Cholesterol synthesized in the liver is transported to peripheral cells via low-density lipiproteins (LDLs) (Figure 18.7). LDLs are taken up by the cells in the process called receptor-mediated endocytosis. This process involves binding of the LDL to the LDL receptors, located in coated pits, followed by engulfment of the LDL. Several of these engulfed vesicles come together in the cell to form an endosome (Figure 18.10), which fuses with a lysosome to digest the contents.

Receptor-mediated endocytosis is now known to be a widely used pathway for internalization of extracellular substances, including other lipoproteins, cell growth factors, and some viruses.