The Kidney - Ultrafiltration

Question 1

What is the purpose of ultrafiltration

Answer 1

Filter small molecules (water, glucose, urea, amino acids etc) out of the blood capillaries of the glomeulus and into the Bowman’s capsule to form filtrate (glomerular filtrate)

Question 2

Where does ultrafiltration occur

Answer 2

Bowman’s capsule

Question 3

Structures needed for bowmans capsule to filtrate

Answer 3

Thin efferent connected to glomerulus (windy spirally section) connected to thick afferent
Surrounding glomerulus is the sieve basement membrane (podocytes) which is then surrounded by the bowman’s capsule

Question 4

How does blood travel during ultrafiltration

Answer 4

Blood enters glomerulus through afferent and exits through efferent

Question 5

Why is the bloodstream important in ultrafiltration

Answer 5

Blood streams forms pressure that pushes molecules through podocytes (sieve)
Blood pressure is therefore high in glomerular capillaries into Bowman’s capsule

Question 6

Water potential

Answer 6

Water potential high in glomerulus than of filtrate in Bowman’s capsule
Difference in water potential between plasma in glomerular capillaries allows filtrate to enter Bowman’s capsule

Question 7

What molecules do podocytes sieve out

Answer 7

H2O, amino acids, ions, glucose importantly

Question 8

What does the basement membrane separating the sieve and capillaries do

Answer 8

Prevents large proteins going through sieve
Made of glycoproteins and collagen

Question 9

How does ultrafiltration work

Answer 9

1) Thin capillaries increase pressure to force small molecules in between podocytes into the bowmans capsule.
2) Water potential increases in the blood plasma in the glomerular capillaries above water potential of the filtrate in the Bowmans capsule
3) Water moves down a water potential gradient from high to low, this water potential is increased by high pressure and lowered with presence of solutes

Question 10

The effect of pressure and the effect of solute

Answer 10

Solute concentration in the blood plasma of the capillaries is higher than that in the filtrate of the bowmans capsule
Water moves down a water potential gradient from the bowmans cap into the blood plasma in glomerular capillaries
The effect of pressure from blood capillaries overpowers the effect of the solute

Question 11

Mark scheme ultrafiltration occurs

Answer 11

1) High hydrostatic pressure
2) Glucose and water
3) Pass through pores in the endothelium
4) Through the basement membrane