hormonal regulation of metabolism

Question 1

effect of pancreatic insulinoma

Answer 1

increases insulin production, leads to fasting hypoglycemia

Question 2

action of insulin

Answer 2

stimulates glucose uptake into tissues for use and storage

Question 3

steps of insulin synthesis

Answer 3

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

Question 4

describe the biphasic release of insulin

Answer 4

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

Question 5

typical insulin level at fasting blood glucose

Answer 5

usually 1

Question 6

to what blood glucose level can insulin accommodate

Answer 6

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

Question 7

stimulatory effects of insulin (5)

Answer 7

uptake of glucose into (some) tissues
use of glucose
fat synthesis
fat storage
general protein synthesis

Question 8

inhibitor effects of insulin (2)

Answer 8

glycogen breakdown

fat mobilization

Question 9

major glucose transporter in muscle and adipocytes

Answer 9

GLUT-4

Question 10

effect of insulin on the liver

Answer 10

stimulates use of glucose (like glycogen synthesis and glycolysis), but does NOT direct glucose uptake

Question 11

what is the action of glucokinase in the liver?

Answer 11

insulin stimulates glucokinase in the liver, action of glucose kinase is to phosphorylate glucose to effectively trap it in the liver

Question 12

which type of cells discussed use insulin-indpendent methods of glucose uptake?

Answer 12

neural cells

Question 13

normal vs. abnormal response to glucose tolerance test

Answer 13

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

Question 14

glycemic index

Answer 14

area under 2 hr glucose curve after feeding a 50 g test CHO portion

Question 15

what is the “standard for GI”?

Answer 15

white bread, GI = 1.0

Question 16

ways to increase GI

Answer 16

refine, make more simple sugars

Question 17

ways to decrease GI

Answer 17

add fiber, fat, protein

Question 18

glucagon source and structure

Answer 18

pancreatic a-cells
proglucagon = 160 aa
mature form = 29 aa
short half life in plasma

Question 19

what will stimulate glucagon secretion? (4)

Answer 19

• low blood glucose
• epinephrine
• cortisol
• exhaustive exercise

Question 20

what inhibits glucagon secretion? (2)

Answer 20

high insulin

high glucose

Question 21

what does glucagon act on directly?

Answer 21

liver and adipocytes

Question 22

what can glucagon not act on directly?

Answer 22

muscle, bc it lacks glucagon receptors

Question 23

what does glucagon stimulate? (3)

Answer 23

• glycogenolysis in liver
• breakdown of TAG in adipocytes to fatty acids and glycerol
• breakdown of protein in muscle to provide aa for gluconeogenesis

Question 24

what does glucagon inhibit? (2)

Answer 24

glycogen synthesis

fat storage

Question 25

what hormone stimulates glycogen mobilization in muscle?

Answer 25

epinephrine

Question 26

what is the result of glucogenolysis in muscle?

Answer 26

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

Question 27

which tissues are acted on by epinephrine?

Answer 27

liver, adipocytes, muscle

Question 28

what is the effect of epinephrine on glucagon? insulin?

Answer 28

glucagon- stimulates release

insulin- inhibits release

Question 29

which tissue lacks glucagon receptors?

Answer 29

muscle

Question 30

which tissues are acted on by glucagon?

Answer 30

liver, adipocytes

Question 31

what signaling pathway is common for epinephrine and glucagon?

Answer 31

both use GaS, increase cAMP and activate protein kinase a

Question 32

what is activated by protein kinase A?

what is inactivated by protein kinase A?

Answer 32

activated- glycogen phosphorylase, lipase

inactivated- glycogen synthase, fatty acid synthesis

Question 33

how does cortisol stimulate fuel mobilization?

Answer 33

binds to intracellular receptors and regulates gene transcription

Question 34

what is unique about the action of cortisol?

Answer 34

it is released in times of stress, but it stimulates glycogen synthesis NOT breakdown

Question 35

insulin vs protein kinase a

Answer 35

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

Question 36

describe hormone changes after protein only meal

Answer 36

• 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

Question 37

in “mixed” meals, which 2 aa in particular, will stimulate insulin release in response to glucose?

Answer 37

lysine

arginine