Endocytosis and Exocytosis

Large molecules, such as proteins, enter (endocytosis) or exit (exocytosis) through the cell membrane by so-called vesicular transport. During this process, substances are attached in part to the outside of the cell by membrane-bound receptors, enclosed by a part of the plasma membrane, and moved into the interior of the cell as a membranewrapped vesicle (receptor-mediated endocytosis). Depending on the size of the absorbed particle, this process may also be called pinocytosis or phagocytosis.
In exocytosis, products synthesized in the cell are enclosed in membranous vesicles and, by coalescence of these vesicles with the inside of the plasma membrane, reach the extracellular space. In this way, the transmitter substances in the endings of nerve cell processes are liberated at the synapses. The secretory products of most glandular cells leave the cell interior in similar fashion. Endocytosis and exocytosis are dependent on the action of ATP.

Exocytosis and endocytosis