For a cell, one of the principal ways to absorb substances means functioning of clathrin-mediated endocytosis. This mechanism of absorption (internalization) comprises the development of a regular lining (coat) from special clathrin protein on the cytoplasmic surfaces of plasma membranes. The resulting clathrin pit concentrates receptors to various substances or ligands coming from the vascular lumen. That is why the mechanism is also called receptor-mediated endocytosis. Thanks to the process, the cells get their required substances, regulate the number of receptors, channels, and special membrane proteins; they also obtain antigens to process them; they also remove used and potentially harmful substances from the extracellular environment.

Fast assembling of the clathrin coat leads to the formation of a rounded structure called vesicle. The vesicle secedes from the plasma membrane and loses the clathrin coat soon, then entering a compartment of early endosomes. Clathrin-coated vesicles also participate in transfer of enzymes and membrane proteins from Golgi apparatus to lysosomes. For more details, see "Cell membranes of two endothelial cells"