5.2.5 functon of kidney 1

Question 1

ultrafiltration

Answer 1

filtering of blood at molecular level

Question 2

why is blood in capillaries of glomerulus higher pressure than bowman’s capsule

Answer 2

• blood flows into glomerulus via afferent arteriole
• wider than efferent arteriole (carries blood away from glomerulus)

Question 3

what’s filtered out of blood into bowman’s capsule

Answer 3

–> blood plasma:
- water
- amino acids
- glucose
- urea
- inorganic mineral ions eg. sodium, chloride, potassium

Question 4

what’s left in capillaries of glomerulus

Answer 4

blood cells & proteins

Question 5

what does presence of protein in blood in glomerulus cause

Answer 5

very low (negative) water potential = some of fluid retained in blood

Question 6

selective reabsorption

Answer 6

substances absorbed back into tissue fluid & blood capillaries surrounding nephron

Question 7

selective reabsorption in proximal convoluted tubule

Answer 7

• fluid altered by reabsorption of all sugars, most mineral ions & some water
• ~85% of fluid reabsorbed

Question 8

how do cells in PCT help reabsorption

Answer 8

highly folded surface = brush border
–> increases SA

Question 9

selective reabsorption in descending limb of loop of Henle

Answer 9

water potential of fluid decreased by addition of mineral ions & removal of water

Question 10

selective reabsorption in ascending limb of loop of Henle

Answer 10

water potential increased as mineral ions removed by active transport

Question 11

selective reabsorption in collecting duct

Answer 11

water potential decreased again by removal of water
–> final product = urine

Question 12

what does reabsorption involve

Answer 12

active transport & cotransporters

Question 13

how are the cells lining the PCT specialised to achieve reabsorption

Answer 13

1. (apical side) cell surface membrane in contact with tubule fluid is highly folded forming microvilli = increase SA
2. cell surface membrane contains cotransporter proteins which transport glucose/amino acids (in association with sodium ions) from tubule –> cell
3. (basal side) opposite membrane of cell (close to tissue fluid/blood capillaries) folded = increases SA
   - membrane consists of sodium/potassium pumps which pump sodium ions out of cells & potassium ions into cell
4. cell cytoplasm has many mitochondria = produce lots of ATP

Question 14

describe the steps involved in selective reabsorption in the PCT

Answer 14

1. sodium ions actively pumped out of cells lining tubule (basal side)
2. concentration of sodium ions in cytoplasm of cell decreases = creates concentration gradient
3. sodium ions diffuse into cell through cotransporter protein - carries glucose or amino acid with it (facilitated diffusion) = SECONDARY ACTIVE TRANSPORT
4. water moves into cell by osmosis (as water potential lower in cell)
5. glucose/amino acids diffuse into blood capillaries

Question 15

how can larger molecules which may have entered the tubule be absorbed

Answer 15

endocytosis