RBF & GFR DSA Flashcards
What are the three layers of the glomerular filtration barrier
capillary endothelium
glomerular basement membrane
podocyte epithelium
What cell adhesion molecules block large proteins in the filtration slit?
nephrin
How does the glycocalyx contribute to filtration?
the glycocalyx is negatively charged and therefore repels anionic proteins
What histological findings are consistent with a damaged filtration barrier
glomerular sclerosis
hypercellularity
thickened basement membrane
How do you calculate filtered load
[X] in plasma*GFR
calculate urinary excretion
urinary excretion = amount filtered - amount reabsorbed + amount secreted
calculate tubular reabsorption
tubular reabsorption = glomerular filtration - urinary excretion + amount secreted
equation for urine flow rate
urine volume/time
equation for urinary concentration
concentration/volume
equation for urine excretion rate
x = Ux*V
renal clearance
rate of removal by the kidneys
Ux*V)/(Px
define GFR and average value
volume of plasma filtered in the combined nephrons of both kidneys per unit time
20% RBF / 125mL/minute
equation for filtration fraction
FF=GFR/RBF
What happens to oncotic pressure of the efferent arteriole as FF increases and why?
Oncotic pressure increases bc more blood is being filtered out, leaving a higher [protein]
What can cause decreased renal blood flow? What effect does this have on filtration factor?
renal artery stenosis, hemorrhage
increased FF
equation for filtered load
GFR*Px
equation for excretion
V*Ux
equation for reabsorption
filtered load-excretion
equation for the percentage of x reabsorbed per day
reabsorption/filtered load
What is inulin and why is it useful?
Inulin is a compound that is freely filtered and neither absorbed nor secreted, therefore the amount excreted in urine is equal to the amount filtered in the glomeruli
used to estimate GFR
What does the SNS stimulate the juxtaglomerular cells to do & via what receptors?
renin, aldosterone, angiotensin II system
B1 adrenergic receptors
What affect on a1 receptors in the kidney does the SNS system have?
vasoconstriction of the afferent (& less so, efferent) arterioles
increased Na+ absorption
How are [plasma creatinine] and GFR related
They are inversely proportional
What does an elevated BUN:creatinine ratio indicate?
A pre-renal issue - hypovolemia, dehydration, reduced renal perfusion, high protein diet
What does a decreased BUN:creatinine ratio indicate?
renal disease - reduction of BUN reabsorption - liver disease, low protein diet
Why can PAH be used to estimate renal plasma flow?
it is freely filtered - amount in renal artery is about equal to that excreted in urine
