THE RENIN-ANGIOTENSIN-ALDOSTERONE SYSTEM (RAAS)

 

INTRODUCTION: The renin–angiotensin–aldosterone system (RAAS) is one of the primary homeostatic mechanisms controlling blood pressure and fluid balance in the body. Drugs that affect the RAAS decrease blood pressure and increase urine volume. They are widely used in the pharmacotherapy of Hypertension, heart failure, and myocardial infarction (MI).

PHYSIOLOGY OF RAAS: Renin is an enzyme secreted by specialized cells in the kidney when blood pressure falls, or when there is a decrease in sodium ion (Na+) flowing through the kidney tubules. Once in the blood, renin converts the inactive liver protein angiotensinogen to angiotensin I. When it passes through the lungs, angiotensin I is converted to angiotensin II, one of the most potent natural vasoconstrictors known. The enzyme responsible for the final step in this system is angiotensin-converting enzyme (ACE). The intense vasoconstriction of arterioles caused by angiotensin II raises blood pressure by increasing peripheral resistance. Angiotensin II also stimulates the secretion of aldosterone, a hormone from the adrenal cortex. The primary action of aldosterone is to increase Na+ reabsorption in the kidney. The enhanced Na+ reabsorption causes the body to retain water, increasing blood volume and raising blood pressure.

CONCLUSION: Thus, angiotensin II increases blood pressure through two distinct mechanisms: direct vasoconstriction and increased water retention.

RELATED;

1.  FUNCTION OF THE LIVER

2.  ENZYMES

3.  BLOOD PRESSURE AND HYPERTENSION

4.  HEART FAILURE

REFERENCES