Topic A7 Flashcards Preview

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Flashcards in Topic A7 Deck (6):

What conditions are required for each fate of glucose-6-phosphate in the liver?

1. Dephosphorylated by G6P to yield free glucose- occurs when [glucose] is low, glucagon is high and epinephrine is high
2. Made into liver glycogen by glycogen synthase- occurs when [glucose] is high, insulin is high
3. Enter glycolysis to make acetyl CoA to make fatty acids -> TAGs/phospholipids- occurs when [glucose] is high, insulin is high
4. Enter glycolysis to make acetyl CoA to make ATP via oxidative phosphorylation to provide ATP for the hepatocytes- only if [glucose] is high
5. Enter pentose phosphate pathway to yield NADPH and ribose-5-phosphate (for nucleotide synthesis)


What are ketone bodies?

- A source of energy that is made from acetyl-CoA in the liver
- Can enter the brain (unlike fatty acids which are bounds to serum albumin)
- oxidised for energy in place of/or to supplement glucose
- e.g. acetone, B-hydroxybutyrate, acetoacetate


What tissues is blood glucose essential?

- Brain (use ketones during starvation)
- Red Blood cells
- Bone marrow
- Renal medulla
- Peripheral nerves


Describe liver metabolism in the well fed state:

- Blood glucose is high- Insulin is present
- gluconeogenesis decreases
- glycolysis increases
- liver converts acetyl CoA made by glycoglysis into FAs -> TAGs and transports them to adipocytes for longterm storage
- glycogen synthesis increases


Describe liver metabolism is early starvation e.g. 12 hours after a meal:

- Blood glucose is low- glucagon is high
- gluconeogenesis increases (liver is making glucose for glucose dependent tissues)
- glycolysis decreases (glucose is not being broken down for energy/converted to FAs)
- glycogenolysis increases- produces glucose for other tissues
- fatty acids are being converted to acetyl CoA by B-oxidation for fuel for the liver and for production of ketones
- amino acids begin to be broken down from sources such as skeletal muscle protein
- adipocytes are cleaving TAGs


Describe what occurs during prolonged starvation e.g. days-weeks:

- fatty acids are the primary fuel source of the body
- contrary to early starvation there is a conservation of muscle protein
- reduction of glucose production
- increased B-oxidation: to produce acetyl-CoA for ketone body formation and for an energy source for cells
- excess of acetyl CoA compared to oxaloacetate (as oxaloactetate is being used for gluconeogenesis)