Britannica Sources used in this answer

How do LDL and HDL transport cholesterol in different directions?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

A composite diagram shows the structural formulas, space-filling models, and simplified depictions of lipid molecules including stearic acid and phosphatidylcholine, and how these assemble into a micelle and lipid bilayer, with labels identifying hydrophilic heads and hydrophobic tails. — Lipid Structure and properties of two representative lipids. Both stearic acid (a fatty acid) and phosphatidylcholine (a phospholipid) are composed of chemical groups that form polar “heads” and nonpolar “tails.” The polar heads are hydrophilic, or soluble in water, whereas the nonpolar tails are hydrophobic, or insoluble in water. Lipid molecules of this composition spontaneously form aggregate structures such as micelles and lipid bilayers, with their hydrophilic ends oriented toward the watery medium and their hydrophobic ends shielded from the water.

Low-density lipoproteins (LDL) and high-density lipoproteins (HDL) serve distinct roles in the transport of cholesterol throughout the body to maintain lipid homeostasis.

LDL (Low-Density Lipoprotein): LDL acts as the primary carrier that transports cholesterol from the liver—where it is synthesized—to the peripheral tissues and organs of the body. Once it reaches a target cell, the LDL particle binds to specific receptors on the cell surface and is internalized via endocytosis, allowing the cell to utilize the cholesterol for biological membranes or storage.123
HDL (High-Density Lipoprotein): HDL functions in the opposite direction. It collects excess or unused cholesterol from the body's peripheral tissues and transports it back to the liver. Once returned to the liver, this cholesterol is metabolized into bile acids and salts for ultimate excretion from the body.132

Because of these opposing pathways, LDL is often associated with the accumulation of fatty deposits in blood vessels, while HDL is considered beneficial for its role in removing excess cholesterol from circulation.3