Renal Physiology

Question 1

60-40-20 rule (% of body weight)

Answer 1

60% total body water
40% ICF
20% ECF

Question 2

How much of ECF is in plasma vs. interstitial volume

Answer 2

1/4 is in plasma (1/12 TBW)

3/4 is in interstitial (1/4 TBW)

Question 3

How to measure plasma volume

Answer 3

Radiolabeled albumin

Question 4

Measuring extracellular volume

Answer 4

Inulin

Question 5

How to volume measurements work@!????

Answer 5

??????

Question 6

What is the charge barrier

Answer 6

Fused basement membrane with heparan sulfate leads to negative charge barrier which prevents albuminuria.

Question 7

Renal Clearance formula

Answer 7

Cx=UxV/Px = volume of plasma from which the substance is completely cleared per unit time. So if the substance is not reabsorbed or secreted, this measurement of the clearance based on urine and plasma concentration with a known flow rate will give you the mount of volume clearance/min

Question 8

Renal clearance relation to GFR

Answer 8

If < GFR, net reabsorption of X, if > GFR, net secretion of X.

Question 9

Cx

Answer 9

Clearance of X (mL/min)

Question 10

Ux

Answer 10

urine concentration of X (mg/mL)

Question 11

Px

Answer 11

plasma concentration of X (mg/mL)

Question 12

V

Answer 12

urine flow rate (mL/min)

Question 13

Best way of measuring GFR

Answer 13

inulin: no reabs. or secretion

Question 14

Creatinine clearance and GFR

Answer 14

overestimates because it is secreted

Question 15

Measuring effective renal plasma flow

Answer 15

para-aminohippuric acid (PAH) clearance, nothing of it is left exiting the kidneys (filtered and actively secreted)

Question 16

fact: ERPF underestimates true renal plasma flow by 10%

Answer 16

.

Question 17

What is the filtration fraction

Answer 17

FF = GFR/RPF = normally around 20%

Question 18

Filtered load (mg/min)

Answer 18

GFR (mL/min) x plasma concentration (mg/mL)

Question 19

What do NSAIDs do

Answer 19

Decrease prostaglandins: constrict the afferent arteriole

Question 20

What do ACEIs do

Answer 20

Decrease AT II: dilates the efferent arteriole

Question 21

Why does increasing plasma concentration decrease GFR?

Answer 21

Inc. oncotic pressure in the capillaries.