Chapter 33: Adrenal Gland & Stress Hormone Regulation

The text details the histological zonation of the adrenal cortex, describing how the zona glomerulosa synthesizes the mineralocorticoid aldosterone, while the zona fasciculata and zona reticularis are responsible for producing glucocorticoids like cortisol and adrenal androgens such as dehydroepiandrosterone (DHEA). A significant portion of the chapter explains the biochemistry of steroidogenesis, where cholesterol—derived primarily from low-density lipoproteins (LDL) or synthesized de novo from acetate—is converted into pregnenolone by the cytochrome P450 enzyme CYP11A1 within the mitochondria. The summary explores the regulation of these pathways, noting that adrenocorticotropic hormone (ACTH) drives glucocorticoid and androgen synthesis via the cAMP signaling pathway, whereas aldosterone secretion is primarily regulated by angiotensin II and extracellular potassium levels through calcium-dependent mechanisms. Key metabolic functions of glucocorticoids are highlighted, particularly their role in adapting the body to fasting by promoting gluconeogenesis, stimulating lipolysis, and inhibiting protein synthesis to maintain blood glucose levels. Furthermore, the text examines the anti-inflammatory and immunosuppressive properties of glucocorticoids, as well as their vital role in the stress response. The discussion extends to the adrenal medulla, which functions as a modified sympathetic ganglion to secrete epinephrine and norepinephrine, hormones that mediate the fight-or-flight response and defend against hypoglycemia by stimulating glycogenolysis and lipolysis. Clinical correlations are integrated throughout, explaining pathologies such as Cushing disease caused by glucocorticoid excess, Addison disease resulting from primary adrenal insufficiency, and congenital adrenal hyperplasia arising from genetic defects in steroidogenic enzymes like 21-hydroxylase. Finally, the chapter touches upon the role of the enzyme 11beta-hydroxysteroid dehydrogenase in tissue-specific cortisol metabolism and its potential link to obesity and metabolic syndrome.