Epithelium: classification (the table to know) !
- Tissue
Epithelium is the sheet of tightly packed cells that covers the body, lines its cavities and tubes, and forms glands.
Updated 2026-11-01
See it in 3D: Skin · Esophagus · Trachea · Kidneys · Urinary bladder
What it is
Epithelium is one of the four basic tissues. Its cells sit close together with almost no matrix between them, have a free (apical) surface and a basal surface anchored to a basement membrane, and carry no blood vessels of their own. It is named by two things: the number of layers (simple or stratified) and the shape of the surface cells (squamous, cuboidal or columnar). Knowing which epithelium lines which organ is the key to identifying organs on a slide.
Key facts
- Simple = one layer; stratified = two or more layers, named after the shape of the top layer.
- Pseudostratified looks layered because its nuclei sit at different heights, but every cell touches the basement membrane.
- Transitional epithelium (urothelium) changes shape as the bladder fills.
- Epithelium is avascular: it is fed by diffusion from the connective tissue underneath.
- Polarity: the apical surface may carry microvilli or cilia; the basal surface rests on the basement membrane; the lateral surfaces are joined by junctions.
Function
- Protection
- Absorption and secretion
- Filtration and diffusion
- Excretion
- Sensory reception (taste buds, olfactory and retinal neuroepithelium)
Covering epithelia: type, where it is found, what it does
| Type | Where | Function |
|---|---|---|
| Simple squamous | Alveoli (type I pneumocytes), endothelium, mesothelium, parietal Bowman capsule | Diffusion and filtration |
| Simple cuboidal | Kidney tubules, thyroid follicles, small gland ducts, ovarian surface | Secretion and absorption |
| Simple columnar | Stomach, small and large intestine, gallbladder; ciliated in the uterine tube | Absorption, secretion, moving the ovum |
| Pseudostratified columnar | Trachea and bronchi (ciliated, with goblet cells); epididymis (stereocilia) | Mucociliary clearance; absorption |
| Stratified squamous, non-keratinized | Oral cavity, esophagus, vagina, ectocervix, cornea | Resists abrasion on moist surfaces |
| Stratified squamous, keratinized | Epidermis of the skin | Barrier against water loss, friction and microbes |
| Stratified cuboidal / columnar | Ducts of sweat and salivary glands; parts of the male urethra; conjunctiva | Protection of ducts (uncommon types) |
| Transitional (urothelium) | Renal calyces and pelvis, ureters, bladder, proximal urethra | Stretches and stays impermeable to urine |
Clinical notes
- Metaplasia swaps one epithelium for another: in Barrett esophagus the stratified squamous lining becomes intestinal-type columnar with goblet cells after chronic acid reflux.
- Smokers' bronchi can change from ciliated pseudostratified to stratified squamous epithelium (squamous metaplasia).
- Carcinomas are cancers of epithelium; the type of epithelium they come from shapes their name (squamous cell carcinoma, adenocarcinoma, urothelial carcinoma).
Test yourself
Think of the answer, then tap the question to see it.
What two features are used to name a covering epithelium?
The number of cell layers (simple or stratified) and the shape of the cells at the surface (squamous, cuboidal or columnar).
Why is the epithelium of the trachea called pseudostratified?
Its nuclei lie at different heights so it looks layered, but every cell rests on the basement membrane, so it is a single layer.
Which epithelium lines the lumen of the esophagus?
Stratified squamous non-keratinized epithelium.
How does epithelium get oxygen and nutrients if it has no blood vessels?
By diffusion from capillaries in the connective tissue below the basement membrane.
See it in 3D
The structures of Durgical's 3D anatomy where it is found.
Related
- Simple, stratified, pseudostratified and transitional epithelium
- Glands: exocrine vs endocrine, secretion types
- Basement membrane
- Cell junctions: tight, adherens, desmosomes, gap, hemidesmosomes
- Cilia, microvilli and stereocilia
- Cell adaptations: hypertrophy, hyperplasia, atrophy, metaplasia
Related conditions
Educational content on normal microscopic structure and its clinical relevance; no substitute for studying slides or for a health professional's advice.
Sources: 4.2 Epithelial Tissue (OpenStax, 2022); Epithelial Tissue (National Cancer Institute, SEER Training Modules, 2024); Body Tissues (National Cancer Institute, SEER Training Modules, 2024).
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Representative model, for educational purposes only.