L3 - Endocrine pancreas (L4.1) Flashcards
name of the group of cells in the pancreas
islets of langerhans
4 types of cells part of the islets of langerhans
- alpha
- beta
- delta
- PP cells
what do alpha cells secrete?
glucagon
what do beta cells secrete?
insulin + amylin
what do delta cells secrete?
somatostatin
what do PP cells secrete?
pancreatic polypeptide
describe the structure of insulin
2 AA chains (1 x alpha and 1 x beta)
linked by 2 di-sulphide bonds
intrasubunit disulphide bond in A chain
describe steps of insulin synthesis
- pre-proinsulin produced by ER
- transported to GA
- pre-proinsulin cleaved into proinsulin
- proinsulin cleaved into insulin + c-peptide
what substance is an indicator for the prescence of insulin? why?
c-peptide; as it is produced with insulin
what 3 things control insulin secretion?
- blood glucose
- neural stimulation
- hormones
why is glucose more effect orally than IV?
glucose in the GI tract is digested - GI hormones such as incretins can stimulate b cells to secrete insulin
4 stimulaters of insulin secretion
- parasymapthetic NS
- glucagon
- blood glucose
- GI incretins; GIP and GLP-1
2 inhibitors of insulin secretion
- somatostain
2. sympathetic NS
which vessel is insulin released into? which organ does this go to?
portal vein - liver
why is it better to use c-protein as an indictor for insulin rather than insulin?
c-protein has a much longer half life
how is insulin broken down?
proteolytic degradation
where is insulin broken down?
liver, kidney and muscle
is insulin the only hormone to reduce BG?
yes
2 long term effects of insulin
- increase/decrease key enzymes
2. stimulate cell proliferation
4 effects of insulin in the liver
- increased glycogenesis
- increased glycolysis
- increased lipogenesis
- decreased ketosis and synthesis of ketone bodies
4 effects of insulin in fat
- increased glucose uptake
- increased fatty acid uptake
- increased fat synthesis
- increased glycolysis
4 effects of insulin in muscle
- increased glycogenesis
- increased glycolysis
- increased glucose uptake
- increased uptake of AA
what effect does insulin have on the synthesis of ketones?
decrease
what occurs when the level of ketone bodies increase?
ketone acidosis occurs - turns blood acidic
what causes ketoacidosis?
when only fat is broken down to form glucose - as lack of carbs
how is glucose transported into the cell?
GLUT transporter
what are GLUT tranporters dependent on?
insulin
function of glucagon
increase blood glucose
4 things which glucagon is stimulated by
- AA in plasma
- low conc of glucose + fatty acids
- catecholamines (Ne+E)
- cholinergic stimuli
2 things which glucagon is inhibitated by
- somatostatin
2. high conc of glucose + fatty acids
4 effects of glucagon on carbs
- increase gluconeogenesis
- increase glycolysis
- decrease glycogen synthesis
- dec glucose oxidation
3 effects of glucagon on lipids
- increase lipolysis
- increase ketogeneiss
- dec lipogenesis
1 effect of glucagon on protein
- increase proteolyis
in gluconeogensis, what is new glucose produced from?
proteins, AA, glycerol
when does gluconeogenesis occur?
when there is a limited glucose supply
where is amylin released from?
beta cells
which hormone does amylin complement?
insulin
how does amylin complement the effects of insulin? (3)
- reduce gastric emptying
- antagonising glucagon effects
- reducing food intake
name of amylin drug
pramlintide
function of somatostatin?
imhibit insulin and glucagon release
inhibit release of GI hormones = gastrin, motilin, VIP
a major portion of islets of langerhans consist of what type of cell?
beta
main action of insulin
lower BG
half-life of insulin
3-5 mins
main target tissue for glucagon?
liver
3 main target tissues for insulin?
liver
muscles
fat
name of process: oxidation of glucose to produce energy
glycolysis
name of process:synthesis of glucose from non-carb
gluconeogenesis
name of process: synthesis of glycogen from glucose
glycogenesis
name of process: breakdown of glycogen to form glucose
glycogenolysis
main function of glucagon
increase BG
T/F: insulin promotes glycogenesis
true
T/F: insulin promotes glucose uptake into cells
true
T/F: insulin inhibits ketosis
true
T/F: glucagon promotes gluconeogenesis
true
T/F: insulin inhibits glycogenolysis
true
T/F: insulin inhibits glycolysis
false
T/F: glucagon stimulates glycogenesis
false
what do incretins stimulate?
insulin release from beta cells