insulin and glucose Flashcards
describe insulin processing
- formation of insulin from proinsulin precursor assures that A and B chain are always present in equal amounts
describe familial hyperproinsulinemia
- defects in insulin processing due to mutations in insulin gene
- high proinsulin levels in the blood
- normal glucose metabolism
describe the EVENTS FOLLOWING INSULIN BINDING TO RECEPTOR
- Autophosphorylation of Beta subunits (Tyr)
- Phosphorylation stimulates tyrosine kinase activity of the receptor
- IRS1 (insulin receptor substrate 1) is phosphorylated
- Most of the insulin effects require Ser/Thr phosphorylation
Paradox: receptor activation leads to phosphorylation of signaling proteins and dephosphorylation of metabolic enzymes
describe effects of insulin
- Insluin binding to receptor results in:
- endocytosis of insulin-receptor complex
- translocation of glucose transporter
- Beta-subunit tyrosine kinase activation
- Results in:
- increase foramtion of glycogen
- increased uptake of glucose
- increased utilization of glucose
- decreased foramtion of glucose from glycogen, fat and protein
** DECREASED BLOOD GLUCOSE LEVELS***
describe gestational diabetes
- INsulin sensitivity of the mother decreases to provide glucose to the fetus
- In gestation diabetes mellitus (GDM) is characterized by DECREASED INSULIN SENSITIVITY and inadequate secretion
- decreased insulin receptor kinase activity in GDM
describe the biochem of glucagon
- glucagon ins a peptide hormone which is synthesized in a manner similar to insulin
- synthesized in the ALPHA-CELLS of the pancreatic islets
- Pre-pro-glucagon is proteolytically processed toyeild glucagon
- in contrast to insulin, glucagon does not contain disulfide bridges
describe the effects on liver of insulin vs glucagon
Insulin
–> activates glycogen synthetase
–> stimulates glycolysis and ATP generation
–> no effect on glucose uptake
Glucagon
–> inactivates glycogen synthetase
–> activates glycogen phosphorylase
–> activates glucose-6-phosphatase
–> activates gluconeogenesis
describe the effects on muscle of insulin vs glucagon
Insulin
–> stimulates glucose uptake
–> stimulates glyoclysis and ATP generation
–> increase muscle glyogen and creatine phosphate levels
Glucagon
–> no effect, because there are no glucagon receptors
describe the effects on adipose tissue of insulin vs glucagon
INsulin
–> stimulates glucose uptake
–> promotes glycolysis
–> inhibits lipases
Glucagon
–> no effects, because there are no glucagon receptors
what stimulates insule and glucagon release
describe somatostatin
- somatostatin is a cyclic peptide
- synthesized in the Delta-cells of the pancreatic islets, but also in other organs (hypothalamus)
- Synthesized as pre-pro-somatostatin
describe actions of somatostatin
- Many effects throughout the body
- in pancreas, inhibits the synthesis of both insulin and glucagon
describe the degradation of peptide hormoens
- Half-life of insulin is 3-5 mins
- degraded by receptor-mediated endocytosis
- degradation take place mainly in liver
- 50% of circualting insulin is cleared at the first passage through the liver
- half life of glucagon is 6-7 minutes
- degradation takes place in liver and kidney endosomes
