Which junction type is most critical for maintaining a seal between epithelial cells in the urinary bladder to prevent leakage during distension?

• A. Adherens junctions
• B. Tight junctions at the apical region
• C. Gap junctions
• D. Desmosomes

Answer: (B)

Tight junctions create a seal between epithelial cells, forming a belt-like barrier right at the luminal (apical) surface. In the urinary bladder, the epithelium must remain watertight as the tissue distends; the apical tight junctions seal the paracellular space so urine cannot leak between cells, even when the lining stretches. This barrier function is what prevents leakage during distension.

Adherens junctions and desmosomes contribute to mechanical cohesion, helping cells stay attached under stretch, but they do not seal the space between cells. Gap junctions permit direct cytoplasmic communication and transport of small molecules, not barrier formation.