integration of metabolism

Question 1

outline metabolic features of the brain

Answer 1

requires continuous glucose supply
cannot use fatty acids
ketone bodies can partially substitute for glucose
hypoglycaemia causes faintness and coma
hyperglycaemia can cause irreversible damage
20% of resting metabolic rate

Question 2

outline metabolic features of the skeletal muscles

Answer 2

ATP requirements vary due to activity
light contraction- requirements met by oxidative phosphorylation
vigorous contraction- O2 becomes limiting
glycogen breakdown and lactate formation

Question 3

outline metabolic features of the heart

Answer 3

must beat constantly
designed for complete aerobic metabolism
the heart uses TCA cycle substrates
loss of O2 causes cell death(myocardial infarction)
10% of resting metabolic rate

Question 4

outline metabolic features of the liver

Answer 4

can interconvert nutrient types
glucose storage as glycogen
lipoprotein metabolism
20% of metabolic rate

Question 5

what can be used to make nucleotides

Answer 5

glucose-6-phosphate and backbones of TCA intermediates

this also generates the bulk of NADPH needed for anabolic pathways

Question 6

outline aerobic exercise in terms of muscles and liver

Answer 6

contractions increase ATP demand
contractions increase glucose transport
muscle glycolysis increases(adrenalin)
gluconeogenesis increases(adrenalin)
fatty acids increase(adrenalin)

Question 7

how is the increased glucose demand met for muscles in exercise?

Answer 7

increase in number of glucose transporters

Question 8

what to the requirements of muscle actomyosin ATPase balance with?

Answer 8

cations

Question 9

what is the role of adrenalin in exercise?

Answer 9

increases gluconeogenesis by liver

increases release of fatty acids from adipocytes

Question 10

outline anaerobic exercise in terms of muscles and liver

Answer 10

ATP demand cannot be matched by O2 delivery
transport cannot keep up with demand for glucose
muscle glycogen breakdown increases
lactate increases
liver uses lactate to form glucose(recovery)

Question 11

how and why are NAD+ levels replenished

Answer 11

to maintain glycolysis. pyruvate is taken up by liver and converted to lactate by lactate dehydrogenase(LDH)

Question 12

how are these pathways controlled

Answer 12

product inhibition

signalling molecules like hormones

Question 13

compare the isoforms of hexokinase in liver(Hk IV) and muscle(Hk I)

Answer 13

Hk I(muscle)
high glucose affinity (Km 0.1mM)
highly sensitive to G-6-P inhibition
Hk IV(liver)
low glucose affinity (Km 4mM)
less sensitive to G-6-P inhibition

Question 14

where is glucose 6-phosphatase present?

Answer 14

liver but not muscle (it catalyses the reverse of hexokinase)

Question 15

when is insulin secreted and what does it do?

Answer 15

when glucose levels rise

stimulates uptake and use of glucose and storage as glycogen and fat

Question 16

when is glucagon produced and what does it do?

Answer 16

when glucose levels fall

stimulates production of glucose by gluconeogenesis and breakdown of glycogen and fat

Question 17

what does adrenalin do ?

Answer 17

strong and fast metabolic effects to mobilise glucose for ‘fight or flight’

Question 18

what do glucocorticoids do?

Answer 18

steroid hormones that increase synthesis of metabolic enzymes concerned with glucose availability

Question 19

what is type I diabetes mellitus?

Answer 19

failure to secrete enough insulin(beta-cell dysfunction)

Question 20

what is type II diabetes mellitus?

Answer 20

failure to respond appropriately to insulin(insulin resistance)

Question 21

outline the complications of diabetes

Answer 21

hyperglycaemia with progressive tissue damage(retina, kidney, peripheral nerves etc)
increase in plasma fatty acids and lipoprotein levels with possible cardiovascular complications
increase in ketone bodies with the risk of acidosis
hypoglycaemia with consequent coma if insulin dosage is imperfectly controlled