Key Concepts
Introduction
Adrenal disorders encompass a spectrum of conditions arising from dysfunction of the hypothalamic-pituitary-adrenal (HPA) axis, resulting in either cortisol excess (Cushing syndrome) or deficiency (adrenal insufficiency/Addison disease), with adrenal crisis representing the most acute and life-threatening manifestation. HPA Axis Physiology and Cortisol Regulation: The HPA axis operates through a hierarchical hormonal cascade with negative feedback regulation. The hypothalamus releases corticotropin-releasing hormone (CRH) in a pulsatile, circadian pattern (highest in early morning, lowest at midnight). CRH travels through the hypothalamic-hypophyseal portal system to the anterior pituitary, where it stimulates corticotroph cells to secrete adrenocorticotropic hormone (ACTH) via CRH receptor-1 (CRHR1) activation of the cAMP-PKA signaling pathway. ACTH is cleaved from its precursor pro-opiomelanocortin (POMC), along with beta-endorphin, melanocyte-stimulating hormone (MSH), and other peptides. ACTH enters the systemic circulation and binds to melanocortin-2 receptors (MC2R) on zona fasciculata cells of the adrenal cortex, activating cAMP-PKA signaling that stimulates cholesterol uptake (via StAR protein) and steroidogenic enzyme activity, producing cortisol. Cortisol exerts negative feedback at both the hypothalamus (suppressing CRH) and anterior pituitary (suppressing ACTH). This feedback loop maintains cortisol within a physiologic...