03/07/2023
RENIN-ANGIOTENSIN-ALDOSTERONE SYSTEM (RAAS)
By Chipo James Mainda
The renin-angiotensin-aldosterone system (RAAS) is the system of hormones, proteins, enzymes and reactions that regulate the blood pressure and blood volume on a long-term basis. It regulates the blood pressure by increasing sodium (salt) reabsorption, water reabsorption (retention) and vascular tone (the degree to which the blood vessels constrict, or narrow).
The renin-angiotensin-aldosterone system (RAAS) involves several steps, including:
• Step I
When renal blood flow is reduced, juxtaglomerular cells in the kidneys convert the precursor prorenin (already present in the blood) into renin and secrete it directly into the circulation. Renal perfusion may be reduced by a decreased cardiac output (heart failure), atherosclerosis, or by systemic arterial vasodilation (e.g., sepsis, liver cirrhosis).
• Step II
Renin will in turn convert Angiotensinogen (which is a protein the liver makes and releases into the bloodstream) to Angiotensin I (inactive hormone).
•Step III
Angiotensin I, which is inactive (doesn’t cause any effects) will be converted into Angiotensin II (an active hormone) by the help of Angiotensin-Converting Enzyme (ACE) produced by the lungs.
• Step IV
* Angiotensin II causes the muscular walls of small arteries (arterioles) to constrict (narrow), which increases blood pressure or blood flow to the kidneys.
* Angiotensin II also triggers the adrenal glands to release aldosterone and the pituitary gland to release antidiuretic hormone (ADH, or vasopressin).
* Together, aldosterone and ADH cause the kidneys to retain sodium. Aldosterone also causes the kidneys to release (excrete) potassium through the urine.
• Step V
The increase in sodium in the bloodstream causes water retention. This increases blood volume and blood pressure, thus completing the renin-angiotensin-aldosterone system.
For more join our daily online lessons on WhatsApp 0977353901.