The Kidney

Question 1

What is osmoregulation?

Answer 1

Where the kidneys regulate the water potential of the blood and urine so that the body has the right amount of water.

Question 2

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

Answer 2

The body is dehydrated so more water is reabsorbed by osmosis from the tubules of the nephron into the blood making the urine more concentrated so you don’t lose as much water during excretion

Question 3

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

Answer 3

The body is too hydrated so less water is reabsorbed into the blood by osmosis from the tubules in the nephron ans the urine is more dilute meaning more water is lost during excretion

Question 4

Where is water reabsorbed into the blood?

Answer 4

Along almost all of the nephron

Question 5

Where does regulation of water potential mainly take place?

Answer 5

loop of Henle, collecting duct and DCT (distal convoluted tubule)

Question 6

What controls the volume of water reabsorbed by the DCT and collecting duct?

Answer 6

hormones

Question 7

Where is the loops of Henle found?

Answer 7

In the medulla - the inner layer of the kidney

Question 8

What is the use of sodium ions in the reabsorption of water?

Answer 8

They help to establish a water potetential which drives the reabsorption of water from the glomerular filtrate back into the blood

Question 9

Describe the process of reabsorption in the loop of Henle.

Answer 9

Near top of ascending limb(AL), Na+ actively pumped out into the medulla, water remains in the tubule, this lowers the water potetional of the medulla.
Because the water potential is lower in the medulla than the descending limb(DL), water moves out of the DL into the medulla by osmosis - making the glomerular filtrate more concentrated as the ions cannot diffuse out of the DL as it isn’t permeable to them. Then the water in the medulla is reabsorbed into the blood through the capillary network.
Near the bottom of the AL, Na+ diffuse out into the medulla further lowering the water potential in the medulla.
Then water moves out of the DCT by osmosis and is reabsorbed into the blood
The first three stages massively increases the concentration of ions in the medulla which lowers the water potential –> causing water to move out of the collecting duct by osmosis
As before, the water is reabsorbed into the blood through the capillary network

Question 10

Describe the permeability to water of the ascending and descending limb?

Answer 10

The ascending limb in impermeable to water and the descending limb is permeable to water.

Question 11

What controls the volume of water being reabsorbed into the capillaries?

Answer 11

by changing the permeability of the DCT and the collecting duct

Question 12

What is the water potential of the blood monitored by?

Answer 12

Osmoreceptors

Question 14

Where are osmoreceptors found?

Answer 14

In the part of the brain called the hypothalamus

Question 14

What happens to the osmoreceptor cells when the water potential of the blood decreases?

Answer 14

Water moves out of the cells by osmosis so the osmoreceptor cells decrease in volume

Question 14

What does the decrease in osmoreceptor cell volume do?

Answer 14

Sends a signal to other cells in the hypothalamus which send a signal to the posterior pituitary gland causing the gland to release a hormone into the blood –> the antidiuretic hormone (ADH)

Question 15

What does ADH do?

Answer 15

Binds to receptors on the plasma membranes of cells in the DCT and collecting duct and when this happens, protein channels called aquaporins are inserted into the plasma membrane

Question 15

What do the protein channels - aquaporins do?

Answer 15

They allow water to pass through via osmosis and therefore make the walls of the collecting duct and the DCT more permeable to water MEANING that more water is reabsorbed into the medulla + blood from these tubules = a small amount of conc urine is produced meaning less water is lost from the body

Question 16

Describe what happens when water content is too high?

Answer 16

Water content of the blood rises, so blood water potential rises, detected by osmoreceptors in the hypothalamus, the posterior pituitary gland releases less ADH into the blood, so DCT and collecting are less permeable, a large amount of dilute urine is prodcued and more water is lost.

Question 16

Describe what happens when water content is too low?

Answer 16

Water content of the blood drops so lowers the blood water potential. Osmoreceptors decrease in volume as water moves out of them via osmosis, this sends a signal to other cells in the hypothalamus which send signals to the posterior pituitary gland which then releases ADH. The ADH binds to receptors on the plasma membranes of cells in the wall of the collecting duct and DCT and increases the permeability by adding protein channels called aquaporins so more water is reabsorbed into the blood by osmosis and a small amount of highly concentrated urine is lost - less water is lost