Describe the endocrine functions of the kidney.
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
- Hormones which are secreted by the kidney
- 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
- 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
- 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
- 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
- Calcitriol (active form of Vitamin D)
- Hormones which are cleared or metabolised by the kidney
- 90% cleared by the kidney (proximal tubule)
- 30% cleared by the kidney (probably also proximal tubule)
- Other hormones:
- Growth hormone
- Luteinising hormone
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