Renin Angiotensin Mechanism.

Introduction.

Also known as, Renin-Angiotensin-Aldosterone System (RAAS).
The Renin-Angiotensin-Aldosterone System is a hormone system that regulates blood pressure by maintaining fluid balance in the body.
Dehydration, Sodium deficiency or hemorrhage are main causes of decreasing circulating plasma levels.
Decreased circulating plasma levels cause low Blood Pressure (low BP).
Decreased circulating plasma levels stimulate the “Juxtaglomerular apparatus”.
Juxtaglomerular apparatus secretes a protein called “Renin” in plasma.
Renin activates Angiotensinogen, a plasma protein secreted by the liver in plasma to Angiotensin I.
On reaching the lungs, the Angiotensin I present in plasma gets converted to the active form Angiotensin II by action of the enzyme “Angiotensin Converting Enzyme (ACE)”.
The formed Angiotensin II acts on Angiotensin II receptors present on the Adrenal gland and releases “Aldosterone”.
Aldosterone directly acts on kidneys and ↑ Sodium and water reabsorption.
As more water is reabsorbed, circulating plasma volume increases causing increased blood pressure.
Angiotensin II also causes vasoconstriction of arterioles causing a direct increase in blood pressure.
Various drugs are designed which can interfere with the RAAS, to treat hypertension. (Click here for information on drugs acting on RAAS)