GFR Physiology

Lecture given:


Describe glomerular filtration and the glomerular filtration rate

  • GFR: volume of fluid filtered from the renal glomerular capillaries into the Bowman's capsule per unit time (corrected for body surface area)
  • Glomerular filtration: bulk flow of protein free plasma from the glomerulus into Bowman's space
    • Same salt composition as plasma at the beginning
    • Filtrate composition changes in its passage down the nephron

Describe how Starling Forces influence fluid movement a) between capillaries and interstitial fluid and b) between capillaries and Bowman's capsule

  • Starling forces: (out of capillary is +)
    • Capillary hydrostatic pressure (+)
    • Interstitial fluid colloidal oncotic pressure (+)
    • Capillary fluid colloidal oncotic pressure (-)
    • Interstitial fluid hydrostatic pressure (-)
      • Usually 0
  • Movement to Bowman's capsule
    • Size: small molecules (~5000) has easier time moving than larger molecules (Hgb ~68K, Albumin ~69k)
    • Charge: Glomerular basement membrane is negatively charged, so will repel negatively charged molecules
  • Autoregulation
    • GFR maintained over a wide gradient of blood pressure
    • Through dilation/constriction of A/Efferent arterials controlled by feedback loops, myogenic stretch responses and neurohormonal influences
      • Aff art dilatation: prostaglandin, kinine, dopamin (low dose), ANP, NO
      • Eff art constriction: Angiotensin II
      • Aff art constriction: norepinephrine, endothelin, ADH, prostaglandin blockade
      • Eff art dilatation: Angiotensin II blockade
    • Juxtamedullary apparatus
      • macula densa senses the ionic content of tubular fluid at the thick ascending limb/DCT
      • stretch receptors cause renin release, which is involved in formation of angiotensin II and release of aldosterone
  • In case of reduction in GFR:


  • In case of increase in GFR:
    • Macula densa sense increase in delivery and reabsorption of chloride
    • vasocontrict afferent arterial
    • Tubulo-glomerular Feedback
    • inhibited by loop diuretics

Given the necessary information, calculate net filtration pressure

  • Filtration = Kf (ΔP - Δπ)


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