Which junction seals apical surfaces to prevent leakage?

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

Answer: (D)

Preventing leakage between neighboring epithelial cells at the apical surface is achieved by tight junctions. They form a belt-like seal right at the apical region where cells meet, made of transmembrane proteins like claudins and occludins that connect to scaffolding proteins inside the cell. This seal blocks the paracellular pathway, keeping the lumen’s contents from seeping between cells and helping maintain distinct apical and basolateral membrane domains. Gap junctions are channels that allow direct communication between neighboring cells, not barriers to leakage. Desmosomes provide strong mechanical adhesion, not a seal, and adherens junctions mainly link cadherin receptors to actin networks to maintain tissue structure. So, the apical barrier that prevents leakage is the tight junction.