6C Controlling Blood Water Potential

Question 1

Define osmoregulation

Answer 1

Controlling blood water potential

Question 2

What happens if blood water potential is too low

Answer 2

more water is reabsorbed by osmosis into the blood from the tubules of the nephrons

This means the urine is more concentrated so less water is lost during excretion

Question 3

What happens if blood water potential is too high

Answer 3

less water is reabsorbed by osmosis into the blood from the tubules of the nephrons

This means the urine is more dilute so more water is lost during excretion

Question 4

Functions of the limbs in the loop of Henle

Answer 4

they control the movement of sodium ions so that water can be reabsorbed by the blood

Question 5

Process of the loop of Henle limbs maintaining a sodium ion gradient

Answer 5

Near the top of the ascending limb Na+ ions are pumped out into the medulla via active transport. The ascending limb is impermeable to water so the water stays inside the tubule. This creates a low water potential in the medulla because there is a high ion concentration of ions

Due to the lower water potential in the medulla water moves out of the descending limb into the medulla by osmosis. This makes the filtrate more concentrated . The water in the medulla is reabsorbed into the blood through the capillary network

Near the bottom of the ascending limb Na+ ions diffuse out into the medulla which lowers the water potential further in the medulla. The ascending limb is impermeable to water so it stays in the tubule

Water moves out of the distal convoluted tubule by osmosis and is reabsorbed into the blood

The first three stages massively increase the ion concentration in the medulla which lowers the water potential. This causes water to move out of collecting duct by osmosis . As before the water in the medulla is reabsorbed into the blood through the capillary network

Question 6

How is the water potential of the blood monitored

Answer 6

by osmoreceptors in the hypothalamus when the water potential decreases water will move out of the osmoreceptors by osmosis causing the cells to decrease in volume . This sends a signal to the hypothalamus which sends a signal to the posterior pituitary gland to release ADH into the blood

Question 7

Why does ADH level rise when you are dehydrated

Answer 7

The water content of the blood drops, so it’s water potential drops
This is detected by osmoreceptors in the hypothalamus
The posterior pituitary gland is stimulated to release more ADH into the blood
More ADH means the DTC and the collecting duct become more permeable so more water is reabsorbed into the blood by osmosis
A small amount of highly concentrated urine is produced and less water is lost

Question 8

Why does ADH level fall when you are hydrated

Answer 8

The water content of the blood rises, so it’s water potential rises
This is detected by osmoreceptors in the hypothalamus
The posterior pituitary gland is stimulated to release less ADH into the blood
Less ADH means the DTC and the collecting duct become less permeable so less water is reabsorbed into the blood by osmosis
A large amount of dilute urine is produced and more water is lost