5.2.5- The function of the kidney 1

Question 1

In ultrafiltration what does the different in diameters allow the blood in the capillaries (of glomerulus) to do.

Answer 1

Ensures that the pressure is higher than that of the bowman’s capsule

Question 2

What is filtered out of the blood? (5 Points)

Answer 2

1) Water
2) Amino acids
3) glucose
4) urea
5) Inorganic mineral ions (NA, Cl, K)

Question 3

What is left in the capillary? (3 points)

Answer 3

1) Blood cells and proteins
2) Presence of the proteins means that the blood has a very negative water potential –> Ensures that some of the fluid is remained in the blood
3) The very low water potential of the blood in the capillaries is important to help reabsorb water

Question 4

What happens in the proximal convoluted tubule?

Answer 4

1) Fluid is altered by reabosorbtion of all the sugars, most mineral ions and some water (85%)
2) Cells of these tubules have a highly folded surface producing a brush border –> Increases surface area

Question 5

What happens in the descending limb of the loop of Henle?

Answer 5

1) Water potential is decreased by the addition of mineral ions and the removal of water

Question 6

What happens in the ascending limb of the loop of Henle?

Answer 6

Water potential is increased as mineral ions are removed by active transport

Question 7

What happens in the collecting duct?

Answer 7

The water potential is decreased again by the removal of water, the final product of the collecting duct is urine

Question 8

What happens to the urine from the collecting duct?

Answer 8

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

Question 9

What is selective reabsorption?

Answer 9

Involves active transport and cotransport where molecules are reabsorbed

Question 10

How are the cells lining the proximal convoluted specialised to achieve this reabsorption?

Answer 10

1) Cell surface membrane in contact with the tubule fluid is highly folded to form microvilli –> The microvilli increase the surface area for reabsorption
2) The cell surface membrane also contains special cotransporter proteins that transport glucose or amino acids in association with sodium ions, from the tubule into the cells
3) The opposite membrane of the cell, close to the tissue fluid and blood capillaries is also folded to increase its surface area. This membrane contains sodium/potassium pumps that pump sodium ions out of the cell and potassium ions into the cell
4) The cell cytoplasm has many mitochondria –> Indicates that an active or energy-requiring process is involved because many mitochondria will produce a lot of ATP.

Question 11

What is the mechanism behind reabsorption

Answer 11

1) Movement of ions and glucose into the cell is driven by the concentration gradient created by pumping sodium ions out of the cell.
2) Sodium ions move into the cell by facilitated diffusion but they cotransport glucose or amino acids against their concentration gradient. This is sometimes called secondary active transport
3) The movement of these substances reduces the water potential of the cells so that water is drawn in from the tubule by osmosis. As the substances move through to the blood, the water follows.