Course 2.2Lesson 1 of 3

Epithelial tissue

Epithelial tissue covers the body and lines its organs. Its cells are packed closely with little space between them. The kinds are named by shape: squamous (flat), cuboidal (cube), columnar (tall) and ciliated (with hairs). The shape fits the job: thin flat linings let substances pass quickly, while many layers protect.

about 25 min1 simulation2 practice questions1 Python program5 questions to check yourself

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The covering tissues

Animals have four main kinds of tissue: epithelial, connective, muscular and nervous. We begin with the one that covers.

Epithelial tissue covers the outside of the body and lines the inside of organs: the mouth, blood vessels, the lungs and the food pipe. It forms a barrier between the body and the world, or between parts of the body.

The cells are packed closely, with very little space between them. They rest on a thin base, and the layer has no blood vessels.

Kinds of epithelium

Squamous epithelium: flat, thin cells like tiles. In the skin, where there is wear, it is in many layers. In the walls of blood vessels it is one thin layer, so food and gases pass easily.
Cuboidal epithelium: cube-shaped cells, in the kidney tubules and the ducts of salivary glands, where it gives support.
Columnar epithelium: tall, narrow cells, lining the intestine, where they absorb food and release substances.
Ciliated columnar epithelium: tall cells with cilia on top, lining the windpipe. The cilia beat, and push mucus with dust out of the lungs.

Some epithelial cells make a liquid; they form glandular epithelium, as in the salivary gland.

Four kinds of epithelial tissue, each as a row of cells on a base. Squamous: flat cells, found in the skin and the lining of the mouth and of blood vessels. Cuboidal: cube-shaped cells, found in the kidney tubules and salivary glands. Columnar: tall cells, found in the lining of the intestine. Ciliated columnar: tall cells with hairs on top, found in the lining of the windpipe.

Why different shapes?

The shape fits the job. Flat cells are thin, so they protect and let substances through easily. Cube cells support and make substances. Tall cells have room inside for absorbing and releasing. Cilia sweep things along.

You should find that one layer of flat cells, 1 µm thick, takes a thousandth of a second, as in the wall of a capillary. Twenty layers take 400 times as long; that suits the skin, which must protect, not let things through.

Try it in Python

This program is a lookup: give a place in the body, and it names the epithelium and its job.

Practise with new numbers

Common mistakes

Thinking epithelium has blood vessels in it. It has none; it rests on a base.
Mixing up columnar and cuboidal. Columnar cells are tall; cuboidal cells are as tall as they are wide.
Forgetting why the skin has many layers. It suffers wear, so it needs protection more than speed.
Thinking cilia are only on single cells. The windpipe is lined with them.