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Mechanism whereby material found within endomembrane vesicles (secretory vesicles) are secreted (or excreted) out of eukaryotic cells.
Exocytosis involves the fusion of a secretory vesicle with the plasma membrane of a cell. The result is conversion of the contents of the lumen of the vesicle into material that instead is found outside of the cell.
All sorts of materials exit cells in this manner, most notably secreted proteins and various non-protein signaling molecules (such as neurotransmitters) as well as waste materials found within the endomembrane system (such as following digestion of the material located within a phagolysosome).
Just as endocytosis does not involve movement of materials that are found outside of a cell directly into the cytoplasm/cytosol of a cell, exocytosis does not involve movement of materials that are directly found within the cytoplasm/cytosol to outside of the cell. Instead, this is another indication of how the lumen of the endomembrane system and the extracellular environment to a certain degree are interchangeable.
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