EPITHELIAL
TISSUE
Characteristics
&
classification
Cell Specialization
Single cell organisms must operate independently.
 Cells in multi-cellular organisms do not operate independently.
 Cells become specialized
 Specialization allows body to function in advanced ways.

General Tissue
Groups of cells that are similar in structure and perform a
common function.
 Four types





Epithelial = covering
Connective = support
Muscle = movement
Nervous = control
Epithelial tissue
 A sheet of cells that covers a body surface or lines a
body cavity.
 Occurs as:
Covering and lining
 Glandular

Covering and lining
 Outer layer of skin.
 Lines open cavities of cardiovascular, digestive and
respiratory systems.
 Covers walls and organs of ventral cavity.
Glandular
 Forms the glands in the body.
Functions of Epithelial tissue
 Forms
boundaries between different
environments.
 Nearly all substances given off or
received by body must pass through
epithelial tissue.
More Functions
 Protection
 Absorption
 Filtration
 Excretion
 Secretion
(specialty of glands)
 Sensory reception
Special Characteristics
o
Cellularity
o
o
Composed almost entirely of closely
packed cells. Little to no extracellular
material between them.
Specialized contacts
o
Fit close together to form continuous
sheets.
More….
o
Polarity
o
All have APICAL surface (exposed to
exterior) and a BASAL surface (attached to
connective tissue)
Basement Membrane
o
Basal Lamina = thin supporting sheet
beneath the basal surface.
o
Functions as a selective filter, determining what
can pass from connective tissue below into
epithelial layer.
Reticular Lamina = layer of collagen fibers
beneath the basal lamina
o Basement Membrane = both layers together.
o
o
o
Reinforces the epithelial sheet by helping it to
resist tearing and stretching.
Defines the boundary of epithelial layer.
Even more….
o
Supported by Connective tissue
o
All rest on and are supported by
connective tissue
But wait, there’s more!
o
Innervated, but avascular
o
o
It has nerve endings, but no blood vessels.
Regeneration
o
Ability to rapidly replace damaged or worn
out cells.
Classification of Epithelia
 Each
epithelium is given two names.
 First
indicates number of cell layers.
 Second describes cell shape.
 Based
on cell layers there are two types
 Simple
= single layer
 Stratified = two or more layers
Classification cont.

Shapes = 3 types



Squamous = flattened, scale like
Cuboidal = boxlike, as tall as they are wide
Columnar = tall and column shaped
Shape of nucleus matches shape of cell.
 Nuclear shape can help identify type of
tissue.
 Stratified epithelia named after type of cell on
apical surface.

Simple Squamos
Simple Cuboidal
Simple Columnar
Pseudostratified Columnar
Stratified Squamos
Stratified Columnar
Transitional epithelium