The liver and glucose metabolism Flashcards
Features that make a good fuel
- Must be able to be stored when in excess.
- Must be able to be released during processes that require high amounts of ATP.
Brain metabolism
The brain can only metabolise glucose or ketone bodies.
The brain cannot store large amount of glucose nor can it synthesise glucose.
The brain is unable to extract glucose if it has low concentrations in the blood due to the lack of sensitivity to hormones.
Hence neuronal cells have to constantly draw glucose from the blood- blood glucose concentration must be maintained.
Plasma glucose concentration limits
2.5-8.8mM
Processes that increase blood glucose levels.
- Hormones that influence this
Gluconeogenesis
Glycogenolysis
Diet
Hormones:
- Cortisol
- Glucagon
- Catecholamines (adrenaline, noradrenaline)
- Growth hormone
Processes that decrease blood glucose levels.
- Hormones that influence this
Glycogenesis
Fatty acid synthesis
Hormones:
Insulin
Phases of assimilation after a meal
- Asorptive events:
immediate events- liver and adipose tissue taken up materials. - Post-absorptive:
between meals- liver and adipose export materials
Insulin and entry of glucose into cells
Insulin can influence the entry of cells only via the Glut4 (glucose transporter).
Insulin binds to insulin receptor and activates PI-3 kinase.
This stimulates the activation and translocation of the Glut4 glucose transporter- expressed on the plasma membrane.
This allows the entry of more glucose into the cell.
Glut 1
Glucose transporter that is the most widely expressed on cells.
Has a very high affinity for glucose- 1mM.
Glut 2
Glucose transporter found:
- Liver
- Pancreatic beta cells
- Small intestines
Has very low affinity for glucose: 15-20mM.
This transporter does not take up glucose unless if concentrations are very high
- Allows glucose to be distributed everywhere
Glut 3
Glucose transporter found in:
- Brain
Has a very high affinity for glucose- 1mM. Draws glucose from blood even at low concentrations.
Glut 4
Glucose transporter found in:
- Muscle
- Adipose tissue
This is the only Glut sensitive to insulin.
Affinity for glucose at 5mM
Immediate cellular effects of insulin
These effects occurs at insulin concentrations 10-9 to 10-8.
Effects:
- Increase glucose uptake in muscle and adipose tissue.
- Modulates enzyme activity in glucose metabolism (in liver)
Cellular effects of insulin after prolonged exposure
This occurs over several hours after continuous exposure of insulin at concentration around 10-8.
Effects:
- Increases enzymes that make glycogen in the liver.
- Increase enzymes that make TGs in adipocytes
- Inhibits lipolysis
Pentose phosphate pathway
A branch of glycolysis at G-6-P.
This pathway produces:
- Ribose phosphate for DNA and RNA
- NADPH
Liver and adipose tissue have a lot of enzymes for this pathway
Glucose metabolism in the RBCs
Glut 1—>Glucose —> G6P—-> Lactate
- G6P can branch into the pentose phosphate pathway.
RBCs cannot aerobically respire due to lack of mitochondria.
