The exocytose (of the Greek - exo " except de" and of - kutos " cavity, cellule") is the mechanism by which the cell releases broad Biomolécules through its membrane. The exocytose takes place when blisters of transport or secretion amalgamate with the plasmic membrane and leave in the extracellular medium. Example: expulsion of neurotransmitters of the synaptic blisters about the extracellular middle.

Whereas at the Protozoa (unicellular organizations), the exocytose has a function of waste disposal, in the multicellular organizations, it has also a role for the functions of indication and regulation.

Types of exocytose

In the multicellular organizations, there are two types of exocytose:

1) Started by Ca²⁺= exocytose controlled

2) Constitutive

The exocytose started by Ca²⁺ occurs in the Synapse S and is used for indication interneuronale.

The constitutive exocytose is carried out by all the cells and allows the release of components of the extracellular matrix or simply the delivery of membrane Protéines lately synthesized which will be built-in the cellular membrane at the time of the fusion of the Vésicule of transport.

Example: acetylcholine

• the acetylcholine intervenes in the muscular contraction at the time of the reflexes of inflection or extension to the level of the junction neuromusculaire. The neurons producing it are called cholinergic neurons.

• Its precursors are the food choline of origin which is collected by the presynaptic termination in blood and the acétylcoenzyme has origin mitochondriale. They are synthesized by the enzyme choline-acétyltransférase (CAT) which transforms them into acetylcholine. These neurotransmitters are then wrapped by blisters coming from the budding of the Appareil of Golgi and are transported to the bulge (or button) synaptic. At the presynaptic level there is not only one bulge but hundreds in order to ensure a broader surface of contact; one speaks about final arborisation.
• Under the effect of calcium the blisters are then pushed until amalgamating with the plasmic membrane. This discharge of neurotransmitter molecules in the synaptic slit is called the exocytose. It is said that the synapse is cholinergic.
• the neurotransmitters are fixed then on specific receivers of the driving plate of the striated muscle what results in to contract it. The neurotransmitter excess is then degraded by a Enzyme: acetylcholine-estérase (AITCH) which releases from the acetic acid and of choline which could be then recaptured by the receivers of the presynaptic axon.

See too

• Endocytose
• synaptic Neuro-transmitter
• Transmission

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