WEEK 7: 7.3 The Pancreas, Insulin and Glucagon Flashcards
what are the patches of secretory cells on the pancreas called?
Islet of langerhans
What makes up 70% of the cells within the pancreatic islets?
Beta cells
What makes up 20% of the pancreatic islets cells
Alpha cells
What are beta cells?
they secrete insulin, are located primarily in the liver, muscle and adipose tissue, and work to reduce blood glucose
What are alpha cells?
they secrete glucagon, are located primarily in the liver, and work to increase blood glucose
What are the remaining cells that make up the islet of langerhans?
Delta cells
PP cells
what are delta cells
they secrete somatostatin and reduce gastric secretion as well as inhibit digestion of nutrients
what are PP cells
secrete pancreatic polypeptide
Explain the step by step process by which glucose stimulates insulin secretion
- glucose enters B cell through GLUT-2 transporter
- glucose undergoes oxidative metabolism and increased ATP in cell
- ATP dependent K+ channels close due to the rise in ATP, preventing K+ from leaving the cell hence initiating depolarisation
- A shift in voltage from depolarisation causes voltage-sensitive Ca2+ channels to open
- Increase in Ca2+ causes insulin-containing secretory granules to be released into the bloodstream
What factors stimulate the secretion of insulin?
High plasma glucose, gastrointestinal hormones, high free amino acids, parasympathetic stimulation
What factors inhibit the secretion of insulin?
low plasma glucose, sympathetic stimulation, low free fatty acids, somatostatin
Explain in a step by step process, how insulin receptors actually help maintain blood glucose levels?
- when eating food, blood glucose rises, hence body releases insulin
- insulin binds to its enzyme-linked receptor on the surface of target cells (the enzyme is tyrosine kinase)
- tyrosine kinase is activated, and adds phosphate groups to specific tyrosine residues in certain proteins, hence activating those proteins and starting a signal transduction cascade
- signal transduction immediately causes the movement of preformed GLUT4 transporters to the cell membrane
- GLUT4 is stored inside the cell in vesicles (exocytosis)
- more GLUT4 in membrane = more glucose entering the cell
- blood glucose decreases
What are glucose transporters not regulated by insulin?
GLUT1
GLUT 2
GLUT 3
Explain the step by step process in which insulin helps store energy for later
- after eating, there is increased glucose in the blood, and the pancreas releases insulin in response
- insulin binds to receptor on liver cells and activates signal cascade
- glut2 transporter helps glucose enter the liver cell from blood
- glucose quickly turned into G6P using ATP
- G6P is converted into glycogen
Summarise the action of insulin in terms of protein
- promotes active transport of amino acids into muscle
- increases protein synthesis
summarise the action of insulin in terms of fats
- increase fatty acid uptake into adipose
- increases fatty acid synthesis from glucose into adipose
- decrease lipolysis in adipose
summarise the action of insulin in terms of carbohydrates
- facilitate glucose uptake and utilisation
- stimulate glycogenesis and inhibit glycogenolysis
- increases conversion of glucose to fatty acids in adipose cells
- inhibit gluconeogenesis
What stimulates the secretion of glucagon by alpha cells?
low plasma glucose
sympathetic stimulation
high free amino acids
low free fatty acids
what inhibits the secretion of glucagon in alpha cells?
high plasma glucose, insulin somatostatin, high free fatty acids and ketoacids
What are the primary actions of glucagon
- binds to receptors on liver cells, activating a signaling cascafe that causes glycogen to break down into glucose (glycogenolysis)
- inhibits protein synthesis and promotes protein degradation
- promotes fat breakdown and inhibits triglyceride synthesis
- increase in blood levels of fatty acids and ketones
What is involved in type 1 diabetes mellitus
- destruction of beta cells (auto immune response)
- no insulin secreted (high glucose concentration)
- chronic fasted state, ketoacidosis, glucosuria, polyuria, polydipsia
- lead to coma and death
What is involved in type 2 diabetes mellitus
- gradual progressive development of insulin resistance
- common in older and overweight individuals
- large genetic component
