During exocytosis, material from a cell is released. First a cell gathers and packages a certain particle (this package is called a vesicle). Because the vesicle is composed of the same material that makes up the cell membrane, when it reaches the membrane, the two structures merge together much like air bubbles do in liquid. The contents of the vesicle are then expelled from the cell. For example, cells that manufacture specific proteins, such as the pancreatic cells that manufacture insulin, use the process of exocytosis to secrete insulin into the blood.