Glomerular filtration

Question 1

How many layers are glomerular capillary membranes made up of?

Answer 1

Three

Question 2

What are the layers of the glomerular capillary membranes?

Answer 2

Endothelium

Basement membrane

Podocytes

Question 3

What type of endothelium do glomerular capillaries have?

Answer 3

Fenestrated, meaning they have holes between endothelial cells

Question 4

What is the basment membrane of the glomerular capillaries made up of?

Answer 4

Collagen fibres

Glycoproteins that are negatively charged

Question 5

What is the structure of podocytes?

Answer 5

Give off projections called pedicels

pedicels contain spaces in between them

Question 6

What are the spaces in between pedicels called?

Answer 6

Filtration slits

Question 7

What is glomerular filtration?

Answer 7

Refers to the process of fluid and molecules passing from the glomerular capillaries into Bowman’s capsule

Question 8

What do fluids and molecules pass through as they are filtered from the glomerular capillary into Bowman’s capsule?

Answer 8

Pass through fenestrations between cells in endothelial layer of glomerular capillary
then through gaps in basement membrane
then through filtration slits

Question 9

What factors determine whether an ion/small molecule can be filtered out of the glomerular capillaries into Bowman’s capsule?

Answer 9

Its size

Its charge

Question 10

How does size affect whether an ion/small molecule can be filtered out of the glomerular capillaries into Bowman’s capsule?

Answer 10

Large molecules are too big to pass through the glomerular capillary membrane
remain in the glomerular capillaries

Small molecules pass through the glomerular capillary membrane
into Bowman’s capsule

Question 11

How does charge affect whether an ion/small molecule can be filtered out of the glomerular capillaries into Bowman’s capsule?

Answer 11

Two molecules of the same size, one is positively charged and the other is negatively charged
more of the positively charged molecule passes through the glomerular capillary membrane into Bowman’s capsule
because the negatively charged molecule is repelled by the negatively charged glycoproteins in the basement membrane

Question 12

What is the glomerular filtrate?

Answer 12

Refers to the fluid and molecules themselves that leave the glomerular capillaries and pass into Bowman’s capsule

Question 13

What is the glomerular filtrate made up of?

Answer 13

Water

Ions

Small molecules e.g. gluose, amino acids, urea

Question 14

What are the concentrations of water, ions, small molecules etc. in the glomerular filtrate, compared to the plasma?

Answer 14

They are the same

Question 15

What parts of the blood do not form part of the glomerular filtrate?

Answer 15

Cells

Proteins e.g. albumin

Question 16

Why do cells and proteins e.g. albumin not form part of the glomerular filtrate?

Answer 16

They are too large to pass through the glomerular capillary membranes

Also proteins are negatively charged, so they are repelled by the negatively charged glycoproteins in the basement membrane of the glomerular capillaries

Question 17

What ion/small molecule does not have the same concentration in the glomerular filtrate as it does in the plasma? Why?

Answer 17

Calcium ions

Because of calcium binding proteins in the plasma holding on to it
and themselves not being filtered out

Question 18

What is proteinuria?

Answer 18

Proteins in the urine

Question 19

What is a cause of proteinuria to do with the glomerular capillary membrane?

Answer 19

Loss of negatively charges on glycoproteins in basement membrane
smaller negatively charged membranes can pass through glomerular capillary membrane

Question 20

What is meant by the filtration fraction?

Answer 20

The amount of renal plasma flow that is filtered out of the glomerular capillary into Bowman’s capsule

Question 21

What is the actual normal filtration fraction?

Answer 21

20%

Question 22

What is meant by glomerular filtration rate (GFR)?

Answer 22

The amount of fluid and molecules pass from the glomerular capillaries into Bowman’s capsule per unit time

Question 23

What is the actual normal GFR?

Answer 23

125ml/min

140-180L/day

Question 24

What are the factors of the GFR?

Answer 24

Hydrostatic and oncotic pressures of glomerular capillaries and Bowman’s capsule

Question 25

How does glomerular hydrostatic pressure affect the GFR?

Answer 25

Higher glomerular hydrostatic pressure
more fluid pushes out of the glomerular capillary into Bowman’s capsule
increases GFR

Question 26

How does glomerular hydrostatic pressure change across the length of the glomerular capillary? Why?

Answer 26

It decreases
because fluid is filtered out of the glomerular capillary into Bowman’s capsule
less fluid in glomerular capillary

Question 27

How does glomerular oncotic pressure affect the GFR?

Answer 27

Higher glomerular oncotic pressure
more force drawing water into the glomerular capillary from Bowman’s capsule
decreases GFR

Question 28

How does glomerular oncotic pressure change across the length of the glomerular capillary? Why?

Answer 28

It increases
because water is filtered out of the glomerular capillary into Bowman’s capsule, but proteins remain
become more concentrated

Question 29

How does Bowman’s capsule hydrostatic pressure affect the GFR?

Answer 29

Higher Bowman’s capsule hydrostatic pressure
more fluid pushing out of Bowman’s capsule into glomerular capillary
decreases GFR

Question 30

What pathological state can cause an increase in Bowman’s capsule hydrostatic pressure?

Answer 30

Obstruction of urinary tract by e.g. stone

Question 31

What is meant by the net filtration pressure?

Answer 31

The overall pressure gradient between the glomerular capillary and the Bowman’s capsule