College Answer

It was expected that candidates would discuss the major hormones produced (or activated) by the kidney. These included erythropoeitin, renin and calcitriol. Good answers included the following: the area where the hormone is produced or modified; stimuli for release; factors which inhibit release; and the subsequent actions / effects. Marks were not awarded for hormones that act on the kidney

Discussion

• Hormones which are secreted by the kidney
  • Erythropoietin
    • Secreted from modified cortical fibroblasts
    • Stimulated by hypoxia and angiotensin II
    • Inhibited by inflammatory cytokines
    • Effect is increase in the rate of red cell production and maturation
  • Renin
    • Secreted from juxtaglomerular cells
    • Stimulated by hypotension, sympathetic activation and decreased renal salt delivery
    • Inhibited by angiotension II and normalised blood pressure/volume
    • Effect is to activate RAAS, producing vasoconstriction and salt/water retention
  • Thrombopoietin
    • Secreted from the proximal convoluted tubule
    • Stimulated by thrombocytopenia and inflammatory cytokines
    • Inhibited by itself (negative feedback loop)
    • Effect is to stimulate megacaryocytes and increase platelet production
  • Urodilatin
    • Secreted from DCT cells, directly into the tubule
    • Stimulated (probably) by increased sodium delivery
    • Inhibited (presumably) by decreased sodium delivery
    • The effect to increase sodium reabsorption in the collecting duct
• Hormones which are modified by the kidney
  • Calcitriol (active form of Vitamin D)
    • Modified in the proximal tubule
    • Increased  conversion is stimulated by hypocalcemia, PTH and low vitamin D levels
    • Conversion is inhibited by hypercalcemia, low PTH and high vitamin D levels
    • Physiological role is to increase calcium levels by increasing renal/GI absorption and enhancing osteoclast activity
• Hormones which are cleared or metabolised by the kidney
  • Insulin
    • 90% cleared by the kidney (proximal tubule)
  • Gastrin
    • 30% cleared by the kidney (probably also proximal tubule)
  • Other hormones:
    • PTH
    • Vasopressin
    • Oxytocin
    • TSH
    • Growth hormone
    • Luteinising hormone

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