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Exocytosis (/ ˌ ɛ k s oʊ s aɪ ˈ t oʊ s ɪ s / [1] [2]) is a form of active transport and bulk transport in which a cell transports molecules (e.g., neurotransmitters and proteins) out of the cell (exo-+ cytosis). As an active transport mechanism, exocytosis requires the use of energy to transport material.
For example: proteins, enzymes or toxins (such as cholera toxin in pathogenic bacteria e.g. Vibrio cholerae) from across the interior (cytoplasm or cytosol) of a bacterial cell to its exterior. Secretion is a very important mechanism in bacterial functioning and operation in their natural surrounding environment for adaptation and survival.
Active transport enables these cells to take up salts from this dilute solution against the direction of the concentration gradient. For example, chloride (Cl −) and nitrate (NO 3 −) ions exist in the cytosol of plant cells, and need to be transported into the vacuole. While the vacuole has channels for these ions, transportation of them is ...
Merocrine – the cells of the gland excrete their substances by exocytosis into a duct; for example, pancreatic acinar cells, eccrine sweat glands [dubious – discuss], salivary glands, goblet cells, intestinal glands, tear glands, etc. Apocrine – the apical portion of the cytoplasm in the cell membrane, which contains the excretion, buds off.
Merocrine secretion Paneth cells, located at the base of the crypts of the small intestinal mucosa, and displaying merocrine secretion of bright red cytoplasmic granules. H&E stain. Merocrine (or eccrine) is a term used to classify exocrine glands and their secretions in the study of histology.
It is an example of fluid phase endocytosis and is usually a continuous process within the cell. The particles are absorbed through the use of clathrin -coated pits. These clathrin-coated pits are short lived and serve only to form a vesicle for transfer of particles to the lysosome.
For example, in the fertilized sea urchin egg, it has been shown that the cortical granule exocytosis immediately follows the calcium increase after approximately 6 seconds. In mammals, the first calcium wave occurs within 1–4 minutes following fertilization, and cortical granule exocytosis occurs within 5–30 minutes following fertilization.
Some vesicles don't fuse immediately and await a signal before starting the fusing. This is seen in vesicles carrying neurotransmitter in presynaptic cells. This process constitutes an effective cell-cell signaling mechanism via membrane vesicle trafficking from secretory cell to the target cells in human or animal body.