ABSTRACT
ALDOSTERONE PHYSIOLOGY The renin angiotensin aldosterone system (RAAS) is an adaptation to maintain adequate salt and water balance and circulatory homeostasis during periods of deprivation. This sensitive regulation involves various sensors and has complex feedback mechanisms. In response to decreased renal perfusion, renin is secreted by the juxtaglomerular cells lining the renal afferent arterioles. Renin cleaves circulating angiotensinogen, forming angiotensin I, which is then further cleaved by angiotensin-converting enzyme (ACE) into the biologically active form angiotensin II. Angiotensin II acts to maintain circulatory homeostasis by potent renal and systemic vasoconstriction, proximal tubule sodium reabsorption, and signaling the adrenal cortex to secrete the steroid hormone, aldosterone. Aldosterone promotes the reabsorption of sodium, in exchange for potassium, in the distal nephron as well as the colon, salivary, and sweat glands. Aldosterone is also secreted directly in response to elevated potassium, causes potassium and magnesium urinary loss, therefore playing an integral role in electrolyte homeostasis. Because of its physiologic role in the regulation of sodium and potassium, it has been termed a mineralocorticoid (1).
