Sarah Nephron

Question 1

Describe ultrafiltration

Answer 1

Due to high pressure - caused by contraction of heart and afferent arteriole is wider then the efferent arteriole

Forces molecules out of the capillary and to the basement membrane which acts as a fine filter.

It only allows molecules of less then 70000 Mr to pass through = renal threshold

Then molecules pass between the gaps in the podocyte into renal capsule to form glomerular filtrate

Question 2

Describe selective reabsorption in the PCT

Answer 2

80% of molecules go back into the blood (reabsorb)

100% of glucose is selectively reabsorbed in a healthy person by active transport using carrier proteins

Question 3

Why does a diabetic person have glucose in their urine?

Answer 3

High blood glucose levels

So get high glucose levels in glomerular filtrate

All the carrier proteins in the PCT are saturated so not all of the glucose can be reabsorbed so some remains in the filtrate which then forms urine

Question 4

Describe the loop of henle

Answer 4

The descending limb is permeable to water and impermeable to Na+

1. Water moves out by osmosis down a water potential gradient
2. As water is lost from descending limb the filtrate becomes more concentrated

At the base of the loop of henle this is wear it’s most concentrated

The descending limb is impermeable to water and permeable to Na+

1. Na+ actively moved out of ascending limb, this creates a salt bath which lowers water potential and maintains a water potential gradient along the length of the descending limb of the loop of henle to ensure water moves out across entire length

Question 5

Why do desert rats have a longer loop of henle then beavers

Answer 5

Longer loop of henle in animals that live in dry conditions to maximise water reabsorption and help conserve water

Question 6

Describe osmoregulation (DCT and collecting duct) if water potential is too high

Answer 6

1. Osmoreceptors in hypothalamus detects water potential of blood
2. No/less ADH released from pituitary
3. Decrease in permeability of DCT and collecting duct
4. Less water reabsorbed into blood
5. Large volume of urine and more dilute urine

Question 7

Describe osmoregulation (DCT and collecting duct) if water potential is too low

Answer 7

Osmoreceptors in hypothalamus detects water potential of blood

ADH released form pituitary gland

ADH increases permeability of DCT/CD by increasing aquaporins in the cell membranes

More water reabsorbed into blood

More concentrated urine and less volume of urine