Figure 1.

Hypotension-induced activation of the renin-angiotensin-aldosterone system. As blood pressure drops, juxtaglomerular cells receive signals from macula densa cells and the sympathetic nervous system and secrete renin into the circulation. Renin hydrolyzes liver-synthesized angiotensinogen into inactive ANG I. ANG I is converted to active ANG II by ACE. ANG II stimulates glomerulosa cells in the adrenal cortex to secrete aldosterone and the anterior pituitary gland in the brain to secrete the ACTH, which also results in aldosterone production. High K⁺ concentration stimulates aldosterone secretion from glomerulosa cells. Aldosterone increases Na⁺ reabsorption, K⁺ and H⁺ secretion in ASDN leading to an increase in blood pressure. ANG I, angiotensin I; ANG II, angiotensin II; ACE, angiotensin-converting enzyme; ASDN, aldosterone-sensitive distal nephron.