What is the primary function of epithelial tissue?

• A. To absorb nutrients
• B. To transport signals
• C. To provide immunity
• D. To cover body surfaces, line cavities, and form glands

Answer: (D)

Epithelial tissue is built to cover and line everything: it forms the outer layer of the skin, lines the walls of body cavities and organs, and lines ducts and hollow passages. It also creates glands, from which secretions such as mucus, enzymes, or hormones are produced. This covering and lining function provides protection, acts as a barrier, and supports secretion and selective absorption in specialized areas. While some epithelia can absorb nutrients or participate in other tasks, the overarching, defining role of epithelial tissue is to cover surfaces, line cavities, and form glands. The other options describe activities tied to other tissue systems (nervous or immune) or to specific situations within epithelia, not the general function of epithelial tissue.