Cytosis

Cytosis is a transport mechanism for the movement of large quantities of molecules into and out of cells.

There are three main types of cytosis: endocytosis (into the cell), exocytosis (out of the cell), and transcytosis (through the cell, in and out).

The word cytosis (/saɪˈtoʊsᵻs/) uses combining forms of and , reflecting a cellular process. The term was coined by Novikoff in 1961.

Endocytosis is when a cell absorbs molecules, such as proteins, from outside the cell by engulfing it with the cell membrane. It is used by most cells, because many critical substances are large polar molecules that cannot pass through the cell membrane. The two major types of endocytosis are pinocytosis and phagocytosis.

Exocytosis is when a cell directs the contents of secretory vesicles out of the cell membrane. The vesicles fuse with the cell membrane and their content, usually protein, is released out of the cell. There are two types of exocytosis: Constitutive secretion and Regulated secretion. In both of these types, a vesicle buds from the Golgi Apparatus and are shuttled to the plasma membrane to be exocytosed from the cell. Exocytosis of lysosomes commonly serves to repair damaged areas of the plasma membrane by replenishing the lipid bi-layer.

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