Exocytosis

Exocytosis is the reverse of endocytosis.

And that is just as well. In 30 minutes an active cell like a macrophage (right) can endocytose an amount of plasma membrane equal to its complete plasma membrane.

This electron micrograph (courtesy of Dr. Robert J. North) shows a guinea phagocyte ingesting polystyrene beads. Several beads are already enclosed in vacuoles while the others are in the process of being engulfed.

So the cell must have a mechanism to restore the normal amount of plasma membrane. Exocytosis is that mechanism.

The process.

Membrane-bound vesicles move to the cell surface where they fuse with the plasma membrane. This accomplishes three things:

Exocytic vesicles are created from several sources:

Some cells specialize in secretion. In cells that secrete large amounts of protein, for example, the protein accumulates in specialized secretory granules formed by the Golgi apparatus. These move to the cell surface and discharge their contents to the outside.

Examples:

(* originally published in Fawcett, The Cell: Its Organelles and Inclusions, W. B. Saunders Co., 1966.)

Welcome&Next Search

30 May 1999