Physiology
Renal Physiology
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- Interstitial ion concentrations including acid-base balance
- Waste excretion
- Erythropoiesis
Vitamin D metabolism: hydroxylation of 25-hydroxycholecalciferol to 1,25-dihydroxycholecalciferol
- Prostaglandin and kinin production
- Glomerular filtration
- 20% of renal plasma flow is filtered: 120ml/min
- Filtration governed by Starling’s law
Blood pressure in the glomerular capillaries is autoregulated so filtration can remain constant across a range of systemic pressures
- Reabsorption
- The renal tubules reabsorb a constant fraction of the sodium filtered
- 95-99% of sodium is actively reabsorbed
Proximal tubules: this is coupled with glucose and amino acid co-transport (secondary active transport)
- ADH: increases permeability of the collecting ducts to water
Potassium is reabsorbed passively and actively in the proximal tubules and secreted back into urine under the influence of aldosterone in the distal tubules
- ADH also affects potassium excretion
The ascending limb of the loop of Henle is impermeable to water. This supports the countercurrent exchange mechanism that allows water reabsorption
- Sodium is pumped out of the ascending limb creating a hypertonic interstitium