Tissues in Action
Linings and coverings
Learn the tissues that line and cover the body.
Epithelial tissue is the body's covering and lining. It covers you on the outside (skin) and lines the inside of organs: the mouth, lungs, blood vessels, intestine.
Its cells are packed close together with almost no gaps. That keeps out germs, cuts down water loss, and controls what is absorbed (taken in), secreted (given out) and moved across it.
Each type is shaped for its job:
| Job | What the cells are like | Where |
|---|---|---|
| Exchange | One layer of thin, flat cells, so liquids and gases cross quickly | Blood vessels, lungs |
| Protection | Many layers; the outer ones flat and tightly packed | Skin, mouth, food pipe (oesophagus) |
| Secretion | Cube-shaped or column-shaped cells that make mucus, enzymes, hormones, sweat, saliva | Salivary and sweat glands, stomach lining |
| Senses | Receptor cells with tiny hairs (cilia) | Nostrils, taste buds, inner ear |
| Absorption | One layer of tall, pillar-like cells, often with tiny hair-like parts | Small intestine |
Notice the pattern: where things must pass through quickly, the lining is thin; where the body must be guarded, it is thick; where food must be taken in, the cells are tall.
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