Excretion

Question 1

What is excretion?

Answer 1

Removal of metabolic waste from the body that is by products or unwanted substances from normal cell processes

Question 2

The liver

Answer 2

All cells carry out same function
Regenerates itself
Body can’t store amino acids or proteins so it is processed by liver where toxic groups are removed and useful energy is preserved

Question 3

Processing of amino acids in the liver: deamination

Answer 3

Toxic amino group removed

Amino acid+ oxygen — Keto acid + ammonia

Question 4

Processing of amino acids in the liver: formation or urea

Answer 4

Ornithine cycle

Ammonia + carbon dioxide — urea + water

Question 5

Urea compared to ammonia

Answer 5

Urea is less soluble and less toxic than ammonia so it can be safely transported in blood to kidneys

Question 6

What is the function of a nephron

Answer 6

Remove excess of water waste and other substances from the blood
Regulate water levels
Regulate electrolyte levels

Question 7

What is ultrafiltration?

Answer 7

Fluid from the blood is pushed into the bowmans capsule

Question 8

Why does the afferent arteriole have a larger lumen than the efferent arteriole

Answer 8

Creates high pressure forcing liquid out

Question 9

Stages of excretion

Answer 9

Ultrafiltration

Tubular reabsorption

Countercurrent multiplication

Distal convoluted tubule

Collecting duct (osmoregulation)

Question 10

Ultrafiltration: what 3 layers does the barrier between the blood in the capillary and the linen of the bowmans capsule consist of?

Answer 10

Endothelium of capillary

Basement membrane

Epithelial cells of bowmans capsule (podocytes)

Question 11

What does the glomerular filtrate contain?

Answer 11

Water 
Amino acids 
Glucose 
Urea 
Inorganic ions 
Waste products

Question 12

Where does tubular reabsorption take place

Answer 12

The proximal convoluted tubule

Question 13

Process of tubular reabsorption

Answer 13

Active transport move sodium ions from surrounding cells to the blood
Co transport of glucose and amino acid’s with sodium as the concentration gradient has been established
All glucose and amino acid’s are reabsorbed
Water potential in plasma is lower than filtrate so water moves by osmosis from nephron into blood

Question 14

Where does counter current multiplication take place

Answer 14

Loop of Henle

Question 15

Process of counter current multiplication

Answer 15

Salts are actively pumped out of wider part of ascending limb into surrounding tissue

Water potential is reduced in tissues

Water leaves descending limb by osmosis into tissues

Filtrate in the thin part of ascending limb is more concentrated so salts diffuse out passively

Question 16

Results of counter current multiplication

Answer 16

Consistently higher salt concentration in tissues so more water is reabsorbed

Question 17

The kangaroo rat

Answer 17

Has a longer Medulla and a long loop of Henle so more water can be reabsorbed as it’s a steep concentration gradient

Question 18

What happens at the distal convoluted tubule?

Answer 18

Active reabsorption of sodium ions followed by osmotic movement of water

Question 19

What happens at the distal convoluted tubule when the salt conc is low in the body?

Answer 19

Aldosterone stimulates reabsorption of sodium by making it permeable to salts

Question 20

Osmoregulation in the collecting duct

Answer 20

Walls not permeable to water

High salt conc in tissues so water reabsorbed making urine more concentrated

Question 21

What happens in the collecting duct if dehydrated?

Answer 21

ADH released to make duct permeable to water