Cell junctions are structures that connect adjacent cells, characteristically in epithelial tissue, and they are classified by two orthogonal criteria: the mechanical relationship they impose between cells and the permeability they permit in the intercellular space. Three principal types are distinguished — tight junctions, which form a continuous watertight seal barring water, ions, and other molecules from passing between cells; desmosomes, which anchor into the cytoskeleton as discrete spot attachments that confer mechanical strength while leaving the intercellular gap permeable; and gap junctions, which form direct tunnels between cell interiors permitting ionic flow and hence electrical coupling. The concept belongs to cell biology and histology, and it grounds the discipline's principle that tissue-level properties — barrier function, resistance to mechanical stress, and propagation of electrical signals — follow from the junction types a tissue expresses.
Cell junctions are structures that connect adjacent cells, characteristically in epithelial tissue, and they are classified by two orthogonal criteria: the mechanical relationship they impose between…