Gynthesis of glycogen from glucose
What are the four factors insulin exerts on carbohydrates?
(1) Facilitates glucose transport into most cells
(2) Stimulates glycogenesis
(3) Inhibits glycogenolysis
(4) Decreases hepatic output by inhibiting gluconeogenesis.
What is the plasma membrane carrier transports glucose between the blood and cells?
GLUT (glucose transporter)
What happens to glucose immediately upon entering the cell?
physphorylation into glucose-6-phosphate
Purpose of GLUT-1
Transport glucose across blood-brain barrier
Purpose of GLUT-2
Transfers into the adjeacent bloodstream the glucose that has entered the kidney and intestinal cells by means of sodium and glucose cotransporter (SGLT)
Purpose of GLUT-3
Main transporter of glucose into neurons
Purpose of GLUT-4
Majority of glucose uptake by most cells
What hormone allows for GLUT-4 action?
Insulin binding is required for GLUT-4 action
T/F all GLUT carriers respond to insulin
False (GLUT-4 only)
T/F GLUT-4 is always present on the plasma memebrane
False (absent w/o insulin)
How does insulin promote GLUT-4 expression?
Insulin binds its receptor which signals intracellular vesicles containing GLUT-4 to bind with cell membrane, inserting the GLUT-4
T/F GLUT-4 is degraded after glucose transport
False (recycled via endocytosis)
T/F The brain, working muscles, and the liver are not insulin dependent for glucose update
T/F Glucose permeability to the brain via GLUT-1, GLUT-3, GLUT-4
False (GLUT-1, GLUT-3)
T/F Skeletals muscles always require insulin for glucose uptake
False (Only at rest, not during exercise)
T/F Insulin stimulates insertion of GLUT-4 in skeletal muscles during exercise
False (muscle contractions trigger insertion of GLUT-4)
T/F The liver does not require GLUT-4
T/F Insulin enhances glucose metabolism in the liver
What are the four effects of insulin on fat?
(1) Enhances entry of fatty acids into adipose tissue
(2) Increases transport of blusoe into adipose tissue (GLUT-4 recruitment)
(3) Promotes triglyceride synthesis (indirectly)
(4) Inhibits lipolysis
What are the three actions of insulin on protein?
(1) Promostes active transport of aa from blood into muscles and other tissue
(2) Increases rate of aa incorporation into protein
(3) Inhibits protein degradation
T/F Insulin is essential for normal growth
True (glucose -> anabolic effect on protein)
What is the primary stimulus for increased insulin secrtion?
Increase in blood glucose concentration
Via what mechanism does glucose stiulate insulin secretion?
excitation-secretion coupling process: changes B cell's membrane potential->insulin secretion
Glucose stimulation of insulin: Step 1
Glucose enteres B cell via GLUT-2
Glucose stimulation of insulin: Step 2
Glucose phosphorylated to glucose-6-phosphate
Glucose stimulation of insulin: Step 3
Glucose-6-phosphate oxidized by to yield ATP
Glucose stimulation of insulin: Step 4
ATP closes ATP-sensitive K+ channel on binding
Glucose stimulation of insulin: Step 5
Decrease K+ permeability leads to depolarization of B cell
Glucose stimulation of insulin: Step 6
Depolarization cause volatage-gated Ca++ channels to open
Glucose stimulation of insulin: Step 7
Ca++ enters cell through open channels
Glucose stimulation of insulin: Step 8
Ca++ entry triggers exocytosis of secretory vesicles containing insulin
Glucose stimulation of insulin: Step 9
Insulin is secreted
How does aa level affect insulin release?
Elevated aa levesl directly simulates the B cells to increase insulin secretion. ++Insulin enhances the entry of these aa into the cell, lowering blood aa levels and promoting protein synthesis
What mechanism causes aa to simtulate insulin release?
Same pathway as glucose: aa oxidation -> ATP production and start of cascade
What are incretins?
They increase insulin secrtion by increasing cAMP, enhancing Ca++ induced relesae of insulin
What are the two incretins?
GIP (glucose-dependent insulinotropic peptide), GLP (glucagon-like peptide)
T/F The gastrointestinal incretins work via negative feedback to regulate insulin
False (feedforward: anticipatory release prior to actual nutrient absorption)
T/F Parasympathetic activity inhibits insulin release
T/F Sympathetic stimulation increases epinephrine and inhibits insulin secretion
Why would sympathetic stimulation inhibit insulin secretion?
Decreased insulin increases blood glucose concentration availablity for fight/flight response or increased muscle activity
What is the most common endocrine disorder?
What is the most prominent feature of diabetes mellitus?
What is the key characteristic of both diabetes mellitus and diabetes insipidus?
polyuria (large urine volume)
Key character of DM Type I
lack of insulin secretion
Key character of DM Type II
insulin resistance (normal (or increased) insulin secretion but reduced sensitivity)
What are the two gross contributors of death due to insulin deficiency?
(1) effects of hyperglycemia
(2) ketosis toxicity (acidosis)
Why does hyperglycemia lead to death?
Hyperglycemia -> polyuria -> dehydration -> (1) CNS failure (2) Low peripheral cirulation (a) low cerebral flow (b) renal failure -> death