Junctional complex

Junctional complex is a structure found in epithelial cells and endothelial cells that serves to connect cells together and maintain the integrity of tissues. It is composed of three main components: tight junctions, adherens junctions, and desmosomes.

Tight Junctions

Tight junctions, also known as zonula occludens, are the most apical component of the junctional complex. They form a continuous, belt-like seal around cells and serve as a barrier that prevents the leakage of molecules and ions through the space between cells. They are composed of a network of sealing strands, each strand acting as a barrier to diffusion.

Adherens Junctions

Adherens junctions, or zonula adherens, are located just below the tight junctions. They provide strong mechanical attachments between adjacent cells through interaction of their cytoskeletons. They are formed from cadherin proteins, which bind cells together.

Desmosomes

Desmosomes are localized patches that hold cells together like a snap between a pair of jeans. They are found below the adherens junctions and are particularly abundant in tissues that experience a lot of stress, such as the skin and heart muscle. Desmosomes are composed of desmoglein and desmocollin proteins.

Function

The primary function of the junctional complex is to provide structural support to tissues and organs. By connecting cells together, they help to maintain the integrity of tissues and prevent cells from being pulled apart. In addition, they also play a role in signal transduction, cell proliferation, and differentiation.

Clinical Significance

Alterations in the structure or function of the junctional complex can lead to a variety of diseases. For example, mutations in the genes encoding for desmosomal proteins can lead to skin diseases and heart disorders. Similarly, disruption of tight junctions can lead to leaky gut syndrome and other gastrointestinal disorders.