Pinocytosis is one of three forms of endocytosis, a cellular process that is used to take up smaller particles into a cell by splitting it into small particles. The particles then form small vesicles which subsiquently fuse with lysosomes to hydrolyze, or break down, the particles. This process requires adenosine triphosphate, the chemical compound used as energy in a majority of cells. Pinocytosis is primarily used for the absorption of extracellular fluids (ECF), and in contrast to phagocytosis generates very small vesicles. Unlike receptor-mediated endocytosis, pinocytosis is unspecific in the substances that it transports. The cell takes in surrounding fluids, including all solutes present.