Category: cellular biology Category: fabric The tight junctions (or tight junctions , tight junctions or zonula occludens ) are specific epithelial fabrics of the Taxon of the Chordé S. They completely block the circulation of fluids between the cell S and thus ensure the sealing between two compartments fabric laires.

Structure

The tight junctions are localized with the apex of the cells epithelial S where they form a band continues around which ensures the sealing. With the Microscope, when one separates both membrane S cellular, one observes a series of pads longilignes, more or less inter-connected but ever stopped. The two membranes comprise exactly the same network of pads. These pads are complementary to visible furrows on the inner face of the plasmic Membrane. The significance of this structure was not included/understood of continuation; it was initially identified as of the linear proteins which ensure the sealing. It of it is nothing. So Protéine S take part in the regulation and the stability of the structure, like the CAMWOOD cadhérines or the CAMWOOD of the superfamille of Immunoglobilines, they do not constitute the heart of it. In fact, it is about a fusion partial of the plasmic membranes: on the level of the junctions, the extracytoplasmic hémimembranes disappear and both hémimembranes cytoplasmic join to reconstitute a membrane, supplements, but made up of elements coming as of those cells. On the level of the polarized epitheliums intervene of proteins with 4 transmembrane fields and extracellular field court: claudines and occludines. These proteins allow the bringing together of the two plasmic membranes

Functions

The principal function is to ensure the sealing of the epitheliums, such as that which separates the interior and the outside of the Intestin, or to prevent that the organization does not empty itself of its water by the multiple epitheliums in contact with the external medium such as the skin, the tract digestive, even the germinatif epithelium. On the other hand, the epitheliums which must easily be crossed, like the vascular Endothélium, are completely deprived by it, except for some exceptions. Most known is that of the blood-vessels which irrigate the brain, where the very many tightened junctions are at the origin of the hematoencephalic Barrière, obliging all the Molécule S which want to penetrate there (and a fortiori the pathogenic Microorganisme S, much larger) to cross the cells endothéliales.

Their role is not limited to a sealing off between compartments. They mark also the border between two zones of the plasmic membrane of the cells epithelial, the apical membrane and the basal membrane, functionally very different. The presence of this junction blocks specific proteins of each zone and prevents them from reaching the other zone. The tight junctions are responsible for the maintenance of the Polarité of the cells endothéliales.

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