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The Renin-Angiotensin-Aldosterone (RAA) Pathway

The Renin-Angiotensin-Aldosterone (RAA) Pathway. The First Stages. Person is dehydrated, has a sodium ion deficiency or is hemorrhaging, any of these stimuli will initiate the pathway All of these conditions cause a decrease in blood volume

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The Renin-Angiotensin-Aldosterone (RAA) Pathway

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  1. The Renin-Angiotensin-Aldosterone (RAA) Pathway

  2. The First Stages • Person is dehydrated, has a sodium ion deficiency or is hemorrhaging, any of these stimuli will initiate the pathway • All of these conditions cause a decrease in blood volume • This leads to decreased blood pressure and juxtaglomerular cells in the kidneys are stimulated to release the enzyme RENIN • This in turn increases blood levels of renin

  3. Second Stages • Renin will convert angiotensinogen (plasma protein made by the liver) into angiotensin I. • Blood levels of Angiotensin I rise as a result. • As blood flows another enzyme (Angiotensin-converting enzyme) (ACE), converts Angiotensin I into Angiotensin II. • Blood levels of Angiotensin II now rise. • Angiotensin II stimulates the adrenal cortex to secrete aldosterone

  4. Third Phase • In the kidneys, increased aldosterone levels cause an increase in the reabsorbing of sodium ions and water • Retain more, urinate less of both • Aldosterone also stimulates the kidneys to increase secretion of potassium and hydrogen ions into urine • Increased water retention increases the blood volume • This in turn increases blood pressure and brings it back to normal

  5. Third Phase Continued • In addition to increased blood volume, Angiotensin II also stimulates vasoconstriction of arterioles which increases blood pressure as well • Under normal circumstances this should return blood pressure back to normal.

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