Renin–angiotensin system

File:Renin-angiotensin system in man shadow.svg

Renin-angiotensin system in man shadow

File:Renin-angiotensin-aldosterone system.svg

Renin-angiotensin-aldosterone system

File:Renin angiotensin aldosterone system.png

Renin angiotensin aldosterone system

Renin–Angiotensin System (RAS) is a hormone system within the body that is essential for the regulation of blood pressure and fluid balance. It plays a critical role in the body's cardiovascular and renal systems, influencing both heart function and kidney operation. The system operates through a series of reactions that produce angiotensin, a peptide hormone that causes vasoconstriction and an increase in blood pressure. The RAS is a target for drugs that treat hypertension (high blood pressure), heart failure, and chronic kidney disease.

Overview

The Renin–Angiotensin System begins with the release of renin, an enzyme, by the kidneys when there is a decrease in blood volume or blood pressure, or an increase in sodium concentration in the urine. Renin converts angiotensinogen, a large protein produced by the liver, into angiotensin I. Angiotensin I is then converted into angiotensin II by angiotensin-converting enzyme (ACE), which is found in the lungs and other tissues. Angiotensin II is a potent vasoconstrictor, narrowing the blood vessels and increasing blood pressure. It also stimulates the release of aldosterone from the adrenal gland, which leads to the absorption of sodium and water by the kidneys, further increasing blood pressure.

Components

• Renin: An enzyme secreted by the kidneys that starts the process by converting angiotensinogen to angiotensin I.
• Angiotensinogen: A precursor molecule produced by the liver, which is converted into angiotensin I by renin.
• Angiotensin I: A decapeptide that is converted into angiotensin II by ACE.
• Angiotensin-Converting Enzyme (ACE): An enzyme that converts angiotensin I to angiotensin II.
• Angiotensin II: A potent vasoconstrictor that increases blood pressure and stimulates aldosterone release.
• Aldosterone: A hormone that increases sodium and water reabsorption by the kidneys, raising blood pressure.

Function

The primary function of the RAS is to maintain blood pressure, fluid balance, and sodium balance in the body. It is activated in response to hypotension (low blood pressure), hyponatremia (low sodium concentration), or dehydration. The system helps to restore blood pressure and volume by increasing sodium and water reabsorption in the kidneys, and by increasing vascular resistance through vasoconstriction.

Clinical Significance

The Renin–Angiotensin System is a significant target for the treatment of cardiovascular diseases. Drugs that inhibit the RAS, such as ACE inhibitors and angiotensin II receptor blockers (ARBs), are commonly used to treat hypertension, heart failure, and chronic kidney disease. These medications help to lower blood pressure and reduce the workload on the heart.

Pathophysiology

Dysregulation of the RAS can lead to various cardiovascular and renal diseases. Overactivity of the RAS can result in hypertension, which is a major risk factor for stroke, myocardial infarction (heart attack), and kidney failure. Conversely, underactivity of the RAS can lead to hypotension and renal failure.

See Also

• Blood pressure
• Cardiovascular disease
• Hypertension
• Kidney
• Heart failure

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