2.5.6: The function of the kidney 2

Question 1

What does the loop of Henle consist of?

Answer 1

• The loop of Henle consists of a descending limb that descends into the medulla and…
• an ascending limb that ascends back out to the cortex.

Question 2

The arrangement of the loop of Henle allows mineral ions (sodium and chlorine) to be transferred from the ascending limb to the descending limb. What is the overall effect?

Answer 2

• The overall effect is to increase the concentration of mineral ions in the tubule fluid…
• which has a similar effect on the concentration of mineral ions in the tissue fluid.
• This gives the water potential in the medulla a very low (very negative) water potential.

Question 3

What happens to the water potential in the descending limb as mineral ions enter the descending limb?

Answer 3

• The concentration of the fluid in the descending limb rises.
• This means that its water potential decreases (becomes more negative).

Question 4

How does the water potential in the descending limb change as the tubule descends into the medulla?

Answer 4

-It decreases (becomes increasingly more negative) the deeper the tubule descends into the medulla.

Question 5

As the fluid rises up the ascending limb, mineral ions leave the fluid. Which processes are used?

Answer 5

• At the base, this movement is by diffusion.
• Higher up the ascending limb active transport is used to move mineral ions out.
• The upper portion is also impermeable to water.

Question 6

What is the effect of these ionic movements?

Answer 6

• To create a higher water potential in the fluid of the ascending limb.
• It also decreases the water potential of the medulla. -The water potential of the tissue fluid becomes much lower (much more negative) towards the bottom of the loop of Henle.

Question 7

What allows water to be moved out of the collecting duct and into the tissue fluid by osmosis?

Answer 7

• As fluid passes down the collecting duct, it passes through tissues with an ever decreasing water potential.
• Therefore there is always a water potential gradient between the fluid in the collecting duct and that in the tissues.
• This allows water to be moved out of the collecting duct and into the tissue fluid by osmosis.

Question 8

What is the arrangement of the loop of Henle described as?

Answer 8

A hairpin countercurrent multiplier system.

Question 9

What is the overall effect of the hairpin countercurrent multiplier system?

Answer 9

-To increase the efficiency of transfer of mineral ions from the ascending limb to the descending limb, in order to create the water potential gradient seen in the medulla.

Question 10

From the top of the ascending limb, the tubule fluid passes along a short distal convoluted tubule. What happens here?

Answer 10

-Active transport is used to adjust the concentrations of various mineral ions.

Question 11

From the distal convoluted tubule, where does the fluid go and describe its water potential?

Answer 11

• The fluid flows into the collecting duct At this stage the tubule fluid still contains a lot of water.
• it has a high water potrntial.

Question 12

Where does the collecting duct carry the fluid and what happens on the way?

Answer 12

• Back down through the medulla to the pelvis.
• As the tubule fluid passes down the collecting duct, water moves by osmosis from the tubule fluid into the surrounding tissue.
• It enters the blood capillaries by osmosis and is carried away.

Question 13

What does the amount of water reabsorbed depend on?

Answer 13

The permeability of the collecting duct walls.

Question 14

Describe the water potential and mineral content of urine once it reaches the pelvis?

Answer 14

• Very low water potential (very negative).

- And the concentration of minerals and urea is higher than in blood.

Question 15

Using the graph on page 35, describe:

1

Answer 15

Glucose decreases in concentration as it is selectively reabsorbed from the proximal tubule.

Question 16

Using the graph on page 35, describe:

2

Answer 16

• Sodium ions diffuse into the descending limb of the Henle causing the concentration to rise.
• They are then pumped out of the ascending limb, so the concentration falls.

Question 17

Using the graph on page 35, describe:

3

Answer 17

The urea concentration rises as water is withdrawn from the tubule. Urea is also actively moved into the tubule.

Question 18

Using the graph on page 35, describe:

4

Answer 18

• Sodium ions are removed from the tubule, but their concentration rises as water is removed from the tubule.
• Potassium ions increase in concentration as water is removed.
• Potassium ions are also actively transported into the tubule to be removed in urine.