Glomerular Filtration Rate: Understanding Kidney Function

Glomerular Filtration Rate: Understanding Kidney Function

Question 1. What is glomerular filtration rate? How it is measured?
Answer:

Glomerular filtration rate:

• Definition:
  • Glomerular filtration rate is the total quantity of filtrate formed in all the nephrons of both the kidneys in the given unit of time.
• Value:
  • 125 ml/min.
  • About 170-180 litres/day.
• Pressure determining filtration:
  1. Glomerular capillary pressure favours GFR
  2. Colloidal osmotic pressureopposes GFR.
  3. Hydrostatic pressure in Bowman’s capsule opposes GFR.
• Measurement of GFR:
  • Effective filtration pressure glomerular hydrostatic pressure [colloidal osmotic pressure + Intracapsular pressure]
    = [Hydrostatic pressure in glomerular capillaries hydrostatic pressure in Bowman’s capsule][colloidal osmotic pressure + Intracapsular pressure]
    = [45-10]-[25+0] = 35-25=10.
  • Now, GFR Kf x EFP.
  • kf Filtration coefficient of the glomerular membrane 12.5 ml/min/mm Hg.
  • Thus, GFR = Kf x EFP
    = 12.5 × 10
    = 125 ml/min.

Question 2. Define renal clearance of tubules. What is its significance?
Answer:

• Renal clearance:
• Definition:
  • It is the amount of plasma that is cleared off a substance in a given unit of time.
  • It is based on Fick’s principle.
• Factors determining renal clearance:
  1. Volume of urine excreted [V]
  2. Concentration of the substance in urine [U]
  3. Concentration of the substance in blood [P]
     Clearance = \(\frac{UV}{P}\)
• Significance:
  1. Renal clearance helps in assessment of.
  2. Glomerular filtration rate.
  3. Renal plasma flow.
  4. Renal blood flow.