Cholesterol: Essential Component and Risk Factor

Importance of Cholesterol

• Role in Animal Cells:
  • Integral part of the cell membrane.
  • Provides membrane fluidity.
  • Participates in cellular processes.
  • Precursor for:
    • Bile
    • Steroid hormones
    • Vitamin D

Cholesterol Sources

• Obtained through dietary intake.
• Endogenous synthesis by cells.
• Regulation:
  • Negative feedback control.
  • Low intracellular cholesterol stimulates production.
  • High cholesterol levels inhibit production.

Lipoproteins: Cholesterol Transporters

• Structure: Assembly of lipids and proteins.
• Classification by Density:
  • Lipids are lighter than proteins, affecting size and density.
• Types and Functions:
  • Low-Density Lipoprotein (LDL):
    • Carries cholesterol from the liver to tissues.
    • Known as "bad cholesterol."
  • High-Density Lipoprotein (HDL):
    • Returns excess cholesterol to the liver.
    • Known as "good cholesterol."

Metabolism of Cholesterol

• Dietary Cholesterol:
  • Absorbed in the intestine.
  • Transported to the liver via blood.
• Liver's Role:
  • Packages cholesterol into Very Low-Density Lipoprotein (VLDL).
  • VLDL travels to organs, becoming LDL after triglyceride extraction.
• Peripheral Cells:
  • Uptake LDL via endocytosis.
  • Use cholesterol for membranes and other functions.
  • Excess cholesterol exported via HDL for reverse transport.
• Bile Production:
  • Liver uses cholesterol to produce bile.
  • Bile aids in fat breakdown in the intestine.
  • Part of bile excreted, part recycled to the liver.

Health Implications

• LDL:
  • High levels lead to cholesterol plaque buildup.
  • Associated with cardiovascular diseases (heart attacks, strokes).
• HDL:
  • Removes excess cholesterol.

Cholesterol-Lowering Drugs

• Types:
  • Inhibitors of endogenous cholesterol production.
  • Inhibitors of intestinal cholesterol absorption.
  • Inhibitors of bile reuptake.