Endocrine Pancreas Flashcards
What is insulin made up from?
A chain with 21 aa
B chain with 30aa
C chain 31aa (pro insulin)
How is insulin synthesised?
Insulin gene transcription and translation. Preproinsulin synthesis in RER ( cleavage of signal sequence).
Micro vesicles transfer pro insulin. Pro insulin to insulin in Golgi by cleavage of c- peptide.
In secretory granules insulin precipitates into dense crystalliod core with a ratio of 2 zinc ions to 6 insulin. The. Exocytosis involve ca2+ and ATP
What 3 enzymes are used to convert pro insulin to insulin?
Proconvertase 1
Proconvertase 2
Carboxypeptidase H
How is insulin release regulated by nutrient stimuli?
Regulated by glucose. Basal level of insulin release occurs at low blood glucose levels. When blood glucose above 5mM - rise in ATP:ADP ratio results in closure of ATP sensitive k+ channels, membrane depolarisation, leading to opening of voltage gated ca2+ channels leading to insulin release .
What other things regulate insulin release?
Potentiators like GLP-1
Neural control
What are the 4 mains actions of insulin?
Promote growth and development
Promote cellular uptake of K+ via Na+-K+ ATPase pump
Promote uptake and utilisation of glucose in skeletal muscle and adipose
Promote fuel storage (anabolic)
Increase rate of synthesis and storage of energy reserves and of protein.
Does insulin reduce blood glucose and what is the mechanism of insulin receptor signalling?
Yes
Intrinsic tyrosine kinase activated by hormone binding
Tyrosine phosphorylation of receptor
adaptor proteins recognise the phosphorylates receptor and produce multiple signals, including gene expression changes
What sort of protein is somatostatin, how many AAs is it made up from and where it is synthesised?
What does somatostatin inhibit?
Peptide hormone
14aa
Synthesised on islet delta cells and CNS and GiT
inhibits glucagon and insulin secretion
What type of hormone is glucagon, how many AAs is it made from? When is it released and inhibited?
Peptide
29
Released by low blood glucose
What are the main actions of glucagon?
Stimulate hepatic glycogenolysis
Stimulate hepatic gluconeogenesis
Stimulate lipolysis
What is released during severe and prolonged hypoglycaemia?
Severe - adrenaline
Prolonged - cortisol, growth hormone
What is the islets of langerhans composition?
Alpha cells make glucagon
Beta cells produce insulin
Delta cells make somatostatin
PP make pancreatic polypeptide
Epsilon make ghrelin
