Figure 121

Renin-angiotensin system. The renin-angio-tensin system serves as one of the most powerful regulators of arterial pressure and sodium balance. In response to various stimuli that compromise blood volume, extracellular fluid (ECF) volume, or arterial pressure—or those associated with stress and trauma—three major mechanisms are activated. These mechanisms stimulate renin release by the cells of the juxtaglomerular apparatus that act on angiotensinogen to form angiotensin I. Angiotensinogen is an <2 globulin formed primarily in the liver and to a lesser extent by the kidney. Angio-tensin I is a decapeptide that is rapidly converted by angiotensin-converting enzyme (ACE) and to a lesser extent by chymase (in the heart) to angiotensin II, an octapeptide. Recent studies have indicated that other angiotensin metabolites such as angiotensin (2-8), angiotensin (1-7), and angiotensin (3-8) have biologic actions.

Adrenal cortex

Angiotensin II and/or active metabolites

Adrenal cortex

Maintain or increase extracellular fluid volume

Central nervous system t Proximal and distal sodium + water t Reabsorption by intestine t Proximal and distal sodium + water t Reabsorption by intestine

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