones to receptors: • The endocrine system includes all the cells and endocrine tissues of the body that produce hormones or paracrine factors. • Hormones can be categorized into three groups: amino acid derivatives; peptide hormones; and lipid derivatives, including steroid hormones and eicosanoids. • Hormones may circulate freely or bound to transport proteins. Free hormones are rapidly removed from the bloodstream. • Receptors for catecholamines, peptide hormones, and eicosanoids are in the plasma membranes of target cells. Thyroid and steroid hormones cross the plasma membrane and bind to receptors in the cytoplasm or nucleus, activating or inactivating specific genes. • Endocrine reflexes are the counterparts of neural reflexes. • The hypothalamus regulates the actions of the nervous and endocrine systems by secreting regulatory hormones, which control the activities of endocrine cells in the adenohypophysis; acting as an endocrine organ by releasing hormones into the bloodstream at the neurohypophysis and exerting direct neural control over the endocrine cells of the suprarenal medullae. The bilobed pituitary gland is an endocrine gland that releases nine peptide hormones: • The pituitary gland, or hypophysis, releases nine important peptide hormones; all bind to membrane receptors and use cyclic-AMP as a second messenger. • The adenohypophysis, or anterior lobe, of the pituitary gland, is subdivided into three pars: pars distalis, pars intermedia, and pars tuberalis. • At the median eminence of the hypothalamus, neurons release regulatory factors, either releasing hormones, RH, or inhibiting hormones, IH, into the nearby interstitial fluids through fenestrated capillaries. • The hypophyseal portal system ensures that these regulatory factors reach the intended target cells before they enter the general circulation. • Thyroid-stimulating hormone (TSH) triggers the release of thyroid hormones. Thyrotropin- releasing hormone (TRH) promotes the secretion of TSH.