Cholesterol metabolism

Cholesterol and its esters are either:

• ingested and absorbed from the diet in chylomicrons and then conveyed to:
  • peripheral cells for:
    • membrane synthesis
    • steroid production e.g. the adrenal cortex
    • if excess cholesterol is present, re-esterification of cholesterol via the enzyme acyl-CoA-cholesterol acyl transferase; this permits storage
  • hepatocytes for:
  • biliary excretion
    • conversion into bile salts
    • packaging into VLDL or pre-HDL molecules
      
      
• synthesised de novo in hepatocytes before direction into similar fates e.g. biliary excretion

Cholesterol and its esters are transported haematogenously in a range of lipid-carrying particles; the most important are LDL and HDL. LDL is taken up by endocytosis by peripheral cells after recognition through cell surface LDL receptors.

The plasma cholesterol concentration is decreased by thyroid hormones which increase LDL receptors, and by oestrogens which increase hepatic catabolism of LDL.