46
UNIT 2
Basic Tissues
Types of
Epithelia
Number of
Layers
Type of Cells in the
Epithelium
Apical
Surface
Main Locations
(Lining)
Main Functions
Simple
squamous
epithelium
One
Flattened, squamous
epithelial cells
Smooth
Cornea, blood, and
lymphatic vessels—
endothelium; surface
of body cavities—
mesothelium (pleural,
pericardial, peritoneal);
alveoli in the lung
Fluid transport,
lubrication, and
exchange
Simple
cuboidal
epithelium
One
Cuboidal epithelial cells
(height equal to width)
Smooth/short
microvilli;
long microvilli
depending on
location
Kidney tubules, thyroid
follicles; small ducts
of exocrine glands and
surface of ovary
Absorption,
secretion, and
transportation
Simple
columnar
epithelium
One
Absorptive columnar cells
and secretary cells, such as
goblet cells
Mostly
microvilli;
cilia in some
locations
Most of digestive
tract and gallbladder;
oviducts and ductuli
efferentes
Secretion,
absorption,
protection, and
transportation
Pseudostrati± ed
columnar
epithelium
One
Ciliated columnar cells,
goblet cells, and short basal
cells not reaching lumen; all
cells rest on the basement
membrane
Mostly cilia;
stereocilia
in some
locations
Most of respiratory
tract; ductus deferens
and epididymis
Secretion,
transportation,
and absorption
Strati± ed
squamous
epithelium
Several
Flattened surface cells,
polygonal cells in the
middle layers, and cuboidal
cells in basal layer
Keratinized
or nonkerati-
nized surface
layer
Epidermis of the skin;
oral cavity, epiglottis,
and esophagus; vagina
Protection
(barrier)
Strati± ed
cuboidal
epithelium
Two to three
Cuboidal cells
Mostly
smooth
Large ducts of
exocrine
glands and ducts
of sweat gland (not
common type)
Transportation
Strati± ed
columnar
epithelium
Two to three
Low columnar surface cells
and cuboidal basal cells
Smooth
Large ducts of exocrine
glands; conjunctiva of
the eye (not common
type)
Transportation
and protection
Transitional
epithelium
Four to six layers
(relaxed); two
to three
layers
(distended)
Dome-shaped surface cells
(relaxed), polygonal in the
middle layer, cuboidal cells
in the basal layer
Smooth
Urinary tract
Transportation
and protection
(distensible
property)
TABLE 3-2
Epithelium
SYNOPSIS 3-3
Functions of Epithelial Tissue
Promotes gliding between two surfaces (mesothelium of pleural cavity [Fig. 3-2A,B]).
Senses changes in blood pressure, oxygen tension, and blood fl
ow and controls blood coagulation (endothelium of blood
vessels [Fig. 3-3A,B]).
Pumps the excess fl uid out of the stroma and keeps the cornea clear (simple squamous epithelium in cornea).
Mediates gas exchange (type 1 pneumocytes and simple squamous epithelium in the alveoli of the lung).
Absorbs material from a lumen (simple cuboidal epithelium in kidney and simple columnar epithelium in small and large
intestines [Figs. 3-6A,B and 3-7A,B]).
Transports material along a surface (pseudostrati± ed ciliated columnar epithelium in the respiratory tract [Fig. 3-9A,B]).
Provides conduit for fl uid (simple and strati± ed cuboidal and columnar epithelia forming ducts of some large exocrine
glands [Fig. 3-15A,B]).
Protects the body from abrasion and injury (strati±
ed squamous epithelium in the skin and esophagus [Figs. 3-13A,B and
3-14A,B]).
Becomes highly distensible when the bladder is ±
lled with urine and the tissue is stretched (transitional epithelium in
bladder [Fig. 3-17A–C]).
Secretes mucus, hormones, and proteins (secretory epithelium, glands [Figs. 3-18 and 3-19]).
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