Lecture 31: Glomerular function

Question 1

How much of our cardiac output do the kidneys receive

Answer 1

20% or 1/5

Because they need to filter the blood. Decreased flow = decreased filtration

Question 2

What are the driving forces of hydrostatic pressures

Answer 2

Hydrostatic pressures

Question 3

Explain colloid osmotic pressure

Answer 3

Large proteins act like water magnets. This means wherever proteins are it creates a colloid osmotic pressure pulling water towards themselves

Question 4

What are the positive pressures (favor filtration) in the glomerular capsule

Answer 4

Water in plasma (Glomerular hydrostatic pressure)
Protein in capsule (capsular colloid osmotic pressure)

Question 5

What are the negative pressures (favor filtration) in the glomerular capsule

Answer 5

Water in capsule (Capsular hydrostatic pressure)
Protein in plasma (Blood colloid osmotic pressure)

Question 6

What is net filtration pressure in the glomerular capsule

Answer 6

10mmHg

Question 7

What is the filtration fraction

Answer 7

The amount of plasma which is filtered through the glomeruli into the nephrons

20% or 1/5

Question 8

What is the Glomerular filtration rate

Answer 8

The amount of plasma filtered per minute (or day) by the kidneys.

Renal plasma flow (RPF) x Filtration Fraction
626mL/min x 20%

=125mL/min or 180L/day

Question 9

What is the renal filtered load

Answer 9

the amount of a particular substance (solute) in the plasma is filtered per unit of time

Question 10

How much blood (and plasma) do the kidneys receive?

Answer 10

Renal Blood Flow
Renal plasma flow

Question 11

What proportion of the plasma which enters the kidneys (renal plasma flow) is filtered

Answer 11

Filtered fraction (20% of renal plasma flow)

Question 12

How much plasma is filtered per minute?

Answer 12

Glomerular Filtration rate (125mL/min)

Question 13

How much of a substance in the plasma is filtered per minute?

Answer 13

Renal filtered load

Question 14

What is Renal Clearance

Answer 14

Clearance is the volume (mL) of plasma that is cleared of a substance by the kidneys per unit time (per minute)

Question 15

What substance can be used to estimate Glomerular Filtration Rate using Renal Clearance

Answer 15

Creatinine: A waste product produced by muscles already in the body

Can be measured in the blood and in the urine

also
Inulin: A polysaccharide that is not metabolised in the body and thus must be injected

Question 16

What substance can be used to estimate Renal Plasma fluid using Renal Clearance

Answer 16

We need a substance that needs to all be filtered and/or secreted into the tubule. NOT be reabsored from the tubule

This means that all of the plasma that passes through the kidneys each minute will be cleared of the substance: renal plasma flow (RPF)

PAH is a small molecule that meets these requirements but must be injected in