U1ii: Describe the role of insulin in fat metabolism

Insulin Summary

  • Polypeptide Hormone
  • Stored + synthesised by β cells of pancreas
  • Ca2+ required for exocytosis & release
  • Released when BSL > 6mmol/L
  • Binds Insulin Receptor A subunits
  • Activates TK
  • Autophosphorylation of receptor
  • Alters intracellular gene transcription
  • Major ANABOLIC HORMONE

Fat Metabolism

Adipose Tissue

    • ↑fat synthesis
    • ↑glucose uptake via GLUT-4
    • Glycolysis: glucose → Acetyl CoA
    • One Acetyl CoA has 2-C → add additional Acetyl CoA until you have FA of appropriate length → storage as TAGs

↑ Fat Absorption

    • LIPOPROTEIN LIPASE (LPL) is synthesised by skeletal m. + AT
    • ↑[Insulin] post meal → ↑AT LPL secretion
    • LPL hydrolyses TAGs → release Glycerol + FAs

→ Taken up by tissues for E. oxidation / re-esterification & storage

↓ Fat Breakdown

    • Inhibits HORMONE SENSITIVE LIPASE (HSL)
    • HSL breaks stored TAGs → glycerol + FFA → circulation
    • Inhibits ketogenesis

Liver

↑ Fat Synthesis

    • ↑glucose entry via GLUT-4 (but not required v. perm to CHO)
    • Glucose converted to glycogen
    • When glycogen stores maximal (100g), excess glucose → pyruvate → Acetyl CoA → stored TAGs

↓ Fat Breakdown

    • Inhibits gluconeogenesis
    • Inhibits ketoneogenesis

Skeletal Muscle

  • ↑LIPOPROTEIN LIPASE secretion → breaks down digested fat to release TAGs → Glycerol + FA for storage
  • ↓Ketogenesis