Exocytosis functions in secretion of substances from cells to the extracellular matrix or transport of membrane components to the plasma membrane. All cells require the use of the constitutive form of exocytosis which helps in building and maintaining plasma membrane and/or cell wall integrity. On the other hand specialized cells which secrete proteins and other components into the extracellular matrix (eg. hormones secreted by pancreatic cells) use regulated exocytosis. The products to be secreted are assembled in vesicles at the Golgi membranes in both types of exocytosis. The substances secreted by regulated exocytosis, are concentrated in vesicles near the plasma membrane. They fuse with the plasma membrane only when an external signal triggers the fusion resulting in a rapid secretion of the vesicular contents. So regulated exocytosis would be activated only when there is a need for a hormone or enzyme to be secreted by a cell type while constitutive exocytosis happens continously.
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