Classification of Epithelium

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

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