Glomerular Filtration Rate Flashcards
What are the 3 barriers to filtration
1- capillary endothelium
2- fused basement membrane
3- podocyte foot processes
List Filtrate composition
1- Plasma protein ( small ones ) 2- H20 3- Glucose 4- Electrolytes 5- amino acids 6- fatty acids 7- Nitrogenous wastes
Do RBC pass the filtration barrier
no
What is Proteinuria
protein in the urine
What is Hematuria
Blood in urine
What might cause Proteinuria and Hematuria
- Hypertension
- Kidney infection ( infection of podocytes and slits )
Why might leukocytes be seen in urine
UTIs
What is the net filtration pressure
difference between pressures that force fluid out vs in
What affects the arterial end NFP
The hydrostatic pressure in the artery causes fluid to be pushed out
Osmotic pressure in artery keeping fluid in
What type of pressure is greater in arterial end NFP
Hydrostatic pressure is greater than osmotic causing fluid to move out of capillary
What type of pressure is greater in venous end NFP
Osmotic pressure is greater than hydrostatic pressure causing fluid to move into venule
What determines hydrostatic pressure in glomerular capillaries
1- arterial pressure
2- greater resistance in efferent than afferent
What determines hydrostatic pressure in Bowman’s capsule
1- pressure of filtrate in capsule
Is HPgc greater than or less than HPbc
greater
What effects the osmotic pressure in glomerulus and Bowman’s capsule
the protein in the plasma and filtrate
Does plasma in GC or filtrate in BC have more proteins and thus osmotic pressure
Plasma has more protein as filtrate has close to none and thus plasma in GC has higher osmotic pressure
What determines the GFR
the net filtration rate and a constant that represents the ease which fluid can move through pore
What is the NFP for Glomerular filtration
Usually net filtration number causes fluid to be pushed out since hydrostatic pressure is greater than osmotic.
How is GFR measured
By measuring the clearance rate of a substance from blood into the urine. substance is freely filtered and not reabsorbed or secreted by kidneys.
What’s the equation for GFR
( Urine substance x urine flow) / plasma substance
What can be used to measure GFR
1- Inulin IV with repeated blood and urine collections.
2- creatinine levels
What is the side effect of using inulin to measure GFR
inaccuracy due to incomplete bladder voiding
Why is creatinine used to measure GFR and what are the possible complications
- naturally produced by body and freely filtered in glomerulus
- creatinine is secreted by peritubular capillaries so creatinine clearance might overestimate GFR but if measured in plasma levels then its more accurate
can the measuring of GFR be completely accurate
No , equations are used to count in age, sex, weight and still not fully accurate
What factors may affect GFR
1- Kidney disease : reduces
2- Hypertension : damage to GC
3- Sleep : hormonal and oncotic variations
4- exercise : blood flow diverted to muscles
5- Renal blood flow reduced
Why is measuring renal blood flow important clinically
to determine nature of renal disease
What keeps GFR constant
normal range of Blood pressure because renal blood flow stays constant
What keeps renal blood flow constant
autoregulation myogenic vasoconstriction in kidney
What is important to think about when wanting to measure renal blood flow
Substance should be cleared in 1 circuit through Kidney
What is used to measure renal blood flow and why
Para-aminohippuric acid ( PAH). Doesn’t effect kidney function , not metabolized by body and more than 90% is extracted in 1 circuit
What is the disadvantage of using PAH to measure renal blood flow
PAH is confined to plasma so doesn’t directly measure renal blood. must measure plasma flow first then convert it to renal blood flow once taking into account Haematocrit
What is the formula for measuring Renal plasma flow by PAH
( Urine of PAH x urine flow rate ) / arterial plasma of PAH
Formula to change Renal plasma flow to renal blood flow
RPF / ( 1-HCT )
