hormonal regulation of metabolism Flashcards
effect of pancreatic insulinoma
increases insulin production, leads to fasting hypoglycemia
action of insulin
stimulates glucose uptake into tissues for use and storage
steps of insulin synthesis
made in RER of pancreatic b-cells
- initial form is preproinsulin, this is converted to proinsulin by cleaving the signal sequence
- proinsulin is transported to golgi
- proinsulin is converted to insulin by cleaving C-peptide
- end product = a chain and b chain linked by 2 disulfide bonds
describe the biphasic release of insulin
initially, insulin levels increase rapidly bc the insulin that was stored in b-cell secretory vesicles is released, sustained insulin response is from de novo synthesis and is more steady
typical insulin level at fasting blood glucose
usually 1
to what blood glucose level can insulin accommodate
insulin will continue to rise with blood glucose until about 300 mg/dL, past that insulin will remain steady even if glucose continues to rise
stimulatory effects of insulin (5)
uptake of glucose into (some) tissues use of glucose fat synthesis fat storage general protein synthesis
inhibitor effects of insulin (2)
glycogen breakdown
fat mobilization
major glucose transporter in muscle and adipocytes
GLUT-4
effect of insulin on the liver
stimulates use of glucose (like glycogen synthesis and glycolysis), but does NOT direct glucose uptake
what is the action of glucokinase in the liver?
insulin stimulates glucokinase in the liver, action of glucose kinase is to phosphorylate glucose to effectively trap it in the liver
which type of cells discussed use insulin-indpendent methods of glucose uptake?
neural cells
normal vs. abnormal response to glucose tolerance test
normal- rapid rise and drop in blood glucose, hypoglycemia may result, blood glucose should return to around fasting by 3 hrs
abnormal- higher and more sustained increase in blood glucose level
glycemic index
area under 2 hr glucose curve after feeding a 50 g test CHO portion
what is the “standard for GI”?
white bread, GI = 1.0
ways to increase GI
refine, make more simple sugars
ways to decrease GI
add fiber, fat, protein
glucagon source and structure
pancreatic a-cells
proglucagon = 160 aa
mature form = 29 aa
short half life in plasma
what will stimulate glucagon secretion? (4)
- low blood glucose
- epinephrine
- cortisol
- exhaustive exercise
what inhibits glucagon secretion? (2)
high insulin
high glucose
what does glucagon act on directly?
liver and adipocytes
what can glucagon not act on directly?
muscle, bc it lacks glucagon receptors
what does glucagon stimulate? (3)
- glycogenolysis in liver
- breakdown of TAG in adipocytes to fatty acids and glycerol
- breakdown of protein in muscle to provide aa for gluconeogenesis
what does glucagon inhibit? (2)
glycogen synthesis
fat storage
what hormone stimulates glycogen mobilization in muscle?
epinephrine
what is the result of glucogenolysis in muscle?
glucose is phosphorylated and muscle lacks the phosphatase needed to remove phosphate, so it remains in the muscle where it is used for energy. Byproducts of glucose metabolism (lactate and pyruvate) can be used in gluconeogenesis
which tissues are acted on by epinephrine?
liver, adipocytes, muscle
what is the effect of epinephrine on glucagon? insulin?
glucagon- stimulates release
insulin- inhibits release
which tissue lacks glucagon receptors?
muscle
which tissues are acted on by glucagon?
liver, adipocytes
what signaling pathway is common for epinephrine and glucagon?
both use GaS, increase cAMP and activate protein kinase a
what is activated by protein kinase A?
what is inactivated by protein kinase A?
activated- glycogen phosphorylase, lipase
inactivated- glycogen synthase, fatty acid synthesis
how does cortisol stimulate fuel mobilization?
binds to intracellular receptors and regulates gene transcription
what is unique about the action of cortisol?
it is released in times of stress, but it stimulates glycogen synthesis NOT breakdown
insulin vs protein kinase a
insulin will activate serine/threonine phosphatase that will oppose the actions of PKA- will turn on glycogen synthase/fatty acid synthesis and turn off glycogen phosphorylase and lipase
describe hormone changes after protein only meal
- increase glucagon- amino acids alone stimulate glucagon release bc glucagon will stimulate amino acid degradation and gluconeogenesis in the liver
- increase insulin slightly to promote uptake of amino acids into muscle and stimulate protein synthesis
in “mixed” meals, which 2 aa in particular, will stimulate insulin release in response to glucose?
lysine
arginine
