Question

In response to low blood pressure, the RAS (aka RAAS) system is activated. Discuss how it restores blood pressure back to homeostasis.

Answer 1

When there is a lowering of blood pressure, RAAS helps in restoring the pressure.

When there is a decrease in the blood pressure, renin is released from the juxtaglomerular cells of the kidney. Renin stimulates the production of angiotensin in blood and tissues, and it stimulates the release of aldosterone from the adrenal cortex.

Renin Release

Renin released from JG cells in response to 3 factors

1)Decreased sodium entry to DCT

2)Renal artery hypotension

3)Sympathetic nerve stimulation

Production of Angiotensin II

When renin is released, it will convert angiotensinogen (which is produced in liver) to angiotensin I.

Angiotensin I is converted to angiotensin II in the lungs by the help of enzyme called angiotensin converting enzyme (ACE)

Binding of Angiotensin II
Angiotensin II binds to receptors throughout the body and exerts its action

• Adrenal cortex-- release of aldosterone
• Kidney-- Na+ reabsorption
• Arterioles-- vasoconstriction
• Sympathetic nervous system-- release of Nor adrenaline
• Hypothalamus-- ADH release and increase thirst

Aldosterone
It is a mineralocorticoid which is secreted from zona glomerulosa of adrenal cortex.

It acts on principal cells of collectong duct and causes salt and water retention and increases K+ and H+ excretion.

This will cause increase in the volume of extracellular fluid in body and thus increases blood pressure.