Glossary
epithelial tissue
Epithelial tissue covers and lines surfaces, forms glands, and sits on a basement membrane — it has no blood vessels of its own.
Epithelial tissue covers the body's surfaces, lines its cavities and tubes, and forms its glands. The cells are packed close with almost no material between them, which is what makes the tissue a barrier, and it sits on a thin basement membrane that anchors it to the connective tissue underneath. It carries no blood vessels of its own; oxygen and nutrients arrive by diffusion from the tissue below. Shape and layers name it. Squamous cells are flat, cuboidal are about as tall as they are wide, columnar are taller than wide. One layer is simple, thin enough to exchange gases, as in the air sacs of the lung; several layers are stratified, which is what an abrasion-prone surface such as the skin needs. A gland is epithelium folded into the tissue beneath it.
Taught in
Related terms
- tissue — A tissue is a group of similar cells with a shared job and the material between them — the level between a cell and an organ.
- epidermis — The epidermis is the outer, avascular layer of the skin — stratified epithelium that renews from its base and makes keratin and melanin.
- dermis — The dermis is the layer under the epidermis: connective tissue carrying the blood vessels, nerves, glands and hair follicles the skin needs.
- alveolus — An alveolus is one of the thin-walled air sacs at the end of the airway, where oxygen and carbon dioxide move between the air and the blood.
Source: The anatomy and physiology guide in this course, whose organ and tissue descriptions follow the US National Cancer Institute's SEER Training Modules and MedlinePlus consumer health pages. Both are US federal government material, not subject to copyright in the United States. The definition above is written for this course in our own words. (SEER Training Modules accessed 2026-10-26; definition written 2026-10-27)