Lecture 2: Filtration and Clearance (Bolsor) Flashcards
what is the filtration barrier between glomerular capillary and Bowman’s capsule composed of? (3 components)
glomerular capillary endothelium, basement membrane, and epithelial podocytes of Bowman’s capsule
3 main characteristics of filtrate
1) virtually protein-free
2) solute concentrations are the same as plasma
3) formed as a result of hydrostatic and oncotic pressure differences across the glomerular membrane
why does more blood enter the Bowman’s capsule through the afferent arterioles than leaves through the efferent arterioles?
some is filtered out through the capillaries inside the capsule
Is it normal to have protein in urine?
NO
increased molecular size –> ability to filtrate that molecule in Bowman’s capsule
decreases
which molecule filters more easily in the kidney: myoglobin or hemoglobin?
myoglobin, because of its smaller size. Charge also has an effect to a lesser extent
Effect of charge on filtration in kidney
+ charged molecules filter more easily than - charged molecules. However, molecular size has a larger effect on filterability, so after a certain large molecular size, changes in charge will have no effect on filterability.
Index of filterability
ratio of the concentration of a given molecule in the filtrate (inside Bowman’s capsule) and in the plasma. Ratio of 1 indicates molecule passes through the filtration barrier easily
Do albumin and Hb has high or low index of filterability?
low, because they do not pass filtration barrier easily and mainly remain in the plasma
glomerular filtration rate (GFR)
volume of plasma filtered into Bowman’s capsule per unit time
formula for GFR
GFR = net filtration pressue (NFP) X filtration coefficient (kf)
equation for NFP
NFP = glomerular capillary hydraulic pressue (PGC) + Bowman’s capsule oncotic pressure (pieBC) - Bowman’s capsule hydraulic pressure (PBC) - glom. capillar oncotic pressure (pieGC)
main force moving fluid into Bowman’s capsule
hydrostatic pressure in glomerular capillary
5 factors that influence hydrostatic pressure of the glomerular capillary (PGC)
1) blood pressure
2) efferent and afferent arteriolar resistance
3) sympathetic nervous system
4) hormonal control
5) obstruction
higher PGC –> GFR?
increases
How does sympathetic system regulate GFR?
controls blood flow through the glomerular capillary bed and secondarily controls the hydrostatic pressure in glomerular capillaries
increased afferent arteriolar resistance –> PGC? GFR?
decreases both
increased efferent arteriolar resistance –> PGC and GFR?
increases both (pressure backs up in the system like a blocked hose)
normal GFR for dogs
80ml/min
what controls the filtration coefficient Kf? (2 main factors)
permeability and surface area for filtration
What happens to GFR as filtration coefficient Kf continues to increase?
GFR will increase rapidly at first, then reach a plateau as additional increases in Kf don’t have any effect on GFR
How can surface area for filtration be changed?
by controlling the number of glomerular capillaries that are perfused
starvation –> oncotic pressure of glom. capillary? GFR?
oncotic pressure drops due to decreased plasma protein concentrations. GFR rises
cellular debris in renal tubules –> GFR, urine flow?
both decrease. GFR decreases because high pressure in bladder raises pressure in ureters up to the kidney, causing resistance to filtration.
clearance
volume of plasma from which a substance is completely removed per unit time. Used to assess overall renal function
equation for renal clearance Cx
Cx = (Ux*V)/Px where Ux is conc. in urine, V is urine flow rate, and Px is conc. in plasma
inulin and its important properties
synthetic substance used as a tool to study renal clearance. clearance of inulin is a marker for GFR
- freely filtered
- not reabsorbed, secreted, produced, or metabolized by the kidney
- doesn’t alter GFR itself
GFR = Cin = (Uin*V)/Pin
GFR
clinical relevance of creatinine with respect to kidney
used as an indicator of GFR because plasma creatinine is inversely correlated with GFR
