gfr & renal clearance

Question 1

What units should renal clearance be in?

Answer 1

mL/min

Question 2

Renal clearance of

• Albumin
• Glucose
• Na⁺, urea, phosphate, Cl-

Answer 2

• Albumin = 0 (never crosses capillary)
• Glucose = 0 (filtered, but completely reabsorbed)
• Na, urea, phosphate, Cl have positive renal clearances because they’re filtered and partially reabsorbed

Question 3

Which clearance represents the GFR and why?

Answer 3

• Inulin is freely filtered, but neither reabsorbed or secreted
  
  • Inulin filtered = Inulin in the urine
• Glomerular marker: its clearance = GFR

Question 4

Which clearance is used to measure renal plasma flow and why?

Answer 4

PAH has the highest clerance because they’re both filtered and secreted from the renal arterial blood.

PAH entering the kidney = PAH in the urine.

Question 5

Describe the reabsorption of water, sodium, and glucose vs urea

Answer 5

99-100% of water, sodium, and glucose get reabsorbed, but

less than half of urea gets reabsorbed.

Question 6

GFR equation using inulin

Answer 6

Since inulin filtered = inulin excreted,

Inulin filtered = (GFR)[Inulin_plasma]

Inulin excreted = (Urine flow)[Inulin_urine]

Question 7

Creatinine & GFR

Answer 7

• Creatinine is an endogenous substance that is almost as good a glomerular marker as inulin , meaning its filtration and its excretion are ~equal.
• GFR would have to decline ALOT before plasma creatinine increases.
  
  • Ex) In kidney failure/donation, GFR drops enough such that the body doubles [Cr]_plasma (it’s not gettin filtered)

Question 8

What does it say about GFR if plasma [creatinine] has been increased from 1mg/dL to 2? to 4?

Answer 8

If [creatinine]_plasma doubled, then GFR must have been 50%.

If [creatinine]_plasma quartered, then GFR must have been 25%

Question 9

Filtered load

What is it and whats the eqn?

Answer 9

The amount of substance filtered into Bowman’s space.

Filtered load = (GFR) [P_x]

Question 10

What should GFR be?

Answer 10

90 mL/min or higher

Question 11

Excretion rate eqn

Answer 11

Excretion rate = (V) [U]x

where V = urine flow rate

Question 12

If the clearance of substance X is less than the clearance of inulin,

Answer 12

If the clearance of substance X is less than GFR (the clerance of inulin), then that substance underwent reabsorption

Question 13

If the clearance of X is greater than the clerance of inulin, that means that substance X…

Answer 13

If clerance of X is greater than GFR, then that means the substance underwent secretion

Question 14

Net reabsorption of X =

Answer 14

Filtered load_X - Excretion_X

Question 15

Fractional excretion of X =

Answer 15

Excretion_X / Filtered load_X

Question 16

filtration fraction =

Answer 16

GFR / RPF

Question 17

Renal blood flow (RBF) =

Answer 17

RPF / (1-hematocrit ratio)

E.g. if Hematocrit is 40, hematocrit ratio is .4

Question 18

Prostaglandins work on the __ arteriole

RAS works on the ___ arteriole

Answer 18

Prostaglandins, kinins, dopamine, ANP, and NO all work on the afferent arteriole

Angiotensin II, nor adrenaline, endothelin, and ADH work on the efferent arteriole