What does exocytosis mean?
Exocytosis is the process by which a cell exports materials from its interior to the outside environment. The cell packages the substance — which may be a protein, hormone, neurotransmitter, enzyme, or waste product — inside a small membrane-bound sac called a vesicle. This vesicle then travels to the cell's outer membrane, fuses with it, and opens, spilling its contents into the surrounding space. Exocytosis is fundamental to life: nerve cells rely on it to transmit signals between one another, glands use it to secrete hormones and digestive enzymes, and immune cells deploy it to release signalling molecules. Biologists distinguish regulated exocytosis, triggered by a specific signal such as a rise in calcium ions, from constitutive exocytosis, which proceeds continuously as part of routine cellular maintenance. The term derives from Greek roots meaning 'outside' and 'cell', and entered scientific vocabulary in the twentieth century as microscopy revealed the mechanics of membrane traffic. It is a purely technical term, encountered almost exclusively in biology and medicine.
nounA cellular process in which a cell transports material out of itself by enclosing it in vesicles that fuse with the cell membrane, releasing the contents to the exterior.
- The biological process by which cells release substances (such as proteins, neurotransmitters, or waste) via membrane-bound vesicles fusing with the plasma membrane.
"Neurotransmitters are released into the synapse through exocytosis."
"Insulin is secreted from pancreatic beta cells by regulated exocytosis."
"Under the electron microscope, the researchers observed vesicles undergoing exocytosis at the cell surface."
Rarely used; 'exocytosis' is usually treated as an uncountable noun referring to the process. The plural appears mainly in technical literature referring to multiple discrete events.
"Multiple exocytoses were recorded at the synaptic terminals during stimulation."
Every time you think, move, or feel anything, billions of tiny bubbles are fusing with your neurons' membranes — that's exocytosis doing the work.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of exocytosis
Exocytosis was coined in the twentieth century from the Greek elements 'exo-' (outside) and 'cytos' (cell), combined with the suffix '-osis' denoting a process or condition. It emerged as cell biologists came to understand how vesicles move materials across membranes. It shares its Greek roots with related terms such as endocytosis (its opposite) and pinocytosis, all describing forms of cellular transport.
Related word forms
How exocytosis is actually used
Strictly technical and scientific in register; used almost exclusively in biology, biochemistry, and medicine. Not used figuratively or informally. Plural 'exocytoses' exists but is rare; the word is typically treated as an uncountable mass noun referring to the process.
Easily confused with exocytosis
Endocytosis is the reverse process: the cell takes material in by engulfing it, whereas exocytosis expels material out of the cell.