Intro to ARF and Clearance

Question 1

Starling equation for single nephron

what is single most dominant factor at nephron level?

driving force for filtration at glomeruli = ?

Answer 1

glomerular capillary hydrostatic pressure

driving force for filtration at the glomeruli = blood pressure where filtration occurs = glomerular capillary hydrostatic pressure

Question 2

2 forces that oppose filtration pressure =?

Answer 2

1) back pressure at Bowman’s capsule from filtrate flowing into narrow tubule = PT
2) oncotic pressure of blood from large proteins

Question 3

what is name of mechanism causing GFR and RBF to maintain relatively constant over wide range of MAP

Answer 3

myogenic mechanism

Question 4

What happens when incr MAP

What happens when decr MAP

Answer 4

1) incr MAP
2) afferent arteriole constricts to decr GFR and RBF towards normal

1) decr MAP
2) afferent arteriole DILATES to allow more blood flow, incr GFR and incr RBF towards normal

Question 5

what happens to afferent and efferent arteriole during hypovolemia

Answer 5

1) both afferent and efferent arterioles constrict for separate control of RBF and GFR

• -> RBF decr by afferent constriction
• -> GFR maintained by efferent constrict –> diverts RBF to be filtered

Question 6

endogenous compounds affect
1) afferent arterioles

2) efferent arterioles

Answer 6

1) prostaglandins and thromboxanes –> VASODILATION

2) angiotensin II = VASOCONSTRICTION

Question 7

effect of NSAIDS and ACE inhibitors on afferent and efferent arterioles?

Answer 7

NSAIDS = block COX, decr vasodilation at afferent arteriole

ACE inhibitor = block angiotensin II, less vasoconstriction at efferent arteriole

Question 8

Definition of GFR

Answer 8

rate at which certain portion of plasma enters glomerulus and filtered

Question 9

equation for GFR

Answer 9

GFR = (Ux x V) / Px

Px = plasma concentration of X
Ux = urinary concentration of X
V = urinary flow rate

Question 10

GFRC can be calculated using clearance ONLY IF MEET 3 CRITERIA

Answer 10

1. X is freely filtered at the glomerulus
2. X gets into the urine only by filtration (there is no secretion)
3. X cannot be removed from the urine (there is not reabsorption)

Question 11

Creatinine clearance (over/under estimate GFR)

Answer 11

overestimate due to secretion of creatinine

Question 12

Urea clearance (over/underestimate GFR)

Answer 12

underestimate due to reabsorption of urea

Question 13

Equation for Creatinine clearance

Cockroft and Gault formula

Answer 13

Creatinine Clearance = [(A) X (140-age)) X weight]/(72 X Serum creatinine)

A is 1.0 is the patient is male, and 0.85 if female. Weight is in kilograms and age in years.

Question 14

Equation for creatinine clearance

Answer 14

Creatinine Clearance = (Urine Creatinine X V)/Plasma Creatinine

V = urine flow rate (divide volume of 24 hr urine by 1440 minutes

Question 15

All estimates of GFR only valid when patients in ___

Answer 15

steady state. They cease to be valid when creatinine is changing.