Question 4

Describe the endocrine functions of the kidney.

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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

References

Acharya, Vinay, and Juan Olivero. "The kidney as an endocrine organ." Methodist DeBakey cardiovascular journal 14.4 (2018): 305.

Henderson, Jenny, and Ian W. Henderson. "The endocrine functions of the kidney." Journal of Biological Education 28.4 (1994): 245-254.

Souma, Tomokazu, Norio Suzuki, and Masayuki Yamamoto. "Renal erythropoietin-producing cells in health and disease." Frontiers in physiology 6 (2015): 167.

Pagel, H., W. Jelkmann, and C. Weiss. "Erythropoietin production in the isolated perfused kidney." Biomedica biochimica acta 49.2-3 (1990): S271-4.

Jelkmann, Wolfgang. "Regulation of erythropoietin production." The Journal of physiology 589.6 (2011): 1251-1258.

Jelkmann, Wolfgang EB, et al. "Inhibition of erythropoietin production by cytokines: implications for the anemia involved in inflammatory states." Annals of the New York Academy of Sciences 718.1 (1994): 300-311.

Sungaran, R., B. Markovic, and B. H. Chong. "Localization and regulation of thrombopoietin mRNA expression in human kidney, liver, bone marrow, and spleen using in situ hybridization." Blood, The Journal of the American Society of Hematology 89.1 (1997): 101-107.

Stockelberg, D., et al. "Plasma thrombopoietin levels in liver cirrhosis and kidney failure." Journal of internal medicine 246.5 (1999): 471-475.

Forssmann, Wolf-Georg, Markus Meyer, and Kristin Forssmann. "The renal urodilatin system: clinical implications." Cardiovascular research 51.3 (2001): 450-462.

Norman, Anthony W. "From vitamin D to hormone D: fundamentals of the vitamin D endocrine system essential for good health." The American journal of clinical nutrition 88.2 (2008): 491S-499S.

Rabkin, R., A. H. Rubenstein, and J. A. Colwell. "Glomerular filtration and proximal tubular absorption of insulin 125 I." American Journal of Physiology-Legacy Content 223.5 (1972): 1093-1096.

Davidson, Warren D., Peter D. Springberg, and Newell R. Falkinburg. "Renal extraction and excretion of endogenous gastrin in the dog." Gastroenterology 64.5 (1973): 955-961.