Lecture 36: STARVATION Flashcards
What is needed for survival during starvation?
supply the brain with fuels, supply other tissues with fuels and conserve as much protein as possible
How much fuel does the brain use?
120g of glucose per day
What is the fuel for other tissues?
Mainly fatty acids
Why does protein need to be conserved?
To maintain structure and function
What is the main hormone involved in survival during starvation?
GLucagon
Where is glucagon produced?
By pancreas alpha cells when blood glucose drops
How much fat is there?
At leas 15kg
How much energy does the fat stores give?
Enough for at least 40 days of starvation
What stimulates lipolysis?
Glucagon
What can fatty acids be used by?
All aerobic tissues except the brain
What are TAG’s broken down into?
glycerol and free fatty acids (complexed to albumin in blood)
What breaks down triacylyglycerols?
Hormone sensitive lipase
What stimulates hormone sensitive lipase?
Glucagon and adrenaline
What does glycerol do?
Enters the blood and goes to the liver
What do free fatty acids do?
Go to all aerobic tissues except the brain
How much glucose comes from glycerol?
Around 20g
How much glucose is in liver glycogen?
About 90-120g (enough for 1 day)
What happens to liver glycogen?
It is mobilised back to glucose
What is glycogenolysis stimulated by?
Glucagon
What enzymes are used in glycogenolysis?
Glycogen phosphorylase and debranching enzyme
What is the first step of glycogenolysis?
Glycogen + Pi > glucose-1-phosphate catalysed by phosphorylase
What is the second step of glycolysis?
Glucose-1-phosphate <> glucose-6-phosphate catalysed by mutase
What is the third step of glycgenolysis?
Glucose-6-phosphate + H2O > glucose + Pi catalysed by glucose-6-phosphatase
Where does gluconeogenesis occur?
Mainly in the liver (also kidney cortex)
What is gluconeogenesis?
The synthesis of glucose from lactate, alanine and glycerol (3 carbon compounds)
where is lactate from?
Muscle glycogen
Where is alanine from?
Muscle protein
Where is glycerol from?
Adipose tissue (TAG)
What is gluconeogenesis stimulated by?
Glucagon
What provides the energy (ATP) required fro gluconeogenesis?
Fatty acid oxidaiton
What uses most of the glucose from gluconeogenesis?
The brain
Can fatty acids (acetyl CoA) be used to make glucose?
No, because they are 2C compounds but can via beta oxidation provide ATP and NADH for gluconeogenesis
How much protein is in the body?
10-15kg
Is there specific storage proteins?
No
What must happen with some protein?
It must be degraded to amino acids to make glucose
What can loss of too much protein cause?
Structural and functional damage so proteins must be conserved as much as possible
How are ketone bodies synthesised?
In the liver from fatty acids
What is the process of forming ketone bodies?
mobilisation of TAG’s from adipose tissue > fatty acids > 2acetyl-CoA via beta oxidation > acetoacetate via ketogenesis <> beta hydroxybutyrate
What are the ketone bodies?
Acetoacetate and beta hydroxybutyrate
What are ketone bodies used by?
The starving brain as an energy source
How much energy comes from ketone bodies?
50g/day (still need 50g of alanine)
What can fatty acids be used by?
Essentially all aerobic tissues (except brain); essentially unlimited supply from TAG’s
What are used by the brain?
Ketone bodies
What happens as a result of the brain using ketone bodies?
It needs less glucose (only about 50g/day) so muscle degradation can slow down (not so many amino acids needed for gluconeogenesis) and the body can survive for longer
