Carbohydrate metabolism and blood glucose control Flashcards
(46 cards)
Explain Carbohydrate Metabolism
1- Dietary sugar and starch ingested are transformed to fructose, galactose and glucose
2- metabolized in liver
3- then used via glycolysis & TCA cycle to generate energy
what happens in the case of no glucose in body from food
Glucose can be synthesized through fat or amino acids , if there is no glucose available to use
How does the liver convert fructose and galactose to glucose ?
Why must it be converted ?
- the enzyme glucose 6-phosphatase , which hepatocytes contain in large amounts converts them to glucose
- glucose is the final pathway for carbs to be transported into tissue cells
How does glucose transport through the cell membrane
- Glucose is transported by facilitated diffusion across the cell membrane
- this involves protein transporters binding with glucose to move it across the membrane
What are GLUT proteins, what is the difference between the types and what is their function
- glucose transporters that mediate the concentration of glucose uptake in tissues
- some are more efficient than others, those are often found in tissue that requires a lot of energy ( ex: brain , RBC, cornea, CNS ) GLUT 1&3 > GLUT 2&4
How is glucose absorption in GI different
requires active sodium-glucose co-transport
What is the main regulator of glucose concentration
Insulin
Describe Insulin, why it is secreted and it’s degradation
- large polypeptide hormone of 2 amino acid chains
- produced by pancreatic B-cells in islets of langerhans
- secretion is stimulated by increase of blood glucose levels
- degraded in liver after 6 min
How is insulin secreted
- high levels of ATP close potassium channels in Beta cell
- membrane depolarization opens Calcium channels
- calcium is insulin secretion signal
- preformed insulin is produced by ER , gets processed through Golgi and then insulin is released into blood stream
What are Sulfonylureas
drugs used to treat type 2 diabetes , close potassium channels to increase insulin secretion
what is Glucagon-like peptide
drug that increases insulin secretion by opening calcium channels
What is the effect of Somatostatin and Norepinephrine on Insulin
reduce insulin secretion
When are insulin levels highest , how long does it last
after a meal , 2-3 hours
Graph relationship with insulin secretion and glucose
linear relation
Minor factors regulating insulin secretion
- levels of circulating amino acids in blood: can stimulate insulin which increases protein tissue uptake
- GI hormones : while eating
- Autonomic nervous system: stress decreases secretion , eating / relaxing increases secretion
Effect of insulin on adipose tissue
increase glucose uptake = lipogenesis ( store fat) decrease lipolysis ( breakdown of fat )
Effect of High insulin on liver
Increase glucokinase and thus glucose uptake
increase glycogen synthesis , storing glycogen
decrease gluconeogenesis ( break down of glucose)
Effect of insulin on striated muscle
increase glucose uptake, glycogen synthesis, protein synthesis
Effect of Insulin on glucose facilitated diffusion
- in fasting conditions : muscle GLUT4 does not take up glucose at low levels, will use fat instead
- GLUT4 in insulin presence will increase glucose uptake , increasing facilitated diffusion
Exercise effect on Glucose facilitated diffusion
muscles active = glucose diffused to be used for energy
muscles inactive = glucose turned to glycogen
Effect of low insulin on liver
- increase glycogen phosphorylase which increases glycogen breakdown
- increase glucose 6 phosphatase which increase glucose release from liver
Effect of insulin on Brain
- Insulin has minimal effect on brain glucose uptake
- GLUT 1 is always readily taking up glucose
What happens due to hypoglycaemia ( symptoms )
nervous irritability, fainting, convulsions , coma
What is the major site of glucose uptake
muscle
