Metabolism - The Pancreas Flashcards
What cells present in the pancreas produce what hormone?
Alpha cells - glucagon Beta cells - insulin Delta cells - somatostatin F cells - PP (GI function) Other cells - Ghrelin
What are the 2 hormonal functions of the pancreas?
Exocrine secretion of digestive enzymes into duodenum (and of alkaline secretion via pancreatic duct)
Endocrine secretion of hormones from islets of Langerhan into bloodstream.
Where does the pancreas develop from?
An outgrowth of the foregut embryologically.
What is insulins structure?
2 chains held rigid by 2 disulphide bonds
How is insulin synthesised?
1) . Produced initially as preproinsulin, but pre is cleaved via signal peptidase upon entry to the ER lumen.
2) . Proinsulin is exposed to endopeptidases, which cleave the C peptide = insulin and C peptide.
3) . These are packaged together into vesicles in the Golgi.
What is margination?
It is the movement of secretory vesicles to the surface of the cell.
How is insulin secreted?
1). High glucose levels are detected in extracellular fluid = insulin needs to be released.
2). Glucose enters the beta cell by facilitated diffusion through GLUT2, as there is a slight conc gradient from the blood
= depolarises membrane
3). This causes an influx of Ca2+ ions as Ca2+ channels open, triggering exocytosis of vesicles.
4). Beta cells are close to capillaries, so upon the signal, vesicles fuse to the cell membrane, and release their contents on the other side, into the capillary.
5). More vesicles are made to replenish the store of those lost..
What is the structure of an insulin receptor?
1 alpha chain on top of the membrane, and 1 beta chain spanning the membrane below, held together by a disulphide bond.
How does insulin act upon its receptor?
It binds to the extracellular alpha chain, which causes a conformational change in the beta chain.
This activates tyrosine kinase, which initiates a phosphorylation cascade of reactions which result in the expression of more GLUT 4 channels in the cell
= more glucose can enter.
What is the effect of insulin in muscle?
Increased take up of glucose = more respiration.
Increases amino acid take up = greater protein synthesis
DUE TO INCREASED GLUCOSE UPTAKE VIA GLUT 4
What are the effects of insulin in the liver?
It inhibits breakdown of proteins
It stimulates glycogen synthesis
DUE TO INCREASED GLUCOSE UPTAKE VIA GLUT 4
What are the effects of insulin on adipose tissue?
Inhibits beta oxidation
Increases storage of TAGs
DUE TO INCREASED GLUCOSE UPTAKE VIA GLUT 4
What is the structure of glucagon?
A small, single polypeptide chain made flexible by its lack of disulphide bonds.
How is glucagon secreted?
When glucose is low, this is detected by alpha cells which as a result produce glucagon.
This is packaged into vesicles then secreted via marination and exocytosis.
What are the effects of glucagon in the liver?
Stimulates gluconeogenesis (often amino acids to glucose) and glycogen degradation
Inhibits glycogen synthesis
