Renal – Functions

Master answer

1. Excretion of metabolic waste and foreign substances
   • Filtration of metabolic waste products
     • urea from protein
     • uric acid from nucleic acids
     • creatinine from muscle creatine
   • Filtration of drugs
2. Regulation of water and electrolyte balance
   • Homeostatic mechanism
   • 180L of fluid and other substances per day, with 99% reabsorbed along the tubule
   • Concentration of urine via the countercurrent mechanism
     • max 1400mOsm to reduce renal water loss
   • Reabsorb K, Ca, Mg and Cl either passively or actively
3. Regulation of plasma osmolality
   • Plasma osmolality is altered whenever the inputs and outputs of water and solutes changes disproportionately.
   • Input from the hypothalamic osmoreceptors contributes.
4. Regulation of acid base balance
   • Excretion of H+ ions, fixed acids, phosphate and ammonium
   • Resorption of HCO3- to maintain plasma neutrality
5. Regulation of blood pressure
   • Production of angiotension 2 via the RAAS in response to a reduction in GFR system
     • peripheral vasoconstriction
     • reabsorption of sodium
     • secretion of aldosterone
       • → rise in MAP
   • Changes in blood volume regulated by the kidney (as mentioned above) will also influence BP
6. Endocrine function
   • Vitamin D
   • EPO to stimulate RBC production (in response to a reduction in pO2 the secretory cells which lie in between the cortex and medulla)
   • Aldosterone and angiotensin II as regulated by the RAAS will contribute to BP management
   • Prostaglandins esp PGE2 and prostacyclin – potent renal vasodilators
   • Bradykinin – potent renal vasodilator
7. Gluconeogenesis
   • The renal cortex contains glucose-6-phosphatase and thus the ability to release glucose in times of need

Gladwin 2016

Answer by Gladwin