regulation of blood glucose Flashcards
blood glucose concentrations are regulated tightly b/w ___ and ___
70-180 mg/100 mL of blood
the low end (70) is set by ____
the metabolic requirements of impt tissues (by nervous system and brain)
brain does not synthesize and store glycogen, it depends on constant supply of glucose from blood to maintain high metabolic activity –> glucose crosses blood-brain barrier by way of glucose lung transport
the high end (180) is set by ___
ability of nephron to reabsorb glucose back into blood normally, proximal covoluted tubule reabsorbs 100% of glucose, but b/c they have active sites that can be saturated, there is a max rate at which they can reabsorb glucose (if gluc conc gets too high, active sites saturated & glucose lost in urine) – Tmax, when blood glucose gets above 180mg –> lost in urine
hormonal regulation of blood glucose is by:
insulin & glucagon
insulin regulates the ___ end of blood glucose concentrations –> insulin is secreted from ___ cells…
how long is its half life
high end
beta cells of pancreatic islets - it is a peptide, synthesized in rough ER as preprohormone –> signal sequence cleaved
insulin has short half life in blood (5 mins)
what is the signal for secretion & production of insulin?
high blood sugar –> insulin functions to promote glucose uptake by liver –> works rapidly thru second messenger cyclic AMP and phosphorylation of glucose transporters –> more glucose uptake and glycogen synthesis
insulin binds to ___ receptor…
insulin receptor (tyrosine kinase receptor), a dimer of identical alpha & identical beta chains –> alpha chains on surface where insulin binds, beta chains have tyrosine kinase activity, they put a phosphate on the tyrosine chain –> 3 phosphates on the beta chain, beta chain basically phosphorylates itself and reciprocally to each other –> phosphorylation activates receptor, TKR begins to phosphorylate downstream receptors –> ultimately, get phosphorylation of glucose transporters and insert them into membrane to allow greater uptake of glucose
glucagon responds to what signal?
glucagon secreted by ___ cells
low blood sugar (below 70)
alpha cells of pancreatic islets, is a peptide –> synthesized as prohormone
glucagon’s primary target is the ___ and its major effect is…
what is its mechanism?
liver (where all stored glycogen is), converts glycogen back to glucose and release glucose into bloodstream to raise blood glucose back to normal
glucagon binds to glucagon receptor on surface –> activates G proteins to activate adenylate cyclase –> ATP to cyclic-AMP –> activates protein kinase A –> ultimately converts glycogen to glucose
release of insulin and glucagon is ___ in response to ___
cyclic
peaks and valleys of glucose concentrations
after eat, glucose conc goes up –> insulin’s conc immediately goes up to bring glucose back down thru absorption of it into liver
what is the downstream effect of the way insulin works?
has to do with how insulin receptor is controlled –> after insulin works, insulin receptor complex is engulfed and broken down to be recycled
cell surface receptor of target cell is then depleted, takes time to be restored –> if get another pulse of glucose during that critical time, going to get another pulse of insulin, but not normal amt of receptors, so receptors are less sensitive to insulin & wont respond –> insulin resistance –> type II diabetes
diabetes is associated with ___
early onset Alzheimers
what is the A1c test?
hemoglobin A1c, glucose sticks to hemoglobin in RBC (red cells have 3 month life span) –> can measure amt of glucose associated with hemoglobin in RBC, get a 3 month average of your blood glucose levels
