Classification of Epithelium

Each epithelial type has two parts to its name: 1) Number of layers present

Classification of Epithelium Each epithelial type has two parts to its name: 1) Number of layers present 2) General shape of the cell

Number of Layers Those having a single layer are called simple Those having multiple layers are called stratified.

General Shape Epithelial cells have 3 general shapes: Squamous

General Shape Epithelial cells have 3 general shapes: Squamous Cuboidal

General Shape Epithelial cells have 3 general shapes: Squamous Cuboidal Columnar

Simple Squamous Epithelium These are very thin cells which are typically are very permeable. Diffusion is a high priority.

2 epithelial surfaces have special names: Endothelium – cells that line the blood vessels, heart and lymph vessels

2 epithelial surfaces have special names: Endothelium – cells that line the blood vessels, heart and lymph vessels Mesothelium – cells that line the serous membranes and their organs.

Simple Squamous Epithelium

Mesothelial Cells

Simple Cuboidal Epithelium Their role is secretory and absorption. They have a cube shape with a centrally placed nucleus.

Simple Columnar Epithelium These are a single layer of oblong cells which are tightly packed. Seen with organs involved with absorption, they are usually modified with microvilli or cilia.

Pseudo stratified Columnar Epithelium These are columnar epithelial cells that vary in height The nuclei do not appear at the same height

Stratified Epithelium These have multiple layers and are more durable

Stratified Epithelium These have multiple layers and are more durable Their major function is protection.

Stratified Epithelium These have multiple layers and are more durable Their major function is protection. Mitotic figures are not uncommon in the basilar levels.

Stratified Squamous Epithelium This is the most common type of stratified epithelium. The upper most layers are flat and are made up of dead or dying cells

Stratified Squamous Epithelium The major example is skin The outer most layers contains cells filled with keratin Correctly called keratinized squamous epithelium

Stratified Squamous

Stratified cuboidal and columnar epithelium Neither of these is very common Stratified cuboidal is found in some sweat ducts and in mammary glands

Stratified cuboidal and columnar epithelium

Transitional Epithelium This type has cells that are cuboidal in the basal layer The shape of the apical cells varies. Epithelial cells that can stretch flat