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Kidney Endocrine Functions

Topic updated on 11/06/17 2:18pm

Introduction
  • The kidneys are also involved in promoting erythropoiesis and producing activated vitamin D
    • erythropoiesis (red blood cell production)
      • the kidneys produce a glycoprotein growth factor called erythropoietin (EPO)
        • in hypoxia, there is less O2 being delivered to the kidneys
          • this in turn causes the production of hypoxia-inducible factor-1α (HIF-1α) which acts on the fibroblasts in the renal cortex to transcribe EPO (increased EPO mRNA)
            • EPO promotes the differentiation of proerythroblasts to eventually form into erythrocytes (red blood cells)
              • note that one can commonly see anemia in patients with chronic renal failure since the functioning renal mass is decreased
                • this is why recombinant human EPO is a treatment for anemia of chronic renal failure
    • vitamin D production
      • the kidneys contain an enzyme called 1α-hydroxylase
        • 1α-hydroxylase catalyzes the hydroxylation (at the C1 position) of 25-hydroxycholecalciferol into 1,25-dihydroxycholecalciferol
          • 1,25-dihydroxycholecalciferol is a physiologically active form of vitamin D
            • in the kidney, 25-hydroxycholecalciferol can also be hydroxylated (at the C24 position) into 24,25-hydroxycholecalciferol, an inactive form of vitamin D
          • 1α-hydroxylase is regulated by a number of factors such as
            • plasma Ca2+ concentration
              • a decrease in plasma Ca2+ increases 1α-hydroxylase activity
            • parathyroid hormone
              • increases 1α-hydroxylase activity
            • plasma phosphate concentration
              • a decrease in plasma phosphate increases 1α-hydroxylase activity
  • Prostaglandins 
    • the kidneys locally produce prostaglandins (e.g., PGE2) that result in vasodilation of the afferent and efferent arteriole
      • this in turn increases renal blood flow
      • nonsteroidal antiinflammatory drugs (NSAIDs) impair prostaglandin synthesis
        • the renoprotective effects of prostaglandins are loss in low blood volume states (e.g., hemorrhage)
  • Dopamine
    • low levels of dopamine dilates the renal arterioles and thus increases renal blood flow
      • secreted by proximal tubular cells to promote natriuresis
 


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