Glossary
exocytosis
Exocytosis is a vesicle fusing with the cell membrane and releasing its contents outside the cell — how a cell secretes what it makes.
Exocytosis is the reverse of taking something in: a vesicle inside the cell moves to the membrane, the two fuse, and the vesicle's contents are released outside. It is how a cell secretes what it makes — digestive enzymes from the pancreas, hormones from an endocrine cell, antibodies from a plasma cell — and how a nerve ending releases its neurotransmitter into the gap at a synapse. Two details carry the marks. The vesicle's membrane becomes part of the cell surface when it fuses, so a cell that secretes heavily has to take membrane back in to keep its size. And the process costs energy: a vesicle does not drift into the membrane by chance but is moved and anchored, and calcium entering the cell is the usual trigger. A question that asks how a large molecule leaves a cell is asking for this word, because large molecules cannot cross the bilayer any other way.
Taught in
Related terms
- phagocytosis — Phagocytosis is a cell taking in a solid particle by wrapping its membrane around it, then digesting it in a vesicle.
- ATP — ATP is the molecule cells use to carry energy — breaking off its third phosphate releases the energy a reaction needs.
Source: The biology guide in this course: its genetics definitions follow the National Human Genome Research Institute's Talking Glossary of Genomic and Genetic Terms, and its process descriptions follow the US National Cancer Institute's SEER Training Modules. Both are US federal government material, not subject to copyright in the United States. The microbiology entries — the bacterial cell, the Gram stain and the chain of infection — were written for this course from the infection-control guidance the biology guide's own source list names (US Centers for Disease Control and Prevention), which the genetics glossary does not cover. The definitions above are written for this course in our own words. (NHGRI Talking Glossary accessed 2026-10-26; definitions written 2026-10-27; the CDC basis for the microbiology entries — Principles of Epidemiology in Public Health Practice, third edition — accessed 2026-10-28, the date the biology guide's own source list records)