Nutrient Metabolism: Insulin and Glucagon Flashcards
Glucose-dependent tissues?
brain, neurons, RBCs, intestinal mucosa, renal medulla
in glucose-dependent tissues:
conc gradient drives glucose entry
- glucose transporters are always in plasma membrane
- insulin-independent glucose transport
glucose-independent tissues?
skeletal muscle, fat, liver
in glucose-independent tissues:
glucose transport is regulated by insulin
glucose transporters are NOT always in plasma membrane
Absorptive Phase:
eating and digesting meal and absorbing nutrients
- 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
Fasting Phase:
at least 8 hours with no nutrient intake
- breakdown of glycogen and triglycerides
- maintain plasma glucose between** 70-100 mg/mL**
- minimize glucose uptake
- gluconeogenesis in liver
insulin
beta cells of pancreatic islets
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
GLP-1
incretin hormone
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
stimuli that decreases insulin secretion
EPI and NE
insulin metabolism
- half removed during 1st pass
- C-peptide is not removed so used as indicator of pancreatic function and initial insulin secretion
Glucagon
alpha cell of pancreatic islets
dominant during fasting phase
- threshold for glucagon secretion, plasma glucose = 65-70 mg/dL
stimuli that increases glucagon secretion
- low glucose and high AA
- NE and EPI
- stressors
- increased cortisol
stimuli that decrease glucagon secretion
- increase glucose and decrease AA
- increase islet insulin secretion
high insulin:glucagon ratio
absorptive phase
promote storage of excess nutrients
inhibit breakdown of endogenous storage depots
low insulin:glucagon ratio
fasting phase
stimulate breakdown of endogenous storage depots
maintain adequate plasma glucose and fatty acids
with short-term fasting, as insulin decreases
(interdigestive period)
glycogen stores are first used
counter-regulatory hormones protect against hypoglycemia
glucagon
epinephrine
cortisol
growth hormone
EPI controls during exercise, stress, hypoglycemia
if hypoglycemia severe and persists for several hours, cortisol and GH help
adipokines
TNF alpha and IL-6
insulin sensitivity of skeletal muscle and glucose sensitivity of pancreatic beta cells
adiponectin
beta cell proliferation
pathology of obestity
- increased secretion of leptin and adipokines
- decreased secreion of adiponectin
T1DM
destruction of pancreatic beta cells
hyperglycemia due to very low or absent insulin secretion
- diabetic ketoacidosis
