Physiology Flashcards
What is GFR
Total volume of plasma per unit time leaving the capillaries and entering the Bowman’s capsule.
normal GFR per day
180 L/d or 120 ml/min.
What is renal clearance?
volume of plasma from which all of a given substance is removed per minute by the kidneys
Renal Clearance measurement
a comparison of the rate of urinary excretion (urine volume x urine concentration of a substance) with the plasma concentration of a substance
What is Creatinine Clearance
- 24 hour creatinine clearance is used clinically as an estimate of GFR (small amount of creatinine excreted).
- It declines with age: d.t. decline in renal function & muscle mass
- Plasma creatinine remains constant for life
Normal value is >100 ml/min.
Measurement of Creatinine clearance
Urine Creatinine clearance x (24 h urine volume/1400)
/
Plasma creatinine concentration/ 1000
What is renal blood flow
RBF= 1200 ml/min of whole blood (approximately 25% of cardiac output)
Does GFR changes with blood pressure?
GFR & Renal flow remain constant within a BP range of 80-180 mmHg.
This through mechanism of autoregulation mediated by changes in afferent arteriolar resistance
Renal Plasma Flow measurement
Commonly measured by para-amino hippuric acid PAH, by determining amount of PAH in the urine per unit time divided by the difference in its concentration in renal arterial or venous blood.
Rate of Renal plasma flow
660ml/min.:
- 120ml/min is filter at glomerulus as ultrafiltrate
- 65% is reabsorbed in PCT
- 14% is reabsorbed in loop of henle
- 15% is reabsorbed in DCT
- 6% is reabsorbed in collecting duct
Urine output average
1.2 ml/min.
only 1% of 120 ml/min of ultrafiltrate filtered by the glomerulus
Furosemide site of action?
ascending limb of Henle’s loop
Site of ADH action
collecting duct
Hormone acting on V2 receptor in kidney
DESMOPRESIN
Mode of action of Acetazolamide
inhbit absorption of HCO3 in proximal convluted tubules
