Lecture 7 - Renal Clearance

Question 1

Define flow rate?

Answer 1

feed of fluid in ml/min

Question 2

What is GFR?

Answer 2

glomerular filtration rate - amount of fluid going into bowman’s capsule per unit of time.

Question 3

What is usually the normal GFR?

Answer 3

100-130 ml/min

Question 4

using GFR we can estimate what?

Answer 4

we can estimate the amount of dissolves molecules of electrolytes, glucose and amino acids that are entering bowmans capsule.

It is not universally true, for example we can’t calculate glucose, only specific molecules. Like inulin (fructose polymer) we inject it in, and its not normally present in the body.

Question 5

normal urine flow rate?

Answer 5

1-3 ml/min

Question 6

Explain each variable?

Answer 6

TL - Tubular load which is the amount of solute delivered into the tubule

Ps - Plasma concentration

GFR - Glomerular filtration rate

Question 7

Why isn’t TL necesarrily high just because Ps is high?

Answer 7

because of filtration rate, therefore only molecules that are freely filtired would be true for this.

Question 8

WHat is Tm or transport max?

Answer 8

essentially when transporters are shuttling solutes, the rate of shuttling has a maximum

Question 9

What happens when solutes present (Tl) exceed the amount that can be transported (Tm)?

Answer 9

You pee it out, it will show up in the urine

Question 10

When one nephron reaches its transport maximum what happens?

Answer 10

tiny amounts of the solutes will appeak in the urine.

Question 11

As more nephrons reach their transport maximum, ……… appears in the urine

Answer 11

more solute

Question 12

What is threshold?

Answer 12

Appearance of solute in the urine before you reach the overall Tm of the kidney.. Essentially, the plasma concentration at which a substance begins to appear in the urine.

Question 13

What is the benefit and negative of measure renal clearnace?

Answer 13

measure both left and right at the same time.

Measures the ability of the kidney to handle solutes and water.

Question 14

What is renal clearance?

Answer 14

Compares the filtration rate of a substance to the rate of its appearance in the urine. Essentially the amount filitred vs the amount excreted.

Question 15

Why is renal clearance limited?

Answer 15

Measure all nephrons at once and so we cannot give info on specific regions of the nephron or on individual nepherons.

Question 16

the clearance value of a certain substance is the ……. which is cleared of this substance by the kidney into urine.

Answer 16

volume of plasma

Question 17

In order to measure renal clearance we need to measure what?

Answer 17

V - volume of urine

U - concentration of substance in urine

P - concentration of substance in plasma

Question 18

What is the maximum and minumum concentration in the plasma?

Answer 18

min - 0

max - 600-750

Question 19

What can we use renal clearance for ?

Answer 19

• measurement of glomerular filtration rate
• measurement of the renal plasma flow rate (from thre renal blood flow rate )
• Determine the renal handling of the different substances, whether or not the substance is reabsorbed or secreted by the renal tubules.

Question 20

A = V + U

Answer 20

Arterial input (amount going in) = Venous output + urine output

Question 21

What is the formula for clearance?

Answer 21

C = (U X V) / P

c- clearance

u - urine output

v - venous output

p - plasma concetration

Question 22

What is the clearance of PAH and why?

Answer 22

It is 100 % cleared beause it is freely filtered, not metabolises, not reabsorbed and freely secreted.

Question 23

What is the clearance of inulin and why?

Answer 23

Filtration rate = excretion rate

because it is freely filtered, not metabolised, not reabsorbed and not secreted.

fully excreted

Question 24

What is inulin used for?

Answer 24

used experimentally to measure GFR

Question 25

What is creatinine used for and what does it indicate?

Answer 25

It is secreted to a small extent about only 10 % and so an elevated Pcr is an indicator of reduced GFR.

Question 26

What does Clearence of over and under 125 mean?

Answer 26

over - reabsorption

under - secretion