Fuel Metabolism

Question 1

Overview of the physiological processes which occur during the post-absorptive phase of metabolism.

Answer 1

Postabsorptive State= energy stores mobilised -> energy.

Fasting = glucose-> supply the brain

Glucagon Dominated (alpha cells, major site of activity is the liver): Increasing glycogenolysis, gluconeogenesis, ketogenesis.

Opposite to insulin.

Question 2

Describe the action of glucagon on Carbohydrates

Answer 2

• Decreases glycogen synthesis
• Promotes Gluconeogenesis
• Promotes Glycogenolysis

Question 3

Describe the action of glucagon on fats

Answer 3

• Promotes lipolysis and inhibits TG synthesis
• Production of Ketones

Question 4

Describe the action of glucagon on proteins

Answer 4

• Inhibits hepatic protein synthsis
• Promotes degradation of hepatic protein. (no effect on muscle protein)

Question 5

What are the main stimuli to promote glucagon secretion?

Answer 5

• Decreased [plasma glu] = activates alpha cell and deactivates beta cells.
• Decreased FFA = Increased Glucagon
• Increased blood [amino acids]

Question 6

Describe the action of glucagon and glucocorticoids at the cellular level : Liver

Answer 6

Lipid and amino acid breakdown (glucocorticoids)= Ketone Bodies -> All tissues (ATP Production)

Gluconeogenesis (glucocorticoids) and Glycogenolysis (glucagon + epinephrine) = Glucose -> Neural Tissue (ATP Production)

Question 7

Describe the action of glucagon and glucocorticoids at the cellular level: Adipose Tissue

Answer 7

TG breakdown (epinephrine + glucocorticoids) = Lipids -> All tissues except neural (ATP production)

Question 8

Describe the action of glucagon and glucocorticoids at the cellular level: Skeletal Muscle

Answer 8

Protein breakdown by cathepsins (glucocorticoids) = Amino Acids -> Liver ( Gluconeogenesis + Ketone body production)

Glycogen breakdown (glucagon + epinephrine) = Lactic Acid -> Liver (Glluconeogenesis)

Question 9

Why does an increase in blood amino acid concentration increase glucagon secretion?

Answer 9

A rise in blood amino acid concentration (the result of protein metabolism) stimulates the secretion of both glucagon and insulin, so their blood sugar remains stable.

The insulin is secreted to stimulate protein synthesis–the uptake of amino acids into muscle cells–making them less available for gluconeogenesis. The glucagon is secreted to stimulate the uptake of amino acids into the cells of the liver for gluconeogenesis.