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21 Cards in this Set
- Front
- Back
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How is RPF calculated?
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Using the clearance equation with PAH
RPF= C(PAH)=[U]pah x V ___________ [P]pah where C(pah) = clearance of PAH, [U]pah= urine concentration of PAH, V= urine flow rate, [P]pah= plasma conc of PAH |
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How do you measure RBF/
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RBF= RBF
_________ 1- hematocrit where 1- hct is the fraction of blood occupied by plasma. |
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What substance is used tom measure the GFR? Why?
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Inulin, it is filtered but not reabsorbed or secreted by the renal tubules.
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What equation is used to measure GFR?
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Using the clearance equation with inulin:
GFR= C(inulin)= [U]inulin xV __________ [P]inulin where C(inulin)= clearance of inulin [U]= urine conc of inulin, V= urine flow rate [P]inulin= plasma conc of inulin |
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What can be used clinically to approximate GFR?
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Creatinine(Cr) clearance
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Does GFR remain constant with aging?
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No, it decreases with age
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What happens to blood urea nitrogen(BUN) and plasma Cr when GFR decreases?
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Increases since both are filtered by the glomerulus.
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What happens to plasma Cr with age?
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It remains relatively constant despite the decrease in GFR with age due to the decrease in muscle mass seen with aging.
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What are Starling forces?
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The collection of factors that are the driving force for glomerular filtration
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What is the Starling equation?
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GFR= K(f)[(P(cg-P(bs)-(piegc-piebs)]
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describe all of the term used in the Starling equation.
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K(f)=filtration coeffecient across the glomerular barrier
P(gc)=hydrostatic pressure in the glomerular capillary. This value is constant along the length of the capillary. P(bs)= Hydrostatic pressure in Bowman's space Pie(gc)=Oncotic pressure in the glomerular capillary. It increases along the length of the glomerular capillary because water is filtered off, which increases the concentrated of protein and increases the oncotic pressure. |
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What does Pie(bs) mean in the Starling equation?
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Oncotic pressure in Bowman's space.
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What are the components of the glomerular filtration barrier?
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1. Fenestrated capillary endothelium
2. Fused basement membrane with heparin sulfate 3. Epithelial layer consisting of podocyte foot processes. |
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What is the normal value of Pie(bs)?
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Zero. The protein conc in Bowman's space is so small that it may be ignored.
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What can cause an increase in P(gc)? What is the effect on GFR?
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Dilation of the afferent arteriole or constriction of the efferent arteriole. This will increase GFR.
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What can cause an increase in P(bs)?
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Constriction or blockage of the ureters. This will increase GFR.
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What can cause an increase in Pie(gc)?
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Increase in protein concentration. This decreases GFR.
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What aspect of the filtration barrier restricts plasma proteins from being filtered?
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Anionic glycoproteins(heparan sulfate) that line the barrier repel the negatively charged proteins.
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What is the filtration fraction? (FF)
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The fraction of RPF that is filtered across the glomerular capillary.
It is calculated: FF= GFR ____ RPF Its normal value is 0.20 or 20%. |
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What happens to the protein concentration in the peritubular capillaries with increasing FF.
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Increases
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The following values were found while studying a glomerulus:
afferent arteriole pressure= 30mm Hg, oncotic pressure of glomerular capillary = 25mmHg, Bowman's space pressure= 12mmHg. From these values, determine whether filtration will be favored or not. |
net pressure is dtermined from the Starling equation by excluding the filtration constant, and recognizing that Pie(bs) is zero.
The equation can be written as: net pressure=(Pgc-Pbs)-(Pie(gc)-0) Plugging the numbers in: (30 -12) - (25)= -7 mm Hg. Therefore, filtration is not filtered. A positive number represents a net pressure that favors filtration, because the factors promoting filtration outweigh those that inhibit it. In this case, they do not. |
