Renin-angiotensin-aldosterone system

Renin-Angiotensin-Aldosterone System

Latin	Systema reninum-angiotensinum-aldosteronum
System	Endocrine system

The Renin-Angiotensin-Aldosterone System (RAAS) is a critical hormone regulation system that controls blood pressure, fluid balance, and electrolyte levels in the body. It involves the production and regulation of several key substances, including renin, angiotensin II, and aldosterone.

Overview

The RAAS plays a central role in cardiovascular and renal function. It is activated when there is a decrease in blood volume or blood pressure, or when there is a decrease in sodium concentration in the kidneys. The system starts with the release of renin, an enzyme, from the juxtaglomerular cells in the kidneys.

Components

Renin

Renin is released into the bloodstream where it acts on a substrate called angiotensinogen, which is produced by the liver, converting it into angiotensin I.

Angiotensin I

Angiotensin I is a relatively inactive peptide that is converted into the potent vasoconstrictor angiotensin II by the enzyme angiotensin-converting enzyme (ACE), which is found in the lungs and other tissues.

Angiotensin II

Angiotensin II has multiple effects:

• It stimulates the contraction of blood vessels, increasing blood pressure.
• It stimulates the secretion of aldosterone from the adrenal cortex.
• It stimulates the reabsorption of sodium, and therefore water, in the kidneys, which increases blood volume and blood pressure.
• It stimulates the secretion of antidiuretic hormone (ADH), which also helps in water reabsorption by the kidneys.

Aldosterone

Aldosterone further increases blood volume and pressure by promoting sodium and water retention in the kidneys. It also causes the excretion of potassium.

Regulation

The RAAS is regulated by various factors including blood pressure, blood volume, and sodium concentration. Negative feedback mechanisms help to balance the activity of the system to maintain stable physiological conditions.

Clinical Significance

Dysfunction of the RAAS can lead to conditions such as hypertension, heart failure, chronic kidney disease, and renal artery stenosis. Drugs that interfere with the RAAS, such as ACE inhibitors, angiotensin II receptor blockers (ARBs), and aldosterone antagonists, are commonly used to treat these conditions.

See Also

• Blood pressure
• Kidney
• Cardiovascular disease