Lecture 35: Starvation

Question 1

What are the main energy sources used by a starving person?

Answer 1

• Triacyglycerol stores - enough energy for 40 days
• Liver glycogen - provides enough glucose for the brain for one day
• Protein stores - must be conserved as much as possible

Question 2

Outline the pathway of glycogen mobilisation in the liver:

• what are the enzymes involved?

Answer 2

• liver glycogen is mobilised back into glucose
• stimulated by the hormone , glucagon
• provides enough glucose form the brain for one day
  enzymes involved = glycogen phosphorylase + de-branching enzyme

Question 3

Name and give the structures and sources of the main precursors used by the liver for gluconeogenesis

Answer 3

Gluconeogenesis
=occurs mainly in liver (also kidney)
= synthesis of glucose from
- lactate from muscle glycogen
- alanine from muscle protein
- glycerol from adipose tissue (TAG)
=stimulated by glucagon
=fatty acid oxidation provides the energy required
=brain uses most of the glucose

Question 4

Why is ketone body synthesis important for a starving person?

Answer 4

Ketone bodies are used as fuel source by the brain

• fatty acids are too large to cross the blood brian barrier
• ketone bodies are synthesised in the liver from fatty acids

Question 5

What are the metabolic adaptations that allow people to survive without food for 40 days before dieing?

Answer 5

• fatty acids can be used as a fuel by all aerobic tissues (except brain); essentially unlimited supply from TAGs
• ketone bodies used by brain
  ——> therefore brain needs less glucose; now only about 50g/day muscle degradation can slow down
  ——> body can survive for longer

Question 6

How are triacglycerol stores mobilised in adipose tissue?

Answer 6

• at least 15 kg of fat
• enough energy for at least 40 days of starvation
• glucagon stimulates lipolysis
• fatty acids used as fuel by all aerobic tissues, EXCEPT BRAIN

Question 7

Describe the importance of protein stores?

Answer 7

• 10-15kg protein in body
• BUT no specific storage proteins
• some protein must be degraded to amino acids to make glucose
• loss of too much protein causes structural and functional
• protein must be conserved as much as possible