What type of junction provides an impermeable barrier between epithelial cells?

• A. Gap junctions
• B. Tight junctions
• C. Desmosomes
• D. Adherens junctions

Answer: (B)

Tight junctions are specialized connections between epithelial cells that create a seal, effectively preventing the passage of substances between the cells. This impermeable barrier is crucial for maintaining the distinct environments on either side of the epithelial layer, such as in the lining of the intestines where it is important to keep digestive enzymes and nutrients separate from the bloodstream.

In addition to providing a barrier, tight junctions help maintain the polarity of the cells by preventing the diffusion of proteins and lipids between the apical and basolateral surfaces of the epithelial cells. This characteristic is particularly important in tissues where selective absorption and secretion are essential for proper function.

In contrast, gap junctions facilitate intercellular communication by allowing ions and small molecules to pass directly between adjacent cells, while desmosomes and adherens junctions provide structural support and strength by anchoring the cells together but do not create a barrier to substance movement.