The Pancreas Endocrine Function Flashcards
What types of hormones are produced in the pancreas and where are they produced
Polypeptide hormones
Islets of Langerhans
What is the structure of insulin
Two polypeptide chains with two disulphide bonds covalently linking them
How can we test for any endogenous insulin secretion
Measure plasma C-peptide
How is insulin produced in beta-cells
Synthesised as pre-proinsulin and then enters endoplasmic reticulum where signal peptide, the pre part, is removed
Proinsulin is folded to ensure correct alignment of cysteine residues and is then transported to trans-golgi
It is packaged into storage vesicles and then undergoes proteolysis to removed connecting C-peptide, forming insulin
Storage vesicle then marginates to cell membrane
How is insulin released from cells
Glucose enters cell via GLUT-2 and is metabolised to produce ATP
Increase in ATP close KATP channels in B-cell preventing K efflux
This depolarises the membrane, opening Ca channels
Ca enteres the cell causing the storage granules to fuse with the membrane and release their contents
What are the major actions of insulin on metabolism
Increase glucose uptake by adipose and skeletal muscle (GLUT-4 channels inserted)
Increase glycogenesis and decrease glycogenolysis in liver and muscle
Decrease gluconeogenesis in liver
Increase glycolysis in liver and adipose
Decrease lipolysis in adipose
Increase lipogenesis and esterification of fatty acids in liver and adipose
Decrease ketogenesis in liver
Increase lipoprotein lipase activity in tissues
Increase amino acid uptake and protein synthesis in liver, muscle and adipose
Decrease proteolysis in liver, skeletal muscle and adipose
What are the problems associated with abnormal levels of insulin and glucagon
Insulin
- High - hypoglycaemia
- Low - hyperglycaemia and diabetes mellitus
Glucagon
- High - makes diabetes worse
- Low - possibly contributes to hypoglycaemia
What factors increase and what factors decrease insulin secretion
Stimulate - metabolic signals, GI tract hormones, acetyl choline
Inhibit - adrenaline, noradrenaline
Describe the glucogen molecule and where it is produced
Single chain polypeptide
Lacks disulphide bonds and has a felxible 3D shape - takes up its active conformation on binding to its receptor
Produced by a-cells in Islets of Langerhans
What factors control glucagon secretion
Stimulated by low plasma glucose
Inhibited by insulin and high/increase in plasma glucose
What are the actions of glucagon
Increase glycogenolysis in liver
Increasde gluconeogenesis in liver
Decrease glycogenesis in liver
Increase ketogenesis in liver
Increase lipolysis in adipose
When is glucagon used clinically
When a person with diabetes is experiencing hypoglycaemia and cannot take sugar orally
What is the normal range of plasma glucose and what can it rise to after eating
- 3-6.0mmol/L normally
- 0-8.0mmol/L after a meal
