insulin production, secretion and action Flashcards
(42 cards)
Which organ produces insulin?
The pancreas produces insulin.
What are the cells of the endocrine pancreas called?
The cells of the endocrine pancreas are called Islet of Langerhan cells
What hormone do beta cells produce?
Beta cells produce insulin.
What hormone do alpha cells produce?
Alpha cells produce glucagon.
What hormone do delta cells produce?
Delta cells produce somatostatin.
What hormone do gamma cells produce?
Gamma cells produce pancreatic polypeptide
In which specific part of beta cells is insulin synthesised?
Insulin is specifically synthesised in the rough endoplasmic reticulum of pancreatic beta cells.
What is insulin cleaved from?
Insulin is cleaved from a precursor called preroninsulin/
What is Connecting Peptide?
Connecting Peptide i.e. C Peptide is a by- product of the cleavage of preproinsulin which has no physiological function
What is measuring C-Peptide useful for?
By measuring the assay levels of C-Peptide you can determine the levels of insulin being produced by the pancreas.
What is the process involved in the secretion of insulin?
- Glucose enters the beta cells of the pancreas through the GLUT 2 transporter before being phosphorylated by GLUCOKINASE to become glucose-6-phosphate.
- The glucose-6-phosphate then undergoes glycolysis which results in the production of acetyl-coA which in turn enters the citric acid cycle and produces 36 ATP
- The ATP produced then binds to the Potassium ATP channel which results in its blockage causing depolarisation of the beta cell membrane.
- The depolarisation which occurs activates the voltage activated calcium channels which allows calcium to enter the cell membrane
- The calcium then binds to calcium receptors on insulin vesicles resulting in the exocytosis of insulin.
What is important about the Km of glucokinase?
The Km of glucokinase lies within physiological concentrations of glucose levels, this ensures that at very low concentrations of glucose; glucokinase does not convert glucose to glucose-6-phospahte.
1 molecular of glucose produces how many ATP?
36 ATP
At which point should insulin be realised?
Insulin should only be released during times when blood glucose levels are rising above 5mM
The release of insulin is termed?
- The release of insulin is termed bi-phasic.
- This means that 5% of insulin granules are always available for immediate release during the rapid 1st phase of insulin secretion.
- The second phase of insulin secretion depends on the resultant blood glucose levels after the first phase of release
type 1 diabetets
type 4 hypersensitivity reaction which destroys beta cells in the islet of langerhans which results in the production of no insulin
type 2 diabetes
initially there is hyperinsulinaemia in response to the hyperglycaemia but the insulin receptors in tissue have reduced sensitivity to the insulin (known as insulin resistance) eventually the beta cells may become unable to produce enough insulin to keep up with the hyperglycaemia
drugs used in diabetes
sulfonylurea drugs which mimic the action of ATP by blocking the ATP dependant potassium channel resulting in the depolarisation of the cell membrane and the release of insulin
when are sulfonylurea drugs used
2nd line for type 2 diabetes and for MODY
examples of sulfonylurea drugs
tolbutamide and glibenclamide
structure of potassium ATP channels
consists of 2 proteins: Kir6 and SUR1
drugs which have the opposite affect of sulfonylurea drugs
diazoxide which stimulates the potassium ATP channels which inhibits the depolarisation of the cell membrane resulting in the inability to release insulin
when is diazoxide used
for insulomas of the pancreas which causes hyperinsulinaemia
mutations in kir6.2 protein
causes neonatal diabetes resulting in the potassium ATP channel being constantly activated so no cell membrane depolarisation can occur so no insulin can be released , r
