Types of Epithelium

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Classification of Epithelia

• All epithelial tissues have two names– One indicates number of cell layers

• Simple epithelia = single layer of cells• Stratified epithelia = two or more layers of cells

– Shape can change in different layers

– One indicates shape of cells• Squamous• Cuboidal• Columnar

• In stratified epithelia, epithelia classified by cell shape in apical layer

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Figure 4.2a Classification of epithelia.

Basal surfaceStratified

Classification based on number of cell layers.

Basal surfaceSimple

Apical surface

Apical surface

SIMPLE SQUAMOUS EPITHELIUM

Single layer of thin, flattened cells Broad thin nucleus (disc shaped)

Fxn: allows passage of materials by diffusion and filtration where protection is not important

Examples: air sacs (alveoli) Capillary walls, lining the heart, lining of ventral body

cavity, kidney glomeruli

Simple Cuboidal Epithelium

Single layer of cube shaped cellsCentrally located, spherical nucleus

FXN: Secretion and absorption

Ex: ovaries, kidney tubules, salivary glands, thyroid, pancreas, liver

Simple Columnar Epithelium

Elongated (longer than they are wide)

Nuclei located near/on basement membrane

(often you will find microvilli on surface)

(also find goblet cells)

Simple Columnar

Found: Lining most of Digestive tract (non-ciliated type), gallbladder, excretory ducts of some glands; small bronchi, uterine tubes, regions of uterus

Function: Absorption, secretion of mucous, enzymes and other substances

Simple Columnar

Stratified Squamous Epithelium

Multiple layer of squamous cells Two Main Types 1. Keratinizedouter layer of epidermis of the

skin.2. Non-keratinized Ex: mouth, throat, anus(cells on free surface remain alive) Definitely Protection!!

Stratified cuboidal Epithelium

2-3 layers of cuboidal cells (form lining of lumen)

-protection -sweat glands, mammary glands, salivary

glands, glands of pancreas

Stratified Columnar

RARE!!!

2-4 layers of elongated cellsProtectionEx: Male urethra, Vas deferens, parts of

pharynx

Pseudostratified Columnar

Appears to be stratified or layered. (BUT THEY ARE NOT)!!

Cell nuclei are actually at different levels in the row, but all cells are attached to the basement membrane.

Usually, but not always ciliated. Protection and Secretion

Ex: Trachea lining in the respiratory system

Transitional Epithelium

Specialized epithelium designed to change in response to increased tension. Stretches, changing apical cuboidal cells into squamous cells.

Many Layers

Ex: Bladder, ureters, parts of urethra

Transitional