Epithelium Types and Layer Identification in Histology

Epithelium

Tissue that lines surfaces, covers organs, and is found at free edges

Free edge

An open space (air or lumen) that epithelium lines

First question to identify epithelium

Am I near a free edge?

If tissue is NOT near a free edge

It is connective tissue

Simple epithelium

One row of nuclei lined up

Stratified epithelium

Two or more rows of nuclei lined up

What to focus on when counting layers

Nuclei, not cell borders

Squamous cells

Flat, thin, squished cells

Cuboidal cells

Cube-shaped or square cells

Columnar cells

Tall, rectangular cells

Simple squamous epithelium

One row of nuclei with flat cells

Simple cuboidal epithelium

One row of nuclei with cube-shaped cells

Simple columnar epithelium

One row of nuclei with tall cells

Stratified squamous epithelium

Multiple rows of nuclei with flat surface cells

Stratified cuboidal epithelium

Multiple rows of nuclei with cube-shaped cells

Stratified columnar epithelium

Multiple rows of nuclei with tall surface cells

Pseudostratified columnar epithelium

Appears layered but is actually one layer of tall cells with nuclei at different heights

Why pseudostratified looks stratified

Nuclei are at different levels

Only epithelial tissue that looks stratified but is not

Pseudostratified columnar epithelium