I/E: Blood Water Potential

Question 1

Osmoregulation

Answer 1

The process of the kidneys regulating the water potential of the blood and urine.

Question 2

What happens if the water potential of the blood is too low?

Answer 2

• More water reabsorbed by osmosis into blood from tubules of nephrons.
• Urine is more concentrated, so less water is lost during excretion.

Question 3

What happens if the water potential of the blood is too high?

Question 4

Where is the loop of Henle located?

Answer 4

In medulla of the kidneys

Question 5

What is the loop of Henle made of?

What do these do?

Answer 5

Descending and ascending limb.

Control the movement of sodium ions so water can be reabsorbed by the blood.

Question 6

What happens at the top of the ascending limb?

Answer 6

Na+ ions are pumped out into medulla using active transport.

Question 7

What happens to water at the top of the ascending limb?

Answer 7

Water stays inside tubule as ascending limb in impermeable to water.

Question 8

Describe the water potential in the medulla:

What is this created by?

Answer 8

Low water potential - high concentration of ions.

• Na+ ions pumped in using active transport.*
• Water does not enter as ascending limb is impermeable.*

Question 9

Why is the filtrate more concentration in the descending limb?

Answer 9

Water moves out of descending limb - lower WP in medulla.

Ions can’t move out as descending limb isn’t permeable to them.

Question 10

What happens to the water in the medulla?

Answer 10

Reabsorbed into the blood through capillary network.

Question 11

Describe the permeability of the descending limb and ascending limb to:

• water?
• ions?

Answer 11

Descending limb = permeable to ions, impermeable to water.

Ascending limb = impermeable to ions, permeable to water.

Question 12

What happens near the bottom of the ascending limb?

Answer 12

Na+ ions diffuse into the medulla, further lowering water potential in medulla.

Water stays in tubules as limb is impermeable.

Question 13

What causes water to move out of the collecting duct by osmosis?

Answer 13

Higher ion concentration in medulla, which lowers the water potential.

Question 14

What causes an increased ion concentration in the medulla?

Answer 14

• Na+ ions pumped out at top of ascending limb by active transport.
• Water moves out of descending limb by osmosis.
• Na+ ions diffuse into meddula near the bottom of ascending limb.

Question 15

Describe the movement of water in the distal convoluted tubule:

Answer 15

Moves out by osmosis and reabsorbs into the blood.

Question 16

How does the loop of Henle maintain a sodium ion gradient?

Answer 16

• Lower WP in medulla causes water to move out of descending limb, making filtrate more concentrated.
• Water is reabsored into blood.
• Na+ ions diffuse into medulla at bottom of ascending limb, lowering WP in medulla.
• Na+ pumped into medulla using active transport at top of ascending limb.
• Ascending limb is impermeable to water, so WP in medulla remains low.

Question 17

What controls the volume of water reabsorbed into the capillaries?

Answer 17

Changing permeability of the DCT and collecting duct.

Question 18

Where are osmoreceptors found?

Answer 18

Hypothalamus

Question 19

What happens to osmoreceptors when WP of blood decreases?

Answer 19

• Water moves out of osmoreceptors by osmosis.
• Cells decrease in volume.
• Sends a signal to other cells in hypothalamus.
• Sends a signal to posterior pituitary gland.
• ADH is released into blood.

Question 20

What does ADH do?

Answer 20

Makes walls of DCT and collecting duct more permeable to water.

• Means more water is reabsorbed into medulla and blood by osmosis.
• Less water loss.

Question 21

What happens to blood ADH when you are dehydrated?

Answer 21

• Water content + WP of blood decreases.
• Detected by osmoreceptors in hypothalamus.
• Posterior pituitary gland is stimulared to release more ADH into blood.
• More ADH means DCT and collecting duct become more permeable, so more water is reabsorbed into blood by osmosis.
• Small amount of highly concentrated urine is produced and less water is lost.

Question 22

What happens to blood ADH when you are hydrated?

Answer 22

• Water content + WP of blood rises.
• Detected by osmoreceptors in hypothalamus.
• Posterior pituitary gland releases less ADH into the blood.
• Less ADH means that the DCT and collecting duct become less permeable, so less water is reabsorbed into the blood by osmosis.
• Large amount of dilute urine is produced and more water is lost.