What are the 7 types of epithelial tissue?

The seven types of epithelial tissue usually taught in anatomy and histology courses are:

1. Simple squamous epithelium: one layer of flat cells
2. Simple cuboidal epithelium: one layer of cube-shaped cells
3. Simple columnar epithelium: one layer of tall cells
4. Pseudostratified columnar epithelium: one layer that looks like several
5. Stratified squamous epithelium: many layers, flat at the surface
6. Stratified cuboidal epithelium: usually two or three layers of cube-shaped cells
7. Transitional epithelium (urothelium): many layers that change shape as the organ stretches

Some textbooks add an eighth, stratified columnar epithelium, which is rare in the body. This guide covers what each type looks like down the microscope, where you’ll find it, and how to tell them apart on a slide.

How epithelia are named

Epithelium is the tissue that covers body surfaces, lines hollow organs and cavities, and forms most glands. Its cells sit close together with very little material between them, and the whole sheet rests on a thin basement membrane. Below that is connective tissue.

The names combine two features:

• Number of layers. Simple means one layer of cells. Stratified means two or more. Pseudostratified means one layer that only looks like several.
• Shape of the cells. Squamous cells are flat. Cuboidal cells are about as tall as they are wide. Columnar cells are taller than they are wide.

In stratified epithelium the deep cells are often a different shape from the surface cells. By convention the tissue is named after the surface layer. Skin epidermis has cuboidal-looking cells at its base, but it’s called stratified squamous because the top cells are flat.

The seven types in detail

Simple squamous epithelium

• Looks like: a very thin layer of flat cells. In a cross-section you often see only a thin line with flattened nuclei bulging slightly. Viewed face-on, the cells look like irregular floor tiles.
• Found in: the air sacs (alveoli) of the lungs, the lining of blood and lymph vessels (endothelium), and the lining of body cavities (mesothelium).
• Does: allows substances to pass through quickly by diffusion and filtration. It gives little protection.

Simple cuboidal epithelium

• Looks like: one row of square-looking cells, each with a round, central nucleus. In a cross-section of a tubule it forms a ring of cells around a small central space.
• Found in: kidney tubules, small gland ducts, the thyroid follicles and the surface of the ovary.
• Does: secretion and absorption.

Simple columnar epithelium

• Looks like: one row of tall cells with oval nuclei, usually lined up near the base. The free surface may carry microvilli (a fuzzy “brush border”) or, in some places, cilia. Pale, cup-shaped goblet cells that secrete mucus are often scattered among them.
• Found in: most of the digestive tract from the stomach to the rectum, and the gallbladder. A ciliated form lines the uterine tubes.
• Does: absorption and secretion of mucus and enzymes.

Pseudostratified columnar epithelium

• Looks like: at first glance, several layers. The nuclei sit at different heights, which makes it look stratified. In fact every cell touches the basement membrane, though not every cell reaches the surface, so it’s technically a single layer. In the airways it is usually ciliated and has goblet cells.
• Found in: the trachea and much of the upper respiratory tract.
• Does: secretes mucus and moves it along with beating cilia, carrying trapped dust and microbes away from the lungs.

Stratified squamous epithelium

• Looks like: many layers of cells. The deep cells are roughly cuboidal and the cells become flatter towards the surface. It comes in two forms:
  • Keratinized, as in the epidermis of the skin, where the surface layers are dead, flattened cells filled with keratin and have no nuclei.
  • Non-keratinized, as in the mouth, oesophagus and vagina, where the surface cells stay alive and keep their nuclei.
• Does: protects against abrasion. The keratinized form also limits water loss.

Stratified cuboidal epithelium

• Looks like: usually two or three layers of cuboidal cells.
• Found in: the ducts of larger glands, such as sweat glands, salivary glands and mammary glands.
• Does: mainly protection, with some secretion. It’s uncommon, and you’ll mostly meet it in gland ducts on prepared slides.

Transitional epithelium (urothelium)

• Looks like: several layers, with large, rounded, sometimes dome-shaped surface cells when the organ is relaxed. Some surface cells have two nuclei. When the bladder is stretched, the layers look thinner and the surface cells flatten.
• Found in: the urinary bladder, ureters and part of the urethra.
• Does: stretches without tearing and forms a barrier against urine.

Why some lists say eight (or four)

You’ll see different numbers because textbooks group these tissues in slightly different ways.

• Eight types: some sources add stratified columnar epithelium, found in small patches such as parts of the male urethra, some large gland ducts and the conjunctiva of the eye. It’s rare, so many introductory courses leave it out.
• Glandular epithelium is sometimes treated as a separate category because it forms glands rather than a covering sheet.
• Four types: “four types of tissue” is a different question. The four basic tissue types in the body are epithelial, connective, muscle and nervous tissue. Epithelium is just one of them. Our beginner’s guide to histology explains all four.

How to identify epithelium on a slide

If you’re working through a box of prepared slides, a systematic approach saves a lot of guessing. Most commercial slides use H&E staining (hematoxylin and eosin), which colours nuclei blue-purple and cytoplasm pink.

1. Find the free surface. Epithelium faces a space: the outside of the body, the inside of a tube, or a cavity. Look for an edge with nothing above it, or a central hole (the lumen).
2. Find the basement membrane. It’s the boundary between the tightly packed epithelial cells and the looser connective tissue underneath. It’s often hard to see in H&E, so look for the change in texture.
3. Count the layers of nuclei between the basement membrane and the surface. One neat row suggests simple epithelium. Several rows suggest stratified, or possibly pseudostratified.
4. Look at the shape of the top cells. Flat, cube or column.
5. Check the surface. A fuzzy fringe may be cilia or a brush border of microvilli. Pale, bulging goblet cells point to columnar or pseudostratified epithelium.
6. Use the organ as a clue. If the label says trachea, pseudostratified ciliated columnar is the likely answer. If it says bladder, think transitional.

Common pitfalls

• Pseudostratified vs stratified. In pseudostratified epithelium the nuclei are scattered at different heights, but the cells don’t flatten towards the surface and there are often cilia. Stratified squamous gets steadily flatter towards the top.
• Oblique cuts. If a section cuts through a tube at an angle, a simple epithelium can look thicker and multi-layered. Look at several areas of the slide before you decide.
• Damage from preparation. Shrinkage, folds, tears and lifted surface layers can all mislead you. Our guide to microscopy artifacts shows how to recognise them.
• Transitional vs stratified squamous. Transitional epithelium has rounded, plump surface cells rather than thin, flat ones, at least when the bladder isn’t fully stretched.

Seeing epithelium yourself

You don’t need a histology lab to see real epithelial cells. The cells you gently scrape from the inside of your cheek with a clean toothpick come from the surface of non-keratinized stratified squamous epithelium. On a slide they appear as single, flat, irregular cells with a small central nucleus. They’re very pale unless stained, so a drop of methylene blue helps. Our methylene blue staining guide walks through the cheek cell method. A scrape shows loose surface cells, though, not the layered structure, which you can only see in a section.

To see the full arrangements, prepared slides are the practical option. Many educational suppliers sell individual slides or sets. Useful ones include:

A compound microscope with 10x and 40x objectives (100x and 400x total magnification with a 10x eyepiece) is enough for all of these. Start at low power to find the surface, then move up to see the cell shapes.

Quick reference