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Epithelial TissuesLocations:

Body coveringsBody liningsGlandular tissue

Functions:ProtectionAbsorptionFiltrationSecretion

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Epithelium CharacteristicsCells fit closely together and often form sheets

The apical surface is the free surface of the tissueThe unattached surface

Can be exposed to exterior or cavity of an organ

The lower surface of the epithelium (the basal lamina) rests on a basement membraneConsists of reticular connective tissuesecures upper layers

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Epithelium CharacteristicsAvascular (no blood supply)

Relies on circulatory system to obtain food and oxygen Surrounding connective tissues supply via diffusion

from nearby capillaries

Regenerate easily if well nourished (through normal cell division)Cells on exterior of the skin are exposed to

friction and other hostile substances and are sloughed off

Classification of EpitheliaTwo name system:

First name = # of layersSecond name = shape of cells

Named using number of cell layers:Simple—one layer

Absorption/secretion/filtration are main functionsStratified—more than one layer

Ideal for protection Often found where there is friction or abuse; durable

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Figure 3.17a Classification and functions of epithelia.

Basalsurface

Apical surface

Basalsurface

Apical surface

Simple

Stratified(a) Classification based on number of cell layers

Epithelial shapesNames using shape of cells

Squamous Flattened, like fish scales

Cuboidal Cube-shaped, like dice

Columnar Column-like

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Figure 3.17b Classification and functions of epithelia.

Squamous

Cuboidal

Columnar

(b) Classification based on cell shape

Figure 3.17c Classification and functions of epithelia.

Remember these general characteristics and you will be able to classify each type a lot easier !!

Diffusion and filtrationSecretion in serous membranes

Protection

Secretion and absorption; ciliatedtypes propel mucus orreproductive cellsSecretion and absorption; ciliatedtypes propel mucus or reproductive cells

Protection; these tissue types are rarein humans

Protection; stretching to accommodatedistension of urinary structures

(c) Function of epithelial tissue related to tissue type

Number of layers

Cell shapeOne layer: simple epithelialtissues

More than one layer: stratifiedepithelial tissues

Squamous

Cuboidal

Columnar

Transitional

Pseudostratified ColumnarSingle layer

some cells are shorter than others, giving a false (pseudo) impression of stratification

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(d) Diagram: Pseudostratified(ciliated) columnar

Photomicrograph: Pseudostratifiedciliated columnar epithelium lining thehuman trachea (560×).

Basementmembrane

Basementmembrane

Pseudo-stratifiedepitheliallayer

Pseudo-stratifiedepithelial layer

Cilia

Connectivetissue

Transitional EpitheliumUnique because of its ability to become

temporarily modified in arrangement and shape

modified stratified squamous epitheliumCan stretch and reboundLocations: urinary system organs

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Figure 3.18f Types of epithelia and their common locations in the body.

Basementmembrane

Basementmembrane

Connectivetissue

Transi-tionalepithelium

Transitionalepithelium

(f) Diagram: TransitionalPhotomicrograph: Transitional epithelium lining ofthe bladder, relaxed state (270×); surface rounded cellsflatten and elongate when the bladder fills with urine.

Glandular EpitheliumTwo major gland types:

Endocrine gland Ductless; secretions diffuse into blood vessels All secretions are hormones Examples include thyroid, adrenals, and pituitary

Exocrine gland Secretions empty through ducts to the epithelial

surface Include sweat and oil glands, liver (bile duct), and

pancreas (digestive enzymes), mammary glands (milk) Includes both internal and external glands

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