lecture 24 Flashcards
what does blood glucose homeostasis require?
effective regulation
(usually driven by insulin and glucagon)
what occurs to blood glucose after a meal?
-increase
-comes down with time
what occurs to insulin with low blood glucose levels?
insulin levels low
what occurs to insulin with high blood glucose levels?
insulin levels also high
what is hyperglycaemia?
blood glucose levels are too high
what does hyperglycaemia cause?
high blood glucose to stimulates insulin secretion
what occurs with hyperglycaemia and glucagon?
inhibits glucagon secretion
when is glucagon at highest?
when glucose levels are low
what is the role of insulin?
-secreted in conditions of high blood glucose
-insulin decreases blood glucose levels to normal range
what is the role of glucagon?
-secreted in conditions of low blood glucose
-increases the blood glucose levels
what occurs after a meal?
-increase blood glucose levels
-signals pancreas to release insulin
-insulin is signal to decrease blood glucose levels
where is the signal sent to?
liver, adipose tissue and muscle
what does the insulin signal mean?
increase glucose uptake, don’t produce any more glucose, form glycogen with the insulin
what occurs after exercise/prolonged periods of not eating?
-blood glucose decreases
-pancreas detects the change and releases glucagon
-glucose levels increased to normal range
where does the glucagon act upon?
liver
what are the main functions of the liver?
- exocrine - releases digestive enzymes into gut
- endocrine - blood glucose homeostasis
what are the pancreatic islets (islets of langerhans)?
-scattered throughout pancreas
-comprise of alpha, beta and delta that secrete hormones
-small and different
-regulate blood glucose
what do the pancreatic alpha cells release?
glucagon
what do the pancreatic beta cells release?
insulin
what do the pancreatic delta cells release?
somatostatin
what are the regulators of insulin release?
glucose
amino acids
gut hormones
neural input (cholinergic)
adrenaline (inhibitory action)
somatostatin (inhibitory action)
what are the regulators of glucagon release?
glucose (inhibitory action)
insulin (inhibitory action)
amino acids
neural input (stress)
adrenaline
cortisol
gut hormones (inhibitory action)
how is insulin produced by pancreatic beta cells? complex
-gene transcription produces unfolded structure
-needs to be folded so transported to ER
-forms preproinsulin (has n terminal signal peptide, beta chain of insulin connected to a chain)-not active
-cleaved to proinsulin
-transported to Golgi (packages proteins)- production off disulphide bonds between b and a chains
-cleavage of c peptide forming mature insulin
how is insulin formed? simple
-produced in islet beta cells as pre-proinsulin
-intramolecular disulphide bonds formed between b and a chains, cleaving a C-peptide (inactive) and insulin