Terminal bar

Terminal bar is a term used in histology to describe a region where the lateral membranes of two adjacent cells join together. It is a characteristic feature of certain types of epithelial cells, particularly those found in the gastrointestinal tract and the urinary system. The terminal bar is not a single structure, but rather a complex of several different types of cell junctions, including tight junctions, adherens junctions, and desmosomes.

Structure and Function

The terminal bar is composed of several different types of cell junctions, each with its own specific structure and function.

Tight junctions, also known as zonula occludens, are the most apical component of the terminal bar. They form a continuous, belt-like seal around the cell and serve to prevent the passage of molecules and ions through the space between cells.

Adherens junctions, or zonula adherens, are located just below the tight junctions. They are responsible for maintaining the shape and integrity of the tissue by linking the actin cytoskeletons of adjacent cells.

Desmosomes, also known as macula adherens, are scattered along the lateral cell membrane below the adherens junctions. They provide strong adhesion between cells, helping to resist shearing forces.

Clinical Significance

Alterations in the structure or function of the terminal bar can lead to a variety of pathological conditions. For example, loss of tight junctions can result in increased permeability of the epithelium, allowing harmful substances to pass into the body. Similarly, defects in adherens junctions or desmosomes can compromise the structural integrity of the tissue, leading to conditions such as epidermolysis bullosa, a group of genetic conditions that cause the skin to become very fragile and to blister easily.

See Also

• Cell junction
• Epithelium
• Tight junction
• Adherens junction
• Desmosome