What is the primary function of tight junctions between epithelial cells?

• A. Seal adjacent cells to prevent movement of substances
• B. Allow communication via pores
• C. Provide structural support through cytoskeleton
• D. Promote diffusion between cells

Answer: (A)

Tight junctions form a seal between neighboring epithelial cells, creating a barrier that stops fluids and solutes from bypassing the cells by slipping through the space between them. This paracellular barrier is essential for controlling what passes from the lumen into underlying tissues and helps maintain distinct apical and basolateral surfaces. The proteins that make up these junctions—like claudins and occludins—link to the actin cytoskeleton to create this continuous seal around each cell.

This function is distinct from allowing intercellular communication, which is done by gap junctions that form channels between cells, or from providing mechanical strength through other junctions such as desmosomes or adherens junctions that primarily anchor cells together. It’s also opposite to promoting diffusion between cells, which tight junctions actively prevent.

So the primary role is to seal adjacent cells to prevent movement of substances between them.