Renal Plasma Clearance

Question 1

What type of substance do you need to measure GFR?

Answer 1

Only filtered not reabsorbed or secreted

Question 2

What is inulin?

Answer 2

Inert polysaccharide that filters freely through the glomerular membrane

Question 3

Why is inulin good for measuring GFR?

Answer 3

Not naturally produced so you can inject a specific amount and know exactly how much is in there

Question 4

What is the formula for rate of inulin filtration?

Answer 4

[plasma inulin] x GFR

Question 5

What is renal clearance?

Answer 5

Volume of plasma completely cleared of the substance by kidney per unit time

Question 6

What are the cons of the inulin method?

Answer 6

Prolonged infusion and repeated plasma samples which make it hard for routine clinical use

Question 7

What are the advantages of the creatinine method?

Answer 7

It’s intrinsic and inert, released at a relatively steady level in plasma from skeletal muscle, no infusion needed, freely filtered and not reabsorbed in the tubule

Question 8

What are the disadvantages of the creatinine method?

Answer 8

Some is secreted in the tubule so it’s slightly wrong

Question 9

How is creatinine made?

Answer 9

Starts as creatine in the liver or diet and then is metabolised into creatinine in the muscle

Question 10

How does trimethoprim work?

Answer 10

Competes with creatinine for transporters that secrete it from blood into urine

Question 11

What does trimethoprim do?

Answer 11

Increase serum levels of creatinine

Question 12

What causes GFR decline?

Answer 12

Age and sex

Question 13

What are the two equations for estimating GFR?

Answer 13

MDRD and CRD-EPI

Question 14

Why doesnt CKD-EPI require weight?

Answer 14

Results are normalised to any surface area

Question 15

Why is the CDK-EPI more accurate than the MDRD?

Answer 15

Less biased as it accepts its limitations at the higher GFR

Question 16

How many stages of chronic kidney disease are there?

Answer 16

6- 1, 2, 3a, 3b, 4, 5

Question 17

What group of people is the eGFR inaccurate for?

Answer 17

People with extreme body types (malnourished, obese, amputees)

Question 18

When is the eGFR not valid?

Answer 18

Pregnant women or children

Question 19

What groups of people was the MDRD originally validated on?

Answer 19

US white and black patients

Question 20

What happens to substances with clearance < inulin?

Answer 20

Either not filtered freely or reabsorbed from tubule

Question 21

What happens to substances with clearance> inulin?

Answer 21

Secreted into tubule

Question 22

What happens when the clearance < GFR?

Answer 22

It’s not freely filtered and reabsorbed

Question 23

What happens when clearance > GFR?

Answer 23

Substances that are secreted

Question 24

What are some examples of clearance > GFR molecules?

Answer 24

Endogenous and exogenous

Question 25

Give an example of an endogenous substance

Answer 25

Weak organic acids and bases, adrenaline, dopamine and steroids

Question 26

Give an example of an exogenous substance

Answer 26

Penicillin, probenecia, para-aminohippuric acid

Question 27

What is renal plasma flow?

Answer 27

Rate at which plasma flows through the kidney

Question 28

What does renal plasma flow allow us to estimate?

Answer 28

The total blood flow through the kidneys

Question 29

What % of blood is plasma?

Answer 29

55

Question 30

What is para-aminohippuric acid?

Answer 30

Weak acidic metabolite of glycine

Question 31

Where and how is para-aminohippuric acid secreted?

Answer 31

Active transport occurs in the basolateral membrane and passive transport across luminal membrane into tubule

Question 32

What happens if plasma [PAH] is low enough?

Answer 32

It is completely cleared in a single pass thought the kidney

Question 33

What does PAH clearance = ?

Answer 33

Renal plasma flow

Question 34

What can be used to calculate the filtration fraction?

Answer 34

GFR and RPF

Question 35

What is the filtration fraction?

Answer 35

Fraction of plasma filtered through the glomerulus