Insulin and Glucagon Flashcards
how long would plasma glucose last? glycogen? fat?
1 hour
part of one day
40 days with water
how much protein is in the body and how much of it could be use for energy needs?
10-12 kg
1/2 is available
what is the normal blood concentration of glucose?
80-100 gm/dL
what is the role of somatostatin in the pancreas?
prevents release of insulin and glucagon
what is the brain energy source? how much oxygen does it require?
glucose
20% of resting oxygen supply
what are the three types of islets of langerhans cells and what do they secrete?
alpha- glucagon
beta- insulin
delta- somatostatin
where is pancreatic polypeptide secreted? what does it do?
GI hormone synthesized by F cells at the periphery of the islet (with alpha and delta cells)
inhibits gallbladder contraction and pancreatic exocrine secretion
when is pancreatic polypeptide secreted?
during strenuous exercise, after ingestion of a protein rich meal or during hypoglycemia
how is glucagon synthesized?
it is translated as pre-proglucagon and processed postranslationally into glucagon, glicentin, GLP-1 and 2 and glicentin- like peptide
stored in membrane bound granules
what happens to glucagon after it is released?
it is degraded by the liver and kidney (not excreted)
what are stimulators of glucagon secretion?
hypoglycemia <50mg/dl
increase in arginine and alanine (protein degredation)
exercise and stress
what are three inhibitors of glucagon secretion?
insulin, somatostatin and hyperglycemia
what are the counter regulatory hormones? what do they do?
glucagon, catecholamines, growth hormone and cortisol
keep blood glucose high enough for brain
what is the primary target of glucagon? what does it do?
liver
increases blood glucose- glycogenolysis, gluconeogenesis, and lypolysis
what does glucagon do in adipose tissue?
decreases glycolysis and promotes release of fatty acids
how is insulin synthesized?
synthesized in perproinsulin form
processed in storage granules with endopeptidase (secreted together)- cleaved into insulin and C peptide
why is zinc included in secretory granules?
to join 6 insulin molecules into hexamers
what are levels of C peptide used for?
to quantitate endogenous insulin production when patients receive insulin injections
what type of insulin is used to inject to diabetic patients?
crystalline zinc insulin
how is insulin degraded?
insulinases in liver, kidney and other tissues
describe postprandial insulin secretion.
there is an early phase of insulin release after 10 min and a peak at 30-45 min (late phase)
describe release of insulin with IV glucose.
early phase (release of stored insulin) which falls in 10 min late phase if stimulus is maintained- reflects newly formed
what is the mechanism of insulin secretion from beta cells?
1 GLUT 2 transporter mediates diffusion of glucose in
2 increase in ATP due to glucose metabolism
3 ATP inhibits a K channel-cell voltage increase
4 depolarization activates Ca channel and Ca induced Ca release
5 elevated Ca leads to fusion of vesicles- insulin release
besides glucose, what else can modulate insulin secretion?
amino acids, other monosaccharides, and certain hormones
describe the phases of digestion with respect to insulin.
cephalic phase- vagus mediates small rise in insulin
intestinal phase- glucose absorption stimulates secretion
what do incretins do?
provide advance notice of feeding and stimulate insulin secretion
CCK, GIP and GLP-1 increase insulin during feeding
describe the effects of epinephrine and NE on beta cells.
epinephrine- stimulates secretion (beta receptor)
NE- supresses insulin (alpha receptor)- from postsynaptic nerve terminals
what is the net effect of sympathetic action on beta cells?
there is a net supression of insulin secretion
what is insulin’s effect on the liver?
stimulates glucose uptake, glycogenesis, lipogenesis, glycolysis and protein synthesis
what is insulin’s effect on myocytes?
stimulates glucose uptake with increase GLUT 4 on surface, promotes glycogenesis and glycolysis
also stimulates lipogenesis and protein synthesis (AA uptake also)
what is insulin’s effect on adipocytes?
increase in GLUT 4 and LPL export to capillaries. also increases glycolysis and esterification of fats
what is the difference in results of a glucose tolerance test with diabetes?
plasma glucose will rise higher and remain there longer
what disease causes insulin deficiency? insulinemia? glucagon deficiency?
type 1 diabetes
insulin shots and insulinoma
glucagon deficiency very rare
what are orixigenic factors? give an example
neurotransmitters that stimulate feeding
neuropeptide Y
what are anorexigenic factors? give 4 examples
neurotransmitters that inhibit feeding
GLP-1, corticotropin releasing hormone, alpha MSH and CART
what do satiation sinals do?
secreted in response to food ingestion, act within timeframe of single meal and reduce meal size
where is the primary control of food intake?
hypothalamus
which GI peptides reduce meal size?
CCK, GLP-1, GLP-2, glucagon, and PYY
what pathway carries information that fat and protein has been eaten?
nucleus of the solitary tract
where is ghrelin secreted and what does it do?
secreted from oxyntic glands of stomach
stimulates food intake by acting on arguate nucleus to increase NPY and inhibit CART
what hormones are secreted in proportion to the amount of fat in the body?
leptin and insulin- enter hypothalamus to influence energy homeostasis
what contributes to meal onset signals and what do they activate?
environmental factors, low leptin, hypoglycemia, hypoinsulinemia and negative energy balance
activate orexin and MCH expression
what strategies need to be devised for long term weight loss success?
counteracting hormonal changes to weight loss that stimulate appetite
