Nutrient Metabolism: Insulin and Glucagon

Question 1

Glucose-dependent tissues?

Answer 1

brain, neurons, RBCs, intestinal mucosa, renal medulla

Question 2

in glucose-dependent tissues:

Answer 2

conc gradient drives glucose entry
- glucose transporters are always in plasma membrane
- insulin-independent glucose transport

Question 3

glucose-independent tissues?

Answer 3

skeletal muscle, fat, liver

Question 4

in glucose-independent tissues:

Answer 4

glucose transport is regulated by insulin
glucose transporters are NOT always in plasma membrane

Question 5

Absorptive Phase:

eating and digesting meal and absorbing nutrients

Answer 5

• elevation of plasma glucose, AA, and fatty acids
• maximize glucose uptake
• store excess substrate
• inhibit endogenous substrate degradation
• after meal, plasma glucose <180 mg/mL

Question 6

Fasting Phase:

at least 8 hours with no nutrient intake

Answer 6

• breakdown of glycogen and triglycerides
• maintain plasma glucose between** 70-100 mg/mL**
• minimize glucose uptake
• gluconeogenesis in liver

Question 7

insulin

beta cells of pancreatic islets

Answer 7

dominant during absorptive phase
- threshold for insulin secretion = plasma glucose of 80 mg/mL
- high plasma glucose, AA and fatty acids increase insulin secretion
- ACh and incretin hormones also increase insulin secretion

Question 8

GLP-1

incretin hormone

Answer 8

increases insulin secretion during absorptive phase
- converted to GLP-1 fragment (inactive) by dipeptidyl peptidase IV
- antagonists of DPP IV to slow GLP-1 breakdown so increase insulin secretion

Question 9

stimuli that decreases insulin secretion

Answer 9

EPI and NE

Question 10

insulin metabolism

Answer 10

• half removed during 1st pass
• C-peptide is not removed so used as indicator of pancreatic function and initial insulin secretion

Question 11

Glucagon

alpha cell of pancreatic islets

Answer 11

dominant during fasting phase
- threshold for glucagon secretion, plasma glucose = 65-70 mg/dL

Question 12

stimuli that increases glucagon secretion

Answer 12

• low glucose and high AA
• NE and EPI
• stressors
• increased cortisol

Question 13

stimuli that decrease glucagon secretion

Answer 13

• increase glucose and decrease AA
• increase islet insulin secretion

Question 14

high insulin:glucagon ratio

absorptive phase

Answer 14

promote storage of excess nutrients
inhibit breakdown of endogenous storage depots

Question 15

low insulin:glucagon ratio

fasting phase

Answer 15

stimulate breakdown of endogenous storage depots
maintain adequate plasma glucose and fatty acids

Question 16

with short-term fasting, as insulin decreases

(interdigestive period)

Answer 16

glycogen stores are first used

Question 17

counter-regulatory hormones protect against hypoglycemia

Answer 17

glucagon
epinephrine
cortisol
growth hormone

EPI controls during exercise, stress, hypoglycemia

if hypoglycemia severe and persists for several hours, cortisol and GH help

Question 18

adipokines

TNF alpha and IL-6

Answer 18

insulin sensitivity of skeletal muscle and glucose sensitivity of pancreatic beta cells

Question 19

adiponectin

Answer 19

beta cell proliferation

Question 20

pathology of obestity

Answer 20

• increased secretion of leptin and adipokines
• decreased secreion of adiponectin

Question 21

T1DM

destruction of pancreatic beta cells

Answer 21

hyperglycemia due to very low or absent insulin secretion
- diabetic ketoacidosis