Blood Glucose Hormones Flashcards
what are the hormones that raise blood glucose?
glucagon
cortisol
catecholamines (epinephrine, norepinephrine)
growth hormone
What are the hormones that lower blood glucose?
insulin
what cells secrete insulin?
beta cells in core of pancreatic islets of langerhans
what cells secrete glucagon?
alpha cells on the edges of pancreatic islet of langerhans
what cells secrete somatostatin?
delta cells in pancreatic islet of langerhans
describe the structure of insulin
contains an alpha and beta chain held together by two S-S bridges.
A chain contains six membered ring
entire molecule except for carboxyl end of B is required for biological action
insulin is conserved across species
ok
describe the biosynthesis of insulin
synthesized in beta cells.
preproinsulin has a signal sequence cleaved off, forming proinsulin.
proinsulin is cleaved of C-peptide to form insulin
how do you measure endogenous insulin production
measure amount of C-peptide
describe how beta cells sense blood glucose
glucose is transported into beta cells via GLUT2, and glucokinase converts it into glucose-6-phosphate
this begins glucose metabolism, which increases the ATP/ADP ratio, which inhibits ATP-sensitive K channels. This depolarizes the membrane and activates voltage gated Ca channels, leading to exocytosis of insulin
leads to increase in insulin production, secretion, storage, and beta cell proliferation
how do amino acids affect insulin secretion?
esp arginine
increase insulin secretion, especially in combo w/ glucose
how do ketones affect insulin secretion
stimulate insulin release
why is glucose through the gut more effective than through IV
b/c it stimulates glucagon-like-peptide 1, which stimulates insulin release
what are the effects of catecholamines on insulin release?
depends what receptors they use
a-receptors- more common- result in inhibition of insulin release
b-receptors- less common- results in stimulation of insulin release
what is the effect of somatostatin release?
potent inhibitor of insulin and glucagon release
insulin degradation
insulin half life is only 10 minutes
kidney and liver account for 80% of degradation
describe the insulin receptor
a tyrosine kinase comprised of
an alpha-beta heterodimer, the alpha portion is the binding unit and the beta unit is a transmembrane effector protein
the complex is ultimately internalized, where insulin is degraded but the receptor is recycled
what are the actions of insulin on muscle?
glucose uptake- cause GLUT4 receptors to be translocated to membrane
glycogen synthesis- glycogen synthetase is inactive when phosphorylated. insulin activates a phosphatase to remove the P, and inactivates glycogen synthase kinase-3
amino acid uptake
protein synthesis
inhibits proteolysis
what are the effects of exercise or anoxia on glucose uptake?
these stimuli allow for glucose uptake w/o insulin
what are the effects of insulin in adipose tissue?
glucose uptake- causes GLUT4 receptors to be translocated to membrane
fat synthesis
lipoprotein lipase synthesis- breaksdown lipoproteins (chylomicrons and VLDL) for uptake into adipose
inhibits HS lipase- breaks down triglyceride inside adipose
glycogen synthesis
AA uptake and protein synthesis
effects of insulin on liver
stimulates glucokinase and glycogen synthease
stimulation of phosphofructokinase, pyruvate kinase, pyruvate dehydrogenase (glycolytic rate limiting enzymes)
inhibits gluconeogenic enzymes (glucose-6-phosphatase, fructose-1,6-diphasphatase, PPCK, pyruvate carboxylase)
stimulates fatty acid synthesis
describe GLUT2
the glucose transporter in the liver and pancreas, can handle a wider range of glucose concentration than GLUT4, and so transport is not limited
is not upregulated by insulin
where does glucagon exert its effects?
liver
what factors control secretion of glucagon
low blood sugar- primary
amino acids - esp arginine
catecholamines
sympathetic innervation
inhibited by somatostatin
