Renin/Angiotensin (water gain from urine & Na ion and water reabsorption)

• Sensing declining blood pressure or blood volume, juxtaglomerular cells of the nephron release renin, an enzyme that promotes the formation of angiotensin II. • Angiotensin II targets smooth muscle cells in blood vessels that provide blood to the nephron. • Angiotensin II causes these blood vessels to constrict, causing less blood to be filtered by the nephron. • Less water is lost in urine so blood volume and pressure rises. • Declining blood pressure or blood volume sensed by the juxtaglomerular cells of the nephron releases renin, an enzyme that promotes the formation of angiotensin II. • Angiontensin II targets zona glomerulosa cells of the adrenal cortex. • Increased angiotensin II promotes the production of aldosterone, another urinary hormone. • Aldosterone promotes reabsorption of ions from urine and indirectly promotes reabsorption of water back into the bloodstream. This results in an increase in blood volume and pressure. Increased blood pressure • Declining blood pressure or blood volume sensed by the juxtaglomerular cells of the nephron releases renin, an enzyme that promotes the formation of angiotensin II. • Angiontensin II targets cells in the proximal convoluted tubule of the nephron within the kidney. • The reabsorption of Na+ and Cl- ions sets up an osmotic gradient favoring the retention of water. • Less water is lost in urine so blood volume and pressure rises. • In Summary: • Renin promotes the production of angiotensin II. • Angiotensin II causes vasoconstriction of arterioles. • Angiotensin II promotes production of aldosterone. • Aldosterone promotes reabsorption of ions and water. • Angiotensin II promotes the reabsorption of Na+ and Cl- ions favoring the retention of water. • These combined activities result in increased blood volume and pressure.

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