Define the pancreas?
Which has both exocrine and endocrine cells
Located behind the stomach.
Secretes into a duct
Secretes directly into the blood stream
What are the cells in the pancrease that produce exocrine product?
Produce an enzyme-rich juice used for digestion
What is the name for the cells that produce endocrine products?
Islets of langerhans.
Produce hormones involved in regulating fuel storage and use.
What are the key parts of the pancreas?
Pancreatic duct (goes into the lumen of the gut)
Pancreatic acinar cells
the different cells in the Islets of Langerhans?
Beta cells: produce insulin
alpha cells: produce glucagon
Delta cells: produce somatostatin.
F cells: produce pancreatic polypeptide.
The location in the pancreas of the cell types?
Consisting of two amino acid changes linked by disulfide bonds.
Produced as pro-hormones first until they reach the site of action.
Why are enzymes synthesised as pro-enzyme instead of active enzyme?
So the do not digest the cells they are manufactored in.
eg. if insulin were to be active it would digest the pancreatic cells.
DNA (in beta cells) ->
Preproinsulin (contains an addition polypeptide sequence at the N-terminal) --->
Insulin synthesis and release?
mRNA binds to preprohormone.
Enzymes in the ER remove the signal sequence producing prohormone.
Prohormone passes from ER to Golgi apparatus.
Secretory vesicles contain enzymes and prohormones making hormone.
Hormone is released into the extracellular space
What effects the synthesis of insulin?
Glucose or feeding
Decreased by fasting
What is the threshold of glucose-stimulated insulin secretion?
How does glucose stimulate insulin secretion?
GLUT2 uptakes glucose into the beta cells.
Glycolysis- increase in ATP.
ATP-sensitive potassium channel- inward movement of potassium.
Depolarisation of the cell.
Inward calcium movement: by voltage-gated calcium channel.
This calcium stimulates the release of the insulin vesicles.
Regulators of insulin secretion?
Increase in serum glucose.
What level of plasma glucose when no insulin is produced?
What level of plasma glucose when half-maximal insulin response occurs?
What level of plasma glucose conc when a maximum insulin response occurs?
Insulin is biphasic?
It has two phrases of production
upon glucose stimultion: initial burst.
second phase: gradual increment. Lasts as long as blood glucose levels are high
Graph representing the insulin secretion?
Peak straight after increase in glucose levels.
Potent hyperglycemic agent.
Produced by alpha cells in the pancreas
What does glycagon target and what does it promote?
Major target is the liver.
Promotes glycogenolysis: breakdown of glycogen to glucose.
Gluconeogenesis: synthesis of glucose from lactic acid.
Release of glucose to the blood from liver cells.
DNA in alpha cells
Factors affecting glucagon secretion?
decrease in blood glucose, Increase in serum amino acid, stress and exercise.
SS, Insulin, increase in blood glucose
What kind of feedback happens on glucagon when the plasma glucose increase?
Negative feedback onto the alpha cells
Decreases the glycagon levels
Insulin and Glucagon together?
A balancing act.
Levels of glucose in blood low: glucagon needed.
Level of glucose are high: insulin needed.
Secreted by delta cells.
Released to same stimuli as insulin.
Pancreatic polypeptide hormone?
Secreted by the F cells
Release in response to the high protein meal, low blood sugar and stenous exercise.
Inhibits gall bladder and pancreatic exocrine secretion.