Class 11 NEET Biology Excretory Products and Their Elimination

The Renin-Angiotensin-Aldosterone System (RAAS) is a hormone system that regulates blood pressure and fluid balance. The sequence of events is as follows :
1. Fall in glomerular blood pressure (due to dehydration, sodium deficiency, or hemorrhage, for example) - This is detected by the juxtaglomerular cells (JG cells) in the kidneys.
2. Activation of JG cells and release of renin - In response to low blood pressure, the JG cells release the enzyme renin into the bloodstream.
3. Renin catalyzes the conversion of the protein angiotensinogen (produced by the liver and always present in the blood) into angiotensin I.
4. Angiotensin I is then converted into angiotensin II, a powerful vasoconstrictor that also stimulates the release of aldosterone from the adrenal cortex.
5. Angiotensin II activates the release of aldosterone, which stimulates the reabsorption of sodium ions and water from the distal convoluted tubules in the kidneys, leading to an increase in blood pressure.