03 Renal Blood Flow and Glomerular Filtration Flashcards
(12 cards)
Define ultratfiltration
formation of ultrafiltrate from plasma in the glomerulus
What is the marker for renal failure
Reduced glomerular filtration rate
Describe the specialised organisation of the glomerulus and Bowmen’s capsule
Fenestrated endothelium
Fenestrated basement membrane
Podocytes
How do you calculate ultrafiltration pressure
Ultrafiltration pressure = hydrostatic pressure - oncotic pressure - tubule pressure (45 - 25 - 10 = 10 mm Hg)
How do you calculate GFR. List the factors that can affect GFR related to the equation
Ultrafiltration pressure x Pf (ultrafiltration coefficient)
Surface area and permeability
Define GFR
The amount of plasma that is freely filtered from glomerulus into Bowman’s capsule ml per unit time
Define another way of calculating GFR
Renal plasma flow x filtration fraction which the latter is typically 20%
What happens to GFR when there is increase in BP
No net effect as there is myogenic vasoconstriction in response to the rise in BP so the flow remains the same
Define clearance
The number of litres of a substance in plasma that is completely cleared per unit time
Clearance = urinary flow rate x [substance] / plasma flow rate
What are the characteristics of a substance that allows GFR to be measured
Substance that is:
1) freely filtered
2) not reabsorbed nor secreted
3) non toxic
4) measurable
What can be used as the measurement for renal plasma flow and why
PAH (para aminohippurate) because it is freely filtered plus secreted. Therefore the amount cleared is equal to renal plasma flow
Why is renal clearance an important indication diagnostically
If there is impaired clearance means drug dosage may need to be altered as some take into account of renal clearance
