Renin–angiotensin–aldosterone system
Say it: REE-nin an-jee-oh-TEN-sin al-DOS-tuh-rohn SIS-tum
The renin–angiotensin–aldosterone system is a hormone cascade, begun by renin from the kidneys, that raises blood pressure and blood volume when they fall.
Also: RAAS, renin-angiotensin system
Definition
What is the renin–angiotensin–aldosterone system?
The renin–angiotensin–aldosterone system (RAAS) is a chain of enzymes and hormones that guards blood pressure, blood volume and salt balance. It starts in the kidney, where juxtaglomerular cells in the wall of the afferent arteriole release the enzyme renin when blood pressure falls, when less salt reaches a sensing region of the nephron, or when sympathetic nerves stimulate them.
Renin cuts angiotensinogen, a protein made by the liver, to form angiotensin I. Angiotensin-converting enzyme (ACE), found on the inner lining of blood vessels and especially plentiful in the lungs, then turns angiotensin I into angiotensin II, the active hormone. Angiotensin II narrows arterioles, raising blood pressure within minutes, and it also stimulates thirst and the release of antidiuretic hormone. In addition it prompts the adrenal cortex to secrete aldosterone, which makes the kidneys hold on to sodium and, with it, water, expanding blood volume over hours to days.
Because an overactive system contributes to high blood pressure, heart failure and kidney disease, it is a major drug target. ACE inhibitors block the formation of angiotensin II, angiotensin II receptor blockers stop it from acting, and aldosterone antagonists block the receptor for the final hormone.
Word parts
Where does the term “renin–angiotensin–aldosterone system” come from?
- ren-
- kidneyLatin renes, kidneys
- angi-
- vesselGreek angeion
- -tensin
- tension, pressureLatin tendere, to stretch
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Terms that go with it
- AldosteroneAldosterone is a steroid hormone from the adrenal cortex that makes the kidneys keep sodium and water and excrete potassium, raising blood volume.
- Juxtaglomerular apparatusThe juxtaglomerular apparatus is a cluster of specialized kidney cells beside each glomerulus that senses salt and blood pressure and releases renin.
- Blood pressureBlood pressure is the force that circulating blood exerts on the walls of the arteries, recorded as systolic over diastolic pressure in mm Hg.
- HypertensionHypertension is a long-term condition in which the pressure of blood against artery walls stays higher than normal, straining the heart and vessels.
- Antidiuretic hormoneAntidiuretic hormone is a peptide hormone made in the hypothalamus and released by the posterior pituitary that makes the kidneys keep water.
- KidneyThe kidneys are two bean-shaped organs that filter the blood to make urine, balancing the body's water, salts and acid and helping set blood pressure.
Sources
Checked against
Written for biofideX in plain words, after checking these references:
- OpenStax Anatomy and Physiology 2e, 25.8 Endocrine Regulation of Kidney Function
- OpenStax Biology 2e, 41.5 Hormonal Control of Osmoregulatory Functions
- NCBI MeSH: Renin-Angiotensin System
- MedlinePlus Medical Tests: Renin Test
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