L13 - the endocrine pancreas Flashcards
The pancreas is a large gland which develops as an outgrowth of the foregut. Explain briefly its two functions
Exocrine - produces digestive enzymes which are secreted directly into the duodenum from cells in the islets of langerhans
Endocrine - produces insulin and glucagon from beta and alpha cells of the islets of langerhans respectively amongst others which are then secreted into the bloodstream when necessary
what blood sugar state stimulates glucagon production?
low blood sugar
Describe briefly how insulin and glucagon mediate their effects
insulin - upregulates glucose transporters in adipose and muscle cells thus increasing glucose uptake from the blood and causing glycogenesis
glucagon - stimulates glycogenolysis in the liver and gluconeogenesis thus increasing plasma glucose levels
glucagon only works on liver and adipose tissue whereas insulin also acts on skeletal muscle, T or F?
T
What is the normal reference range for plasma glucose? Will this rise or fall after a meal?
3-3.6mmol/L
Rise
briefly describe the structure of insulin
an alpha and beta chain linked by disulfide bridges and a C peptide
Describe briefly how vesicles of insulin and C-peptide
insulin mRNA translated into pre-pro form by the RER -> cleavage to proinsulin in the RER and transportation to the golgi -> clevage to insulin and C peptide in the golgi -> placed in vesciles awaiting signal at beta cell plasma membrane
Explain briefly how the vesicles of insulin and C peptie are signalled for release
high plasma glucose levels cause ATP sensitive K+ channels to shut on the plasma membrane of beta cells -> potassium builds up in the cell causing a depolarisation -> depolarisation triggers the opening of voltage gated calcium channels -> calcium moves in down it’s gradient and triggers the release of the insulin and C peptide vesicles
What are the major metabolic effects of insulin?
-Increases glucose uptake via insertion of glut 4 channels/ increases glycogenesis/increases protein synthesis/inhibits breakdown of amino acids/increases fat storage
what class of receptor is the insulin receptor?
A receptor tyrosine kinase
What are the metabolic effects of glucagon?
stimulates glycogenolysis/gluconeogenesis/lipolysis/inhibits protein synthesis/inhibits amino acid uptake
When is glucagon given in an emergency?
In a diabetic hypoglycaemic episode where the patient can’t take sugar orally
Which channel is the most commonly mutated in type 1 diabetes?
GOF mutation in Kir6.2 (ATP sensitive K+ channel) - remains open and thus insulin can’t be released - idea that it is open at rest but closes when signal (high plasma glucose) comes causing depolarisation
What channels does insulin cause the translocation of?
GLUT4 channels
How is the structure of the beta cell adapted to synthesis and storage of insulin. Briefly exaplin the synthesis too.
Synthesis - Pre-proinsulin is cleaved to pro-insulin in the RER -> proinsulin transported to golgi -> proinsulin cleaved to insulin and C-peptide in the golgi which are packaged into vesicles where they await a signal at the plasma membrane
adaptations
- lots of RER, golgi and vesicles
