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Human Body Study

Epithelial Tissue

The covering and lining tissue — it forms the body’s surfaces, inside and out.

The four tissue types in a generalized organ wall A layered cross-section showing the four tissue types stacked as they combine to build an organ. Each label links to the article for that type: epithelial, connective, muscle and nervous tissue. basement membrane a generalized organ wall free surface Epithelial tissue Connective tissue Muscle tissue Nervous tissue The four tissue types, layered as they combine to build an organ — schematic, not to scale.

Where it is

Section titled “Where it is”

The outer layer of skin, the lining of the entire digestive tract, the airways, blood vessels, and body cavities, and the working tissue of glands.

How it is classified

Section titled “How it is classified”

By cell shape — squamous (flat), cuboidal, or columnar — and by layering — simple (one layer) or stratified (many layers).

What it does

Section titled “What it does”
  • Protection — shields underlying tissue from wear, microbes, and chemicals.
  • Absorption — takes up nutrients, especially in the gut.
  • Secretion — glands are made of epithelium; they release hormones, enzymes, sweat, and mucus.
  • Filtration and exchange — thin epithelia allow gases and fluids to pass.

Key idea

Section titled “Key idea”

Epithelium always has a free surface on one side and sits on a “basement membrane” on the other. It has no blood supply of its own and is fed by the tissue beneath.