Glucose Homeostasis Flashcards
For a healthy adult, the basal blood glucose is…
4-5mM
Why does the body regulate blood-glucose within a narrow range?
The body defends against low blood-glucose concentrations, hypoglycaemia
and high blood-glucose concentrations, hyperglycaemia
Beta-cells release…
Insulin to prevent hyperglycaemia
Alpha-cells release…
Glucagon to prevent hypoglycaemia
What mechanisms are responsible for maintaining such tight regulation of blood glucose?
While plasma glucose remains consistent, there is a robust increase in insulin concentrations with each meal.
Insulin acts to immediately lower blood glucose by promoting its up-take in cells.
Glucagon is constantly being degraded in the…
Post-absorptive state
Glucagon is maintained….
Between meals
*Important in preventing blood-glucose decline between meals
Glucose molecules are stored as…
Glycogen, readily available in the liver and muscles
When exercising, glycogen is catabolised to provide energy for contraction. T/F
True
Neurons can store glycogen. T/F
False.
Neurons cannot store glycogen
When glucose is limited, the brain switches to…
ketone-bodies; utilised for starvation
Exocrine cells:
- Arranged in lobules that secrete a range of digestive enzymes, sodium bicarbonate, and other electrolytes into the duodenum.
Endocrine cells:
Secrete hormones into systemic blood
Alpha cells:
release glucagon –> catabolic, mobilise glucose, fatty and amino acids for energy production
Beta cells:
releases insulin –> anabolic, storage of glucose, fatty, and amino acids
Gamma cells:
releases somatostatin –> local to the pancreas to inhibit insulin and glucagon secretion
The prime blood-glucose lowering hormone in the body is…
Insulin
Excess glucagon production causes a _____ , a tumour of the pancreatic alpha cells that hyper-secretes glucagon.
gucagonoma
C-peptide is secreted via…
Insulin and pancreatic beta-cells
C-peptide is biologically inactive as a metabolic hormone. T/F
True
A person with elevated blood glucose levels will likely exhibit increased secretion of _____ from their pancreatic beta-cells within the islet of Langerhans.
insulin
Insulin receptor substrates (IRS) are….
downstream and act as cytoplasmic protein scaffolds to organise signalling complexes
*IRS1 and IRS2 are ubiquitously expressed; primary mediators of insulin-dependant regulation of glucose metabolism. T/F
True
Glucose is hydro…
Hydrophillic
GLUT1 is found at:
- Blood
- Blood Brain Barrier
- Heart
**Insulin dependant
GLUT1-4 are insulin dependent. T/F
True
GLUT2 is found at:
- Liver
- Pancreas
- Small intestine
**Low affinity
GLUT3 is found at:
- Brain
- Neurons
- Sperm
**High affinity
GLUT4 is found at:
- Skeletal muscle
- Adipose tissue
- Heart
**Moderate affinity
GLUT5 is found at:
Enterocyte of interstitial epithilium (Luminal side)
GLUT5 is insulin INdependant and a transporter of…
Fructose
GLUTS are…
Sodium and ATP-dependant
Ubiquitous
SGLTs stand for:
Sodium-Glucose Transport Systems
SGLTs are…
Sodium dependant
Require ATP for a sodium gradient
SLGT1 is found at:
Enterocyte of interstitial epithelium
**Glucose absorption
SLGT2 is found at:
Proximal tubule of nephron in the kidney
MAPKpathway:
Promotes cell growth.
PI3K/PKBpathway:
Activated through IRS; promotes glucose transporters (GLUT4) translocation to cell surface.
PI3K/mTORpathway:
Activated through IRS; promotes protein synthesis, inhibits proteolysis, cell growth.
GLUT1→
Basal glucose uptake
Expressedinall tissue, Important in glucose crossing the blood brain barrier
GLUT2→
Importantin pancreatic beta cells and liver hepatocytes
GLUT3→
Basal glucose uptake, expressedinall tissue, important in CNS neurons
GLUT4→
Insulin stimulatedglucose uptake
Expressedinmuscle (skeletal and cardiac) and fat adipocytes
GLUT5→
Fructose transport in small intestine
Which of the following pathways are activated by insulin signal transduction?
MAPK: promotion of cell growth
P13K/MTOR: Promotion of protein synthesis, inhibits proteolysis and cell growth
P13K/PKB - promotion of movement of GLUT4 to the cell surface in muscle and adipose cells
How does the body ensure that insulin is secreted in response to digested nutrients.
The anatomical arrangement that allows nutrient rich blood from the GI-tract travels via the pancreas –> liver via the hepatic portal vein
How does insulin promote glucose uptake in the liver after a meal?
- Via expression and activation of enzymes that promotestorage and utilisation of glucose.
- Insulin maintains a concentration gradient in hepatocytes that favours glucose intake via GLUT2 (and other GLUTs) transporters (glucose movement is down the concentration gradient).
This occurs after a meal, when the blood glucose concentration is high.
Insulin binds to its receptor and activates the…
Tyrosine kinase domain
Insulin Receptor Substrates are phosphorylated by receptor kinases on tyrosine residues. T/F
True
Within hepatocytes, insulin…
PromotesGlycogenesis(storage of glycogen) and inhibitsGlycogenolysis (breakdown of glycogen to glucose)
