The ability to internalize material from outside the cell is important for several cellular processes including the ingestion of essential nutrients, removal of dead or damaged cells from the body, and defense against microorganisms. <span>Eukaryotic cells </span>internalize fluid, large and small molecules, and even other cells from their surroundings by a process called endocytos<span>There are two main types of endocytosis that are distinguished by the size of the vesicle formed and the cellular machinery involved. Pinocytosis (cell drinking) describes the </span>internalization<span> of extracellular fluid and small </span><span>macromolecules </span><span>by means of small vesicles. </span><span>Phagocytosis </span>(cell eating) describes the ingestion of large particles such as cell debris and whole microorganisms by means of large vesicles. While all eukaryotic cells are continually ingesting fluid and molecules by pinocytosis, only specialized phagocytic cells ingest large particles.<span> </span>is. During endocytosis, the plasma membrane of the cell forms a pocket around the material to be internalized. The pocket closes and then separates from the inside surface of the plasma membrane to form a membrane-enclosed bubble, or vesicle, containing the ingested material.
