Renal Clearance Flashcards Preview

Human Function- Exam 4 Material > Renal Clearance > Flashcards

Flashcards in Renal Clearance Deck (20):
1

what is clearance?

the volume of plasm cleared of a substance by the kidney in a unit of time
amount excreted / plasma concentration
Cx = (Ux*V)/Px

2

what are characteristics of GFR markers?

- freely filtered (filtrate conc = plasma conc)
- neither reabsorbed or secreted
- not metabolized by cells
- accurately measureable

3

what are common GFR markers?

inulin
creatinin
cystatin C--NOT present in urine- degraded in tubules

4

what is the filtered amount?

GFR * plasma conc = filtered load

5

what is the definition of kidney failure in terms of GFR?

<25% of normal GFR

6

what is a draw back of using creatinine to measure GFR?

cannot detect acute renal failure because of a lag in measurements

7

what affects creatinine?

aging- decrease GFR
pregnancy- increase GFR
body composition- muscle mass present

8

what is fractional clearance?

ratio of substance clearance to inulin clearance

9

what is the fraction clearance of a GFR marker?

Cx / Cin = 1

10

what is the fractional clearance of a secreted substance?

Cx/ Cin > 1

11

what is the fractional clearance of an absorbed substance?

Cx / Cin < 1

12

what is tm? what substances have it?

saturation level of an organic substances- determined by the number of transporters present

13

what is PAH? what is it used for?

para-aminohippurate
used to measure renal plasma flow
Cpah = total RPF

14

what is the Fick method of renal plasma flow? why is it different?

takes into account the extraction efficiency for PAH
divides Upah * V by the difference in afferent and efferent arteriole concentrations of the substance (rather than plasma concentration)

15

how is the amount of water absorbed in the tubules determined?

U/P ratio for inulin
U/P = 1 no water reabsorption
U/P = 2 50% water absorbed
U/P = 100 99% of water reabsorbed

16

what is the percent of water reabsorbed?

100 - [100/(U/P)in]

17

what is the normal range of water reabsorption?

U/P = 50-100
(1% of filtered water is excreted)

18

what is free water clearance?

volume of plasma completely cleared of our water per unit time
CH2O = V - Cosm
Cosm = Uosm * V / Posm

19

what is positive free water clearance?

urine is hyposmotic
remaining body fluids are concentrated

20

what is negative free water clearance?

urine is hyperosmotic
remaining body fluids are diluted