You probably know that the kidneys play an important role in maintaining blood pressure within the normal range. You might also know that they do this by regulating blood volume and the degree of arterial contraction or dilation (the systemic vascular resistance). But do you know how the kidneys do this? The answer is the kidneys accomplish this primarily through a set of hormones and enzymes known together as the renin-angiotensin-aldosterone system (RAAS). In this brick, we will discuss the components, functions, and regulation of the RAAS.

Renin is an enzyme released by the kidneys that ultimately causes the formation of the hormone angiotensin II (Ang II) in the body—which in turn stimulates the release of the hormone aldosterone from the adrenal cortex. Ang II and aldosterone act in a number of ways to increase blood volume and blood pressure.

RAAS acts to increase sodium reabsorption in the kidney, increase vascular tone, and even stimulate antidiuretic hormone (ADH) to reabsorb more water: all of these defend our extracellular volume and blood pressure. RAAS is therefore a critical system for keeping us upright!

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from our Musculoskeletal, Skin, and Connective Tissue collection, which is available for free.

Learn more about Rx Bricks by signing up for a free USMLE-Rx account: www.usmle-rx.com

You will get 5 days of full access to our Rx360+ program, including nearly 800 Rx Bricks.  After the 5-day period, you will still be able to access over 150 free bricks, including the entire collections for General Microbiology and Cellular and Molecular Biology.