Which tight junctions are the most apical?

• A. Zonula occludens
• B. Zonula adherens
• C. Macula adherens
• D. Gap junctions

Answer: (A)

The main idea is where the different cell–cell junctions sit along the apical–basal axis of epithelial cells. Tight junctions, called zonula occludens, form a belt right at the very top of the lateral membranes, just below the apical (luminal) surface, creating a seal that limits paracellular diffusion and helps maintain polarity. That apical position distinguishes them from other junctions: zonula adherens (adherens belt) lie just below the tight junctions to help hold cells together, macula adherens (desmosomes) are deeper and provide strong adhesion, and gap junctions are channels embedded in the lateral membranes for intercellular communication. So the most apical tight junctions are zonula occludens.