Chapter 23: Endocrine Control of Growth and Metabolism

Endocrine Control of Growth and Metabolism physiological review provides an in-depth analysis of the endocrine mechanisms regulating growth and metabolism, focusing on the adrenal, thyroid, and parathyroid systems,. The chapter begins by detailing the adrenal cortex and its synthesis of steroid hormones from cholesterol, specifically distinguishing between mineralocorticoids like aldosterone, sex steroids, and the vital glucocorticoid cortisol,. It thoroughly examines the hypothalamic-pituitary-adrenal (HPA) pathway, explaining how corticotropin-releasing hormone (CRH) and adrenocorticotropic hormone (ACTH) control cortisol secretion through negative feedback loops, and describes cortisol's catabolic role in promoting gluconeogenesis, skeletal muscle breakdown, and lipolysis during stress,. Significant attention is given to endocrine pathologies, contrasting the physiological effects of hypercortisolism (Cushing's syndrome) with hypocortisolism (Addison's disease), as well as the related physiology of POMC peptides and melanocortins,. The text then shifts to thyroid physiology, outlining the synthesis of T3 and T4 from tyrosine and iodine within the thyroid follicles and their regulation by TSH to control basal metabolic rate and thermogenesis,. Disorders such as Graves' disease, myxedema, and goiter are analyzed in the context of feedback dysfunction,. The summary further explores somatic growth regulation, highlighting the anabolic interplay between growth hormone (GH) and insulin-like growth factors (IGFs) in tissue hypertrophy and hyperplasia,. Finally, the chapter elucidates calcium homeostasis and bone physiology, detailing the remodeling cycle controlled by osteoblasts and osteoclasts via the RANKL and osteoprotegerin (OPG) system. It concludes by explaining the regulatory triad of parathyroid hormone (PTH), calcitriol (Vitamin D3), and calcitonin in maintaining plasma calcium levels to prevent conditions like hypocalcemic tetany and osteoporosis.