Types and functions

• WAT
  • structure:
    • honeycomb structure
    • almost completely filled with one lipid droplet, nucleus pushed to the side
  • function
    • energy storage
    • insulation
    • steroid metabolism (mostly postmenopausal)
    • adipokines production (cytokine-like molecules) e.g. leptine
• BAT
  • stucture:
    • smaller, more lipid droplets
    • many mitochondria
  • function:
    • burning (excess) energy
    • body temperature
    • hibernation

white fat cells:

• take up:
  • free fatty acids breakdown outside the cells
  • back into TGs into the cells for storage
  • Glycerol can be taken up directly (AQ7) or as glucose (GLUT4), both are converted into glycerol-3-P
• store
  • lipid droplet is covered by proteins
• release (lipolysis):
  • for release the TGs are broken down again

Regulation by insulin:

Adipocytes have an insulin receptor.

causes uptake of glucose and inhibition of ligases:

• Glut4 is moved to the membrane because of activation of AKT2
• AKT2 also inhibits ligases and therefore FFA release.

Insulin action:

• muscle
  • glucose uptake increases
  • glycogenesis increases
  • 90% of glucose storage
• AT
  • glucose uptake increases
  • lypolysis increases
  • 10% of glucose storage
• liver
  • gluconeogenesis decreases
  • glycogenolysis decreases
  • glycogenesis increases

Muscle in detail:

• GLUT4 also transported to the membrane upon insulin binding (again through AKT2).
• AKT2 also inhibits glycogensynthase kinase → less inhibition of GS = more glycogen production