Chylomicrons and Fat Transport

Chylomicron Basics

• Chylomicrons: Specialized protein carrier molecules
  • Packaged in the small intestine with hydrophobic molecules (e.g., fats, cholesterol)
  • Composed of a protein shell surrounding fat molecules

Chylomicron Formation and Transport

• Formation: In the small intestine
• Transport:
  • Enter lymphatic capillaries called lacteals
  • Drain into veins via the thoracic duct near the shoulder
  • Move through the heart to the lungs, then to arteries and capillary beds
  • Capillary beds are the site for fat absorption by tissues

Fat Absorption Process

• Capillaries: Positioned next to tissues for nutrient and oxygen uptake
• Enzymes in Capillary Beds: Lipoprotein lipase (LPL)
  • Activated by specific proteins on chylomicrons and insulin
  • Functions:
    • Breaks down triacylglycerides into individual fatty acids and glycerol
    • Notable: Brain and red blood cells can't take up fats

Fat Uptake by Tissues

• Muscle and Adipose Cells: Significant absorbers of fatty acids
  • Muscle: Uses fatty acids for ATP production
  • Adipose Cells: Store fats as triacylglycerides
    • Hormone-sensitive lipase: Releases fatty acids in response to hormone levels

Chylomicron Remnants and the Liver

• Remnants in Capillaries: Called chylomicron remnants (CR)
  • Contains leftover triglycerides and cholesterol
  • Reabsorbed by the liver

Liver's Role in Fat Processing

• VLDL Production: Packages remaining fats and newly formed fatty acids into VLDL (Very Low Density Lipoprotein)
  • Fate: Transported to capillary beds for fat and cholesterol release

Hormone Regulation of Fat Storage and Release

• Insulin and Glucagon: Regulate fat storage in adipose cells
  • Post-meal: High insulin levels stimulate fat storage
  • Fasting: Low insulin and high glucagon stimulate fat release

Fatty Acid Usage During Fasting

• Hormone-sensitive Lipase: Breaks down stored fats in adipose cells
  • Free fatty acids travel with albumin in the blood
  • Major consumers: Liver (gluconeogenesis) and other tissues except the brain and RBCs