Insulin - Counter regulatory hormone Flashcards
What is the key role of insulin in controlling blood glucose levels
1, high glucose levels – removal of glucose from the blood (transport)
- Synthesis of glycogen and triglycerides to store energy
- Inhibition of processes that release glucose/fatty acids
What is the main hormone that is used in fasting to control blood glucose levels
Glucaogn
describe what metabolism is like during fasting
- Low glucose levels –No glucose transport
- Glycogen and triglycerides are not synthesised anymore
- Processes that release glucose/fatty acids are not inhibited anymore
describe the structure of glucagon
- 29 amino acids
- one chain only
what islets of langhernas produce glucagon
alpha
describe how synthesis of glucagon takes place
- Frist synthesised as a preproglucagon
- Broken down into a proglucagon
- This is then broken down into a glucagon
name another hormone that comes from the same precursor as glucagon
GLP-1
how low is blood glucose in order to do glucagon secretion
- Stimulated by low blood glucose concentration – normal fasting levels of glucose is 80-90mg/100ml
what causes an increase in glucagon secretion
- Exercise - In exhaustive exercise blood concentration of glucagon increases four to five fold
(increased circulating amino acids or β-adrenergic stimulation may play a role)
what inhibits glucagon secretion
- inulin - it breaks down cAMP by phosphodiesterase enzyme
- somatostatin (produced by delta cells in the islet of langerhans)
what are the effects of glucagon
Increases glycogenolysis in the liver.
Increased uptake of amino acids in the liver.
Increases gluconeogenesis in the liver (amino acids, glycerol and lactate).
Liver glycolysis is inhibited by inhibiting pyruvate kinase and PFK1.
Increased lipolysis, glucagon activates hormone sensitive lipase (HSL).
More ketogenesis is able to occur.
how is glucagon receptor signalled
- The glucagon receptor is a G protein coupled receptor
- GPCRs contain 7 transmembrane domains are coupled to trimeric G proteins
- Dissociation of the trimer upon ligand binding to the receptor activates the signalling cascade
- In the absence of glucose, it is assembled in the trimeric form and the 3 subunits are joined together
- This activates adenylase cyclase and this activates cAMP
- The cAMP which is produced in this reaction triggers the cascade
- cAMP is produced and this activates PKA and then this increases phosphorylase kinase and activates the rest of the cascade causing glycogenolysis
what is CPT1
Important enzyme in the Beta oxidation of fatty acids into Acetyl-CoA.
what inhibits CPT1 and what activates CPT1
CPT1 is inhibited by insulin.
It is activated by glucagon.
what happens in prolonged glucagon
Oxaloacetate replaces amino acids as the main source for gluconeogenesis.
Acetyl-CoA is converted into acetoacetate (ketone) via HMG-CoA.
Glucagon inhibits HMG-CoA to prevent excess cholesterol and TGA formation.
But, glucagon increases ketogenesis.
what does triglycerides break down into
glycerol and free fatty acids
- glycerol is used in gluconeogensis
what does amlonyl CoA inhibit
- Malonyl-CoA inhibits transport of FFAs into mitochondria via CPT-1 therefore inhibiting β oxidation
what is oxaloacate used int he liver by
- oxaloacetate is used by the liver as substrate for gluconeogensis