starvation

Question 1

What are the main ideas of metabolic homeostasis during starvation

Answer 1

Spare the use of glucose by tissues to conserve it for the brain, other tissues can use alternative fuel sources from adipose stores. maintains the blood glucose levels

brain requires around 120g glucoser per day - gluconeogenesis helps supply this

Question 2

How does fuel utilization of glucose, adipose and proteins change between fasting and starvation states

Answer 2

Glucose - glycogen stores run out and gluconeogenesis in liver and kidney takes over to maintain blood glucose levels. Spares glucose use in other tissues reserved for brain

TAG breakdown increases in adipose - glycerol used in gluconeogenesis - FFA used to make ketones
- beta-hydroxybutyrate + acetoacetate

Protein breakdown initally then spared due to requirements for function and structure
- indicated by lower unirary amonium and urea

Question 3

What hormones are reponsable for the starvation reponse

Answer 3

Glucagon - promotes FFA mobilisation + gluconeogenesis
- inhibits phosphorylation of FoxO1 transcription factor for gluconeogenesis -> increased transcription of enzymes required for branch points of reverse glycolysis

Cortisol + adernline also play a role

Question 4

What is a branch point

Answer 4

Most metabolic processes can go forwards and backwards with the same enzymes. Branch points are locations where a different enzyme is required for forward and backwards reactions
- points are highly regulated
FoxO1 regulates for glycolysis

Question 5

How are fuels interchanged between tissues during starvation

Answer 5

Fatty acids move from adipose to liver -
- increased rate of beta oxidation -> increased acetyl-CoA -> ketongenisis -> increased ketone bodys
Fatty acids move to muscle for fuel

Ketone bodys - used by the brain to reduce its requirements for glucose
- ketone body broken back to acetyl-CoA -> used in metabolic processes

Question 6

What are gluconeogenic precursours and how do they become glucose

Answer 6

Lactate - from RBC or anerobic muscles -> can be used to make pyruvate then reversed glycolysis

alanine - from proteolysis moves to liver in blood -> turned to pyruvate -> reversed glycolysis

glycerol from FFA breakdown moves to liver -> enteres reverse glycolysis halfway through G3P

Question 7

How does the metabolium of alcohol imapct gluconeogenesis

Answer 7

Alcohol -> acetalalderhyde -> acetate