Renal Physiology

Renal Physiology

·        Function of kidneys:

o   Maintenance of fluid and electrolyte balance

o   Excretion of metabolic wastes

o   Excretion of acid

o   Endocrine (calcitriol, erythropoietin)

·        Allows regulation of a daily intake of:

o   Water: 1 – 20 litres

o   Sodium: 5 – 500 mmol

o   Potassium: 20 – 200 mmol

o   Protein: 30 – 150 g

·        Fluid dynamics:

o   Kidney‟s receive 20 – 25% of cardiac output

o   GFR maintained by autoregulation but dependent on glomerular pressure and renal blood flow

o   Normal urination: 1 ml/kg/hr (down to 0.5 ml/kg/hr OK)

o   Urine output of 1 – 2 litres/day

·        Hormones:

o   Intra-renal:

§  Renin-angiotensin system: ¯Na, hypotension ® ­renin ® ­angiotensin II ® vasoconstriction, ­aldosterone and thirst

§  Prostaglandins: vasodilating, control glomerular blood flow, natriuretic and diuretic

o   Extra-renal:

§  Aldosterone: stimulated by Angiotensin II and ­K ® Na reabsorption

§  ADH: controlled by both volume and osmotic stimuli ® ­water resorption providing sufficient medullary concentration gradient

§  Atrial and brain natriuretic proteins (ANP/BNP): volume overload ® natriuretic and diuretic

·        For hypo/hypernatraemia, potassium and acid-base balance