Renal plasma clearance

Question 1

Favoring filtration

Answer 1

Glomerular capillary pressure (P GC) 60mmHg

Question 2

Opposing filtration

Answer 2

Hydrostatic pressure in bowman’s space (P BS) = 29 mmHg

Question 3

What is the osmotic force of the plasma proteins?

Answer 3

(pie GC) 29mmHg

Question 4

Net filtration pressure

Answer 4

P GC - P BS - Pie GC = 16 mmHg

Question 5

How often is plasma filtered?

Answer 5

60 x/day

Question 6

Rate of urine formation?

Answer 6

1 filtration
2 reabsorption
3 secretion
4 excretion

Question 7

Urinary excretion rate

Answer 7

GFR - reabsorption rate + secretion rate

Question 8

Why is GFR important?

Answer 8

GFR contributes to rapid removal of waste product

Question 9

What determines GFR?

Answer 9

Hydrostatic and oncotic pressures across capillary membranes

Permeability of capillary filtration barrier & surface area available

Question 10

How to measure GFR?

Answer 10

Not measured directly

Question 11

Inulin method

Answer 11

An inert polysaccharide, MW ~ 5,000
Filters freely through the glomerular membrane
Not absorbed, secreted or metabolized

Question 12

Equation for Inulin

Answer 12

Pin x GFR = Uin xV*

Question 13

GFR

Answer 13

Glomerular filtration rate ml.min -1

Question 14

Pin

Answer 14

Plasma inulin concentration; mg.ml-1

Question 15

Uin

Answer 15

Urine inulin concentration; mg.ml-1

Question 16

V*

Answer 16

Urine flow rate; ml.min-1

Question 17

Renal clearance

Answer 17

Of a substance is the volume of plasma that is completely cleared of the substance by the kidney per unit of time (ml/min)

Question 18

Clearance

Answer 18

The volume of plasma cleared of substances in 1 min

Question 19

Clearance formula

Answer 19

Cs x Ps = Us x V*

Question 20

Cs

Answer 20

The clearance rate of substance (s)

Question 21

Ps

Answer 21

Plasma concentration of s

Question 22

Us

Answer 22

Urinary concentration of S

Question 23

V*

Answer 23

Urine flow rate

Question 24

Drawbacks of the inulin method

Answer 24

Prolonged infusion
Repeated plasma samples
Difficult routine clinical use

Question 25

Advantages of creatinine method

Answer 25

An intrinsic inert substance 
Released at - steady level in plasma from skeletal muscle 
No infusion needed 
Freely filtered 
Not reabsorbed in the tubules

Question 26

Disadvantages of creatinine method

Answer 26

Some secreted into the tubule

GFR < C cr = U cr x V*/Pcr

Question 27

Fact about creatinine method

Answer 27

Trimethoprim competes with Cm for same transporters that secrete Cm from tubular blood into urine - increase in serum levels of Cm

Question 28

Normal range of GFR

Answer 28

Women - 44-88 umol/L (90.5-1 mg/dL)
Men - 62-106 umol/L (0.7 - 1.2 mg/dL)

So make adjustments need to sex and weight

Question 29

eGFR

Answer 29

estimated Glomerular Filtration rate

Question 30

What is actively reabsorbed?

Answer 30

All amino acid s
Clearance = zero unless excess filtered 
Pathological conditions
Production of bence - jones protein in plasma
Ca 2+, Na+, PO4 2-, Mg2+

Question 31

Passively reabsorbed

Answer 31

Cl-, urea, some drug

Question 32

What is RPF?

Answer 32

Renal Plasma Flow
The rate at which plasma flows through the kidney
Blood consists of about 55% plasma and 45% cellular components

Question 33

Paramminohippuric acid

Answer 33

PAH weak acid found in horse urine

used as a marker to measure renal plasma flow

Question 34

PAH secretion

Answer 34

Active transport occurs in the basolateral membrane

Passive transport across the luminal membrane into the tubule

Question 35

Renal filtration fraction

Answer 35

GFR &RPF can be used to calculate the filtrate fraction
GFR/RPF