What are gap junctions and why are they important in epithelia?

• A. Anchor cells to each other through desmosomes
• B. Intercellular channels that allow diffusion of ions and small molecules, enabling coordinated cell function across an epithelium
• C. Produce mucus on surfaces
• D. Form tight seals to prevent paracellular transport

Answer: (B)

Gap junctions are intercellular channels that connect neighboring epithelial cells, formed by connexin proteins that align to create a continuous pore between the cytoplasms of adjacent cells. Through these channels, ions and small signaling molecules (such as Ca2+, cAMP, and IP3) can diffuse directly from one cell to another, allowing rapid electrical and chemical coupling. In epithelia, this means cells can coordinate transport processes and other responses across the whole sheet, behaving more like a coordinated unit rather than isolated cells. The other options describe different structures: desmosomes that anchor cells; mucus production by secretory cells; and tight junctions that seal the paracellular space. Thus, intercellular channels enabling diffusion of ions and small molecules across the epithelium best captures the role of gap junctions.