A<unk>  is a structure within a tissue of a multicellular organism.<unk> s are especially abundant in epithelial tissues. They consist of protein complexes and provide contact between neighbouring cells, between a cell and the extracellular matrix, or they build up the paracellular barrier of epithelia and control the paracellular transport.
File:Cell junction simplified.svg
In vertebrates, there are three major types of<unk> s:
Adherens junctions and Desmosomes
Gap junctions
Tight junctions
Invertebrates have several other types of specific junctions, for example Septate junctions or the CeAJ (C. elegans apical junction).
Cell junction
Membrane skeleton
Gap junction
Nuclear envelope
Cytoskeleton
Extracellular matrix
Tight junction
Cell signaling