Pancreas Flashcards
where does the pancreas develop from?
- foregut : coeliac trunk
- midgut : superior mesenteric
- hindgut : inferior mesenteric.
*pancreas if an outgrowth of the foregut.
what are the functions of the pancreas?
HINT : exocrine and endocrine
- exocrine : produce and secrete digestive juices directly into duodenum. (alkaline secretions)
- endocrine : hormone production from islets of langerhans located close to blood supply.
name some important hormones secreted by the pancreas.
- insulin.
- glucagon.
- somatostatin.
- ghrelin.
what are the major cell types in islets and what do they secrete? what function do they serve?
- alpha cells : glucagon - raises blood glucose, catabolic.
- beta cells : insulin - lowers blood glucose, anabolic.
what is the importance of blood glucose levels?
- brain uses glucose at fast rate and relies on blood for supply.
- sensitive to falls or rise.
what is the significance of insulin and glucagon being water soluble?
- able to be carries in plasma without special proteins.
- short half life allows ability to react quickly to dynamic environment.
describe the structure of insulin.
- large peptide with alpha helical structure, 2 unbranched pp chains connected 2 disulphide bridges for stability
how is insulin synthesised?
- pre-proinsulin translated, cleaved and folded into proinsulin at RER.
- proinsulin to golgi, c-protein cleaved off and then turned to insulin and secreted in granules.
- marginised and exocytosed with calcium signals.
what is the significance of c-peptide?
- type 1 diabetes who lack C-peptide shown improvements with c-peptide treatments as diminished glomerular hyperfiltration, reduced urinary albumin excretion and improved nerve function.
- important in suspected insulin overdose deaths, if insulin>c peptide seen then external insulin high.
k+
DDD
how is insulin secretion regulated?
- with feeding and rise in glucose there is a rise in ATP:ADP ratio.
- ATP inhibits K+ATP and reduced K+efflux.
- membrane depolarises activated voltage dependent Ca2+ channel and raise in intracellular calcium.
- triggering exocytosis of insulin vesicles.
what systemic effects does insulin have?
- increases glucose uptake and glycogen synthesis.
- liver increases glycogen synthesis.
- muscles increase uptake of AA and increases protein synthesis.
- liver inhibits AA breakdown.
- adipose increases TAG storage.
- FA breakdown inhibited.
describe the structure of the insulin receptor?
- dimer of two subunits of alpha and beta chains connected by a disulphide bond.
- alpha exterior of cell membrane and beta span across membrane.
what are the effects of glucagon?
- opposes insulin by raising glucose levels in blood.
- glycogenolytic, gluconeogenic, lipolytic, ketogenic.
- mobilises energy release.
how is glucagon synthesised and secreted?
- in RER and transported in golgi.
- packages in granules are effect on liver.
- secreted by alpha cells, secreted at low glucose levels in alpha cells.
- similar K-ATP mechanisms as beta cells seem to be involved in secretion.
describe the structure of glucagon.
- 1 PP chain, no disulphide as structure already flexible.
- simpler precursor and undergoes post-translational processing.
what are the effects of glucagon?
- liver increases rate of glycogen breakdown (glycogenolysis).
- stimulates synthesis of glucose from AA (gluconeogenic).
- stimulates lipolysis to increase plasma FA.
clinically whats the significance of glucangon?
- in emergency medicine when person with diabetes is experiencing hypoglycaemia and cannot take sugar orally.
what are the terms used to describe abnormal levels of insulin or glucagon?
- high insulin : hypoglycaemia.
- low insulin : hyperglycaemia/ diabetes mellitus.
- high glucagon : makes diabetes worse.
- low glucagon : hypoglycaemic effects.
what causes type 1 diabetes and what is it?
- resistance or deficiency in insulin.
- absolute due to autoimmune destruction of pancreatic B-cells.
- relative if secretory response impaired.
what causes type 2 diabetes and what is it?
- relative peripheral insulin resistance.
- defective receptor mechanism and change in receptor number or affinity.
- excessive glucagon amounts.
why might insulin resistance be seen in young?
- onset of hyperglycaemia and develop type 2.
- initially : B cells compensate by increasing insulin.
- eventually : unable to maintain high production.
- finally : B-cells dysfunction leads to relative insulin deficiency.
