5.2.5: The function of the kidney 1

Question 1

What is ultrafiltration?

Answer 1

Ultrafiltration s the filtering of blood at the molecular level.

Question 2

Which arterioles transport blood into and out of the glomerulus?
Which is wider?

Answer 2

Blood flows into the glomerulus through the afferent arteriole, which is wider than the efferent arteriole that carries the blood away from glomerulus.

Question 3

what does the difference in diameters ensure?

Answer 3

• ensures that the blood in the capillaries of the glomerulus maintains a pressure higher than in the Bowman’s capsule.
• This pressure difference tends to push fluid from the blood into the Bowman’s capsule that surrounds the glomerulus.

Question 4

Overall, where does the blood plasma containing dissolved substances get pushed to in ultrafiltration?

Answer 4

Blood plasma containing dissolved substances is pushed under pressure from the capillary into the lumen of the Bowman’s capsule.

Question 5

What does the blood plasma contain?

Answer 5

• water
• amino acids
• glucose
• urea
• inorganic mineral ions (sodium, chloride, potassium)

Question 6

why are the concentrations of dissolved solutes variable?

Answer 6

-the concentration of dissolved solutes will depend on the water balance in the organism and are therefore variable.

Question 7

What ensures that some of the fluid is retained in the blood after ultrafiltration?
What is contained in this fluid?

Answer 7

• Blood cells and proteins are left in the capillaries.
• The presence of proteins means the blood has a very low water potential.
• This ensures that some of the fluid is retained in the blood, and this contains some of the water and dissolved substances found in blood plasma.

Question 8

Why is it important that the blood in the capillaries have a low water potential?

Answer 8

-The very low water potential of the blood in the capillaries is important to help reabsorb at a later stage.

Question 9

As the fluid from the Bowman’s capsule passes along the nephron tubule, how is its composition is altered?

Answer 9

• By selective reabsorption

- substances are absorbed back into the tissue fluid and blood capillaries surrounding the nephron.

Question 10

What happens in the proximal convoluted tubule?

Answer 10

• The fluid is altered by the reabsorption of all the sugars, most mineral ions and some water.
• In total 85% of the fluid is reabsorbed here.

Question 11

What increases the surface area in the proximal convoluted tubule?

Answer 11

-The cells of the tubules have a highly folded surface producing a brush border which increases surface area.

Question 12

How is the water potential of the fluid decreased in the descending limb of the loop of Henle?

Answer 12

-By the addition of minerals and the removal of water.

Question 13

How is the water potential increased in the ascending limb of the loop of Henle?

Answer 13

Mineral ions are removed by active transport.

Question 14

How is water potential decreased again in the collecting ducts?`

Answer 14

By the removal of water

Question 15

What is the final product in the collecting duct?

Answer 15

Urine

Question 16

Why does the final product (urine) need to have a low water potential?

Answer 16

-The urine needs to have a higher concentration of solutes than found in the blood and tissue fluid.

Question 17

Where does the urine go after ultrafiltration?

Answer 17

Urine passes into the pelvis and down the ureter to the bladder.

Question 18

Which two processes does reabsorption involve?

Answer 18

• Active transport

- Cotransport

Question 19

Describe the cell surface membrane in contact with the tubule fluid and how it is well adapted for reabsorption.

Answer 19

• The cell surface membrane in contact with the tubule fluid is highly folded to form microvilli.
• The microvilli increase the surface area for reabsorption.

Question 20

-The cell surface membranes contain special cotransporter proteins. What do these do?

Answer 20

-They transport glucose or amino acids, in association with sodium ions, from the tubule into the cell.

Question 21

The opposite membrane of the cell (close to the tissue fluid and blood capillaries), is also folded to increase its surface area. What types of proteins does this membrane contain?

Answer 21

-Sodium/potassium pumps that pump sodium ions out of the cell and potassium ions into the cells.

Question 22

The cell cytoplasm has many mitochondria. What does this indicate?

Answer 22

• That an active, or energy-requiring process is involved

- because many mitochondria will produce a lot of ATP.

Question 23

In selective reabsorption, what drives the movement of sodium ions and glucose into the cell?

Answer 23

The concentration gradient created by pumping sodium ions out of the cell.

Question 24

Describe why the movement of sodium ions into the cell is described as secondary active transport.

Answer 24

• Sodium ions move into the cell by facilitated diffusion…
• but they cotransport glucose or amino acids against their concentration gradient.

Question 25

Why is water drawn into the tubule by osmosis?

Answer 25

• The movement of glucose and amino acids into the cells reduces their water potential.
• Water is drawn in from the tubule by osmosis.
• As the substances move through the blood, water flows.

Question 26

How can larger molecules, such as small proteins that have entered the tubule be reabsorbed?

Answer 26

By endocytosis.