3 Renal Clearance

Question 1

GFR gives a rough measure of the number of ___________.

Answer 1

Functioning nephrons

Question 2

Decreased GFR is a key sign of ___________.

Answer 2

Renal disease

Question 3

A reduction in GFR may indicate a disease ______________, or development of a ____________ disease.

Answer 3

progression; reversible

Question 4

GFR determines the ___________ of chronic renal insuficiency and _______ doses of drugs secreted by kidneys.

Answer 4

Grading; dosages

Question 5

ERx = ? (formula)

Answer 5

ERx = FLx + Sx - Rx

Question 6

If Rx and Sx = 0, then __________.

Answer 6

Erx = FLx

Question 7

FLx = ? (formula)

Answer 7

FLx = (GFR)(Px)

Question 8

Conservation of mass formula: GFR = ?

Answer 8

GFR = (Ux)(V)/Px (“UV over P”)

Question 9

The polusaccharide _______ is the gold standard GFR marker for measuring GFR, but is rarely used.

Answer 9

Inulin (inulin clearance = GFR)

Question 10

_____________ and _____________ are frequently used as indicators of GFR in practice

Answer 10

creatinine clearance; plasma creatinine concentration

Question 11

Why use creatinine to measure GFR?

Answer 11

1. Produced at constant rate
2. Freely filtered, not reabsorbed, and only slightly excreted
3. It’s already at steady state in blood if formation and excretion are stable
4. It can provide an estimate of GFR over the preceding hours

Question 12

2 ways to use creatinine to estimate GFR

Answer 12

1. Calculate creatinine clearance (Ccr) = GFR 2. Use Pcr to estimate GFR using a standard

Question 13

What is the normal BUN range?

Answer 13

9-18 mg/dL

Question 14

About ______ (fraction) of the filtered urea is reabsorbed.

Answer 14

1/2 (reabsorption increases when GFR is low)

Question 15

Why is urea a bad GFR marker?

Answer 15

Because about 1/2 of it gets reabsorbed

Question 16

BUN:Cr ratio should be ________

Answer 16

10 - 15

Question 17

BUN is more sensitive to _________ than _________.

Answer 17

↓ GFR; plasma Cr

Question 18

A high BUN:Cr occurs with _____________ (2)

Answer 18

Dehydration (↓ GFR) or upper GI bleed

Question 19

A normal BUN:Cr occurs with _____________ (2)

Answer 19

Acute tubular necrosis, loss of nephrons

Question 20

A low BUN:Cr ratio occurs with _____________ (3)

Answer 20

1. Severe skeletal muscle injury (↑ Cr) 2. Liver disease (↓ BUN) 3. Malnutrition (↓ BUN)

Question 21

Clearance equation:

Answer 21

Cx = (Ux)(V)/Px

Question 22

Clearance represents the ________ of plasma that is cleared of solute X per ________.

Answer 22

volume; minute

Question 23

Normal Cr clearance (=GFR) for females? For males?

Answer 23

females: 85-125 ml/min males: 97-140 ml/min (males clear faster than females)

Question 24

Clearance of a secreted substance will be _________ than Ccr, thus ________ than GFR.

Answer 24

greater; greater (creatinine is not reabsorbed and is only slightly secreted)

Question 25

Clearance of reabsorbed substances will be __________ than Ccr and _______ than GFR.

Answer 25

Less; less (if it’s reabsorbed there will be less being cleared) (Ex: Glucose is completely reabsorbed –> clearance is zero)

Question 26

How to tell if a substance is being reabsorbed or excreted?

Answer 26

Calculate clearance and compare it to GFR (If less than GFR, it’s reabsorbed…..If more than GFR, it’s excreted)

Question 27

All filtered glucose is _____________ by the kidney

Answer 27

reabsorbed

Question 28

Inulin clearance ratio = _________

Answer 28

Cx / C(inulin)

Question 29

If inulin clearance ratio = 1? < 1? >1?

Answer 29

ratio = 1: it mmust also be a GRF marker (filtered, but neither secereted nor reabsorbed)

ratio < 1: It’s either not filtered, or it is filtered and reabsorbed

ratio > 1: it’s filtered and secreted

Question 30

__________ is an estimate of RPF, because all the blood is cleared of it.

Answer 30

Para-aminohippurate (PAH)

Some is filtered and the rest is excreted in urine (no PAH left in plasma leaving kidney)

Question 31

Use PAH and RPF to estimate RBF

Answer 31

Get effective RPF from Ppah, then RPF/(1-Hct) = RBF