Endocytosis

Endocytosis is the uptake of extracellular macromolecules   across the plasma membrane into the cell. The objects to be ingested is progressively  enclosed through a  small  portion  of  the  plasma  membrane that  first  invaginates   and  then pinches off to form an intracellular  vesicle containing  the ingested  macromolecule. Endocytosis  can be separated into three distinct kinds depending  on the size of the ingested  macromolecule  and whether  specific  cell surface  receptors  are included. These three procedures are receptormediated endocytosis pinocytosis, and phagocytosis.