Tight junction

Tight junction

Diagram of Tight junction
Latin junctio occludens
TH H1.
FMA 67397

Anatomical terminology

Tight junctions, also known as occluding junctions or zonulae occludentes (singular, zonula occludens), are the closely associated areas of two cells whose membranes join together forming a virtually impermeable barrier to fluid. It is a type of junctional complex present only in vertebrates. The corresponding junctions that occur in invertebrates are septate junctions.


Tight junctions are composed of a branching network of sealing strands, each strand acting independently from the others. Therefore, the efficiency of the junction in preventing ion passage increases exponentially with the number of strands. Each strand is formed from a row of transmembrane proteins embedded in both plasma membranes, with extracellular domains joining one another directly. Although more proteins are present, the major types are the claudins and the occludins. These associate with different peripheral membrane proteins such as ZO-1 located on the intracellular side of plasma membrane, which anchor the strands to the actin component of the cytoskeleton. Thus, tight junctions join together the cytoskeletons of adjacent cells.


They perform vital functions:[1]

In human physiology there are two main types of epithelia using distinct types of barrier mechanism. Dermal structures such as skin form a barrier from many layers of keratinised squamous cells. Internal epithelia on the other hand more often rely on tight junctions for their barrier function. This kind of barrier is mostly formed by only one or two layers of cells. It was long unclear whether tight cell junctions also play any role in the barrier function of the skin and similar external epithelia but recent research suggests that this is indeed the case.[4]


Epithelia are classed as "tight" or "leaky", depending on the ability of the tight junctions to prevent water and solute movement:[5]

See also

TEM of negatively stained proximal convoluted tubule of Rat kidney tissue at a magnification of ~55,000x and 80 kV with Tight junction. Note that the three dark lines of density correspond to the density of the protein complex, and the light lines in between correspond to the paracellular space.


  1. Department, Biology. "Tight Junctions (and other cellular connections)". Davidson College. Retrieved 2015-01-12.
  2. Chalcroft, J. P.; Bullivant, S (1970). "An interpretation of liver cell membrane and junction structure based on observation of freeze-fracture replicas of both sides of the fracture". The Journal of Cell Biology. 47 (1): 49–60. doi:10.1083/jcb.47.1.49. PMC 2108397Freely accessible. PMID 4935338.
  3. Guo, P; Weinstein, AM; Weinbaum, S (Aug 2003). "A dual-pathway ultrastructural model for the tight junction of rat proximal tubule epithelium.". American Journal of Physiology. Renal Physiology. 285 (2): F241–57. doi:10.1152/ajprenal.00331.2002. PMID 12670832.
  4. Kirschner, Nina; Brandner, JM (June 2012). "Barriers and more: functions of tight junction proteins in the skin.". Annals of the New York Academy of Sciences. 1257: 158–166. doi:10.1111/j.1749-6632.2012.06554.x.
  5. Department, Biology. "Tight Junctions and other cellular connections". Davidson College. Retrieved 2013-09-20.
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