5.1.2: Excretion

Question 1

What is the term for blood with too low a water potential?

Answer 1

Hypertonic

Hypertonic conditions can occur due to loss of water from sweating or not drinking enough water.

Question 2

What is the corrective mechanism when blood is hypertonic?

Answer 2

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

This results in more concentrated urine.

Question 3

What is the term for blood with too high a water potential?

Answer 3

Hypotonic

Hypotonic conditions can occur due to drinking too much water or a lack of ions in the diet.

Question 4

What happens to water reabsorption when blood is hypotonic?

Answer 4

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

This results in more dilute urine.

Question 5

Where are osmoreceptors located?

Answer 5

In the hypothalamus

Osmoreceptors detect changes in the water potential of the blood.

Question 6

What hormone is produced in the hypothalamus?

Answer 6

Antidiuretic hormone (ADH)

ADH is crucial for regulating water reabsorption in the kidneys.

Question 7

Where does ADH travel after being produced in the hypothalamus?

Answer 7

To the posterior pituitary gland

From there, ADH is released into the bloodstream.

Question 8

What occurs when the water potential of the blood is too low?

Answer 8

Osmoreceptors shrivel and stimulate the hypothalamus to produce more ADH

This increases water reabsorption in the kidneys.

Question 9

What effect does ADH have on the kidney?

Answer 9

Increases the permeability of the walls of the collecting duct and distal convoluted tubule to water

This leads to more water being reabsorbed into the blood.

Question 10

What are aquaporins?

Answer 10

Channel proteins that allow water to be transported across the membrane

They increase the permeability of the membrane to water.

Question 11

What activates the insertion of aquaporin vesicles into the membrane?

Answer 11

Binding of ADH to complementary receptors on target cells

This activates adenyl cyclase to produce cAMP.

Question 12

What is the role of cAMP in the action of ADH?

Answer 12

Activates an enzyme that causes vesicles containing aquaporins to fuse with the membrane

This enhances water reabsorption in the kidneys.

Question 13

Fill in the blank: The collecting duct and distal convoluted tubule become more permeable to water due to the action of _______.

Answer 13

ADH

Question 14

True or False: ADH decreases water reabsorption when blood is hypotonic.

Answer 14

True