Metabolism: Fasting State

Question 1

What percentage of catecholamine output is adrenaline?

Answer 1

80%

Question 2

Where is adrenaline synthesised?

Answer 2

Adrenal medulla

Question 3

How is adrenaline synthesised?

Answer 3

Water-soluble

Done in chromaffin cells of the medulla from AA tyrosine

Question 4

Secreted?

Answer 4

Granules released by exocytosis in response to “stressful” stimulus

Question 5

What does adrenaline do for glucose, circulation, heart and cellular energy use?

Answer 5

Increases glycogenolysis and lipolysis (fuels gluconeogenesis)
Constricts BVs to raise BP
Increases rate/contraction of heart and increases pulmonary ventilation
Increases energy use by ALL cells including O2 consumption

Question 6

What is a pheochromocytoma?

Answer 6

Adrenal tumour that secretes excess adrenaline, similar sympathetic symptoms to hyperthyroidism

Question 7

Postabsorptive state 6-12hrs

Answer 7

Glycogen mobilised from liver, brain and RBC take up most of the glucose (liver glycogen only lasts a few hours)
Muscle glycogen only for internal muscle use

Question 8

What does adrenaline do to the liver?

Answer 8

Activates cAMP signalling so glycogenolysis occurs and glucose is released
Decreased glycogen synthase
Increased glycogen phosphorylase
This is the opposite to insulin.

Question 9

Prolonged fasting response

Answer 9

• Once glycogen is depleted the liver changes to glucose production
• Glucagon released and stimulates gluconeogenesis from lactate, AAs and glycerol
• FFAs undergo beta-oxidation to give energy for the process
• In skeletal muscle lactate is made as a glycolytic product and recycled into glucose by the liver (Cori cycle) but only temporary use

Question 10

AAs in fasting

Answer 10

Released from muscle via proteolysis and glucogenic AAs degraded to pyruvate

• Intermediates converted to oxaloacetate (mainly alanine) for TCA
• Also only short term due to limited stores

Question 11

Fats in fasting

Answer 11

• FFAs mobilised but can’t be made into glucose, glycerol can and is released
• Adrenaline activates HSL to cause lipolysis

Question 12

Overall, what is needed for gluconeogenesis and how do we get it?

Answer 12

Energy: Beta-oxidation of FFAs

Lactate, glycerol and AAs from lipolysis and proteolysis

Question 13

Why are ketones made?

Answer 13

Prolonged starvation means no more glucose and lipolysis++ and lots of FFAs (can’t enter TCA) so excess acetyl-CoA is converted to ketones in the liver

Question 14

What hormones act using cAMP mechanisms?

Answer 14

Adrenaline, glucagon mainly

Other pituitary and endocrine hormones (ACTH, FSH, LH, PTH, TSH, calcitonin)