RBF & GFR DSA

Question 1

What are the three layers of the glomerular filtration barrier

Answer 1

capillary endothelium
glomerular basement membrane
podocyte epithelium

Question 2

What cell adhesion molecules block large proteins in the filtration slit?

Answer 2

nephrin

Question 3

How does the glycocalyx contribute to filtration?

Answer 3

the glycocalyx is negatively charged and therefore repels anionic proteins

Question 4

What histological findings are consistent with a damaged filtration barrier

Answer 4

glomerular sclerosis
hypercellularity
thickened basement membrane

Question 5

How do you calculate filtered load

Answer 5

[X] in plasma*GFR

Question 6

calculate urinary excretion

Answer 6

urinary excretion = amount filtered - amount reabsorbed + amount secreted

Question 7

calculate tubular reabsorption

Answer 7

tubular reabsorption = glomerular filtration - urinary excretion + amount secreted

Question 8

equation for urine flow rate

Answer 8

urine volume/time

Question 9

equation for urinary concentration

Answer 9

concentration/volume

Question 10

equation for urine excretion rate

Answer 10

x = Ux*V

Question 11

renal clearance

Answer 11

rate of removal by the kidneys

Ux*V)/(Px

Question 12

define GFR and average value

Answer 12

volume of plasma filtered in the combined nephrons of both kidneys per unit time
20% RBF / 125mL/minute

Question 13

equation for filtration fraction

Answer 13

FF=GFR/RBF

Question 14

What happens to oncotic pressure of the efferent arteriole as FF increases and why?

Answer 14

Oncotic pressure increases bc more blood is being filtered out, leaving a higher [protein]

Question 15

What can cause decreased renal blood flow? What effect does this have on filtration factor?

Answer 15

renal artery stenosis, hemorrhage

increased FF

Question 16

equation for filtered load

Answer 16

GFR*Px

Question 17

equation for excretion

Answer 17

V*Ux

Question 18

equation for reabsorption

Answer 18

filtered load-excretion

Question 19

equation for the percentage of x reabsorbed per day

Answer 19

reabsorption/filtered load

Question 20

What is inulin and why is it useful?

Answer 20

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

Question 21

What does the SNS stimulate the juxtaglomerular cells to do & via what receptors?

Answer 21

renin, aldosterone, angiotensin II system

B1 adrenergic receptors

Question 22

What affect on a1 receptors in the kidney does the SNS system have?

Answer 22

vasoconstriction of the afferent (& less so, efferent) arterioles
increased Na+ absorption

Question 23

How are [plasma creatinine] and GFR related

Answer 23

They are inversely proportional

Question 24

What does an elevated BUN:creatinine ratio indicate?

Answer 24

A pre-renal issue - hypovolemia, dehydration, reduced renal perfusion, high protein diet

Question 25

What does a decreased BUN:creatinine ratio indicate?

Answer 25

renal disease - reduction of BUN reabsorption - liver disease, low protein diet

Question 26

Why can PAH be used to estimate renal plasma flow?

Answer 26

it is freely filtered - amount in renal artery is about equal to that excreted in urine