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Renin Angiotensin Mechanism.

Renin-Angiotensin-Aldosterone-System (RAAS).

Renin-Angiotensin-Aldosterone-System (RAAS).

  • Renin is a proteolytic enzyme that is secreted by the juxtaglomerular apparatus (composed by renin-secreting cells) when certain physiological stimuli such as reduced renal perfusion pressure and reduced NA+ concentration in distal tubular fluid are present. 
  • Renin will cut angiotensinogen (released into circulation by the liver) into a shorter peptide called angiotensin I. 
  • Angiotensin-conversing enzyme (ACE) then remove 2 amino acids from angiotensin I to form an octapeptide called angiotensin II. 
  • Amino peptidase A and N will remove amino acids from angiotensin II to angiotensin III and angiotensin IV respectively. 
  • ACE is an enzyme normally found on the surface of endothelial cells and is abundant in the lungs.
  • Angiotensin II is  a potent vasoconstrictor that causes arterioles to constrict resulting in increased arterial blood pressure, angiotensin II also stimulates the secretion of aldosterone from adrenal cortex. 
  • Angiotensin III stimulates aldosterone secretion and is involved in thirst. 
  • Angiotensin IV associated with the release of plasminogen activator inhibitor-1 from the endothelium. 
  • Aldosterone acts on the tubular epithelial cells of the kidneys to stimulate reabsorptions of NA+ and water.


Key points:

  1. Angiotensinogen is released in the blood circulation by "liver".
  2. Renin is released in the blood circulation by "Kidney" in response to fall in blood pressure and fluid volume of the body.
  3. Renin acts on "inactive Angiotensinogen" and converts it into "Angiotensin-I".
  4. Through blood "Angiotensin-I" reaches Lungs where it get converted to active "Angiotensin-II" by action of the enzyme "Angiotensin Converting Enzyme".
  5. "Angiotensin-II" directly acts on "Adrenal Gland" and releases "Aldosterone".
  6. "Angiotensin-II" also acts directly on blood vessels causing "vasoconstriction" this results directly in "rise of the blood pressure".
  7. "Aldosterone" is a powerful "Mineralocorticoid" acts directly on "Distal Convoluted Tubule of the Kidney" and results in reabsorption and retention of "Na and Water" this results in "increased circulating plasma level and hence rise in Blood Pressure."

"Various drugs are available which act on different stages of "Renin-Angiotensin-Aldosterone-System (RAAS)." and are employed in the management of hypertension and various CVS disorders."

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