Pathophysiology
Clinical meaning
the clinician manages complex fluid and electrolyte disorders through advanced understanding of the renin-angiotensin-aldosterone system (RAAS), antidiuretic hormone (ADH) physiology, natriuretic peptides, and renal tubular function. RAAS activation begins when juxtaglomerular cells detect decreased renal perfusion pressure, releasing renin that converts angiotensinogen to angiotensin I, then to angiotensin II by ACE. Angiotensin II causes systemic vasoconstriction, stimulates aldosterone secretion promoting sodium and water reabsorption via ENaC channels, and stimulates ADH release. The clinician interprets complex acid-base disorders using the systematic approach: identify the primary disorder, calculate expected compensation, calculate the anion gap, and calculate the delta-delta ratio to identify concurrent metabolic disorders.