The Liver and Gluconeogenesis Flashcards
What is the physiological circulating blood glucose concentration?
3.9-6.2mM
What is the average fasting blood glucose concentration?
4.4-5.0 mM
What happens if your blood glucose levels drop below 2.5mM?
Coma and death
What happens if your blood glucose levels rise above 6.2mM?
Dehydration, wastage of body tissue > death
Give 3 advantages of glucose as a metabolic fuel.
- Water soluble - does not require a carrier molecule in circulation.
- Can cross the blood-brain barrier
- Can be oxidised anaerobically - e.g. in erythrocytes.
Give 3 disadvantages of glucose as a metabolic fuel.
- Relatively low yield of ATP/mole compared to fatty acids.
- Osmotically active so cannot be stored easily.
- High concentrations can directly damage cells or lead to accumulation of toxic products.
What is gluconeogensis?
Process of glucose generation from non-glucose sources.
Give 3 sources of blood glucose.
- Dietary glucose
- Liver glycogen - glycogenolysis
- Gluconeogensis - from fat and glucogenic amino acids
When does gluconeogensis occur?
During carbohydrate deprivation
Give the 3 irreversible reactions in glycolysis.
Hexokinase/glucokinase (converts glucose to glucose-6-phosphate)
Phosphofructokinase (converts fructose-6-phosphate to fructose-1,6-bisphosphate)
Pyruvate kinase (converts phosphoenol pyruvate to pyruvate)
How are the 3 irreversible reactions over come in gluconeogensis to regenerate glucose?
Pyruvate carboxylase and PEP carboxkinase convert pyruvate to phosphoenolpyruvate.
Fructose-1,6-bisphosphatase converts fructose-1,6-bisphosphate back to fructose-6-phosphate.
Glucose-6-phosphatase converts glucose-6-phosphate back to glucose.
How is gluconeogensis regulated?
Mobilisation of substrate.
Activation of enzymes by glucagon. (pyruvate carboxylase is activated by acetyl CoA)
What happens in gluconeogensis at the muscle?
Alanine and lactate are released in anaerobic respiration and converted to pyruvate.
Name the main two hormones which regulate blood glucose and control gluconeogensis.
Insulin (produced by beta-cells in the Islets of Langerhans)
Glucagon (produced by alpha-cells in the Islets of Langerhans)
What is insulin?
An anabolic hormone - promotes synthesis and storage
Secreted by beta-cells in the Islets of Langerhans in the pancreas.
What is the function of insulin?
To decrease blood glucose concentration.
How does insulin lower blood glucose levels?
Inhibits gluconeogensis.
Activates glycogen synthesis in muscle and liver.
Activates fatty acid synthesis.
What is the difference between GLUT1,2,3,4 transporters? Where are they found?
GLUT1 found on erythrocytes.
GLUT2 found on liver cells.
GLUT3 mainly found on brain cells.
GLUT4 found on muscle cells.
GLUT1 and GLUT3 have higher affinity for glucose - hence brain and erythrocyte are priority organs as they can only use glucose as a source of fuel.
GLUT2 has a lower affinity and is NON-insulin dependent.
GLUT4 has a lower affinity and is insulin-dependent (glucose will only enter muscle cells when insulin is present)
What is glucagon?
Catabolic hormone
Promotes degradation of stored fuel
What is the function of glucagon?
To increase blood glucose levels.
How does glucagon increase blood glucose levels?
Increases glycogenolysis and gluconeogensis.
Increases circulating fatty acids and ketone bodies.
Increases apidose tissue lipolysis and fatty acid oxidation.
