Epithelial Tissue
Chapter 4
Anatomy and Physiology
Liberty High School
Mr. Knowles
Tissue
• Collections of specialized cells
and cell products that perform a
specific function.
Four Types of Tissue
• Epithelial- covers exposed surfaces,
lines passageways, forms glands.
• Connective- fills internal space,
structural support, storage of energy.
• Muscle -contracts for specific
movements.
• Neural- carries information from one
part of the body to another.
Observe my Lunch
on the Front Table!
• List three functions of the
plastic bag.
Epithelial Tissue
• Includes epithelia and glands.
• Epithelium- a layer of cells that
forms a barrier. Epithelia- plural,
many types; Epithelial is the
adjective.
• Examples: surface of skin; lining of
the digestive, respiratory, reproductive
tracts.
Functions of Epithelia
• Provide Physical Protectionprotect surfaces from abrasion,
dehydration, chemical and
biological agents.
• Control Permeability- regulates
molecules that enter or leave
through the surface.
Permeability Can Change!
Callus
Corn
Functions of Epithelia
• Provides Sensation- many
sensory nerves; Ex: smell, taste,
hearing.
• Produce Specialized Secretionsgland cells produce secretions
Some Characteristics
• Cellularity: tightly bound cells
with little space between.
• Polarity: has an exposed surfaceapical surface (faces exterior
surface ) and an attached surfacebasal surface (attached to
underlying tissue). Organelles are
distributed unevenly in these cell.
Characteristics
• Attachment: basal surface of an
epithelium is bound to a thin basement
membrane- produced by the basal
surface of epithelium and underlying
connective tissue.
• Avascularity: epithelia have no blood
vessel; epithelial cells receive nutrients
by diffusion through apical and basal
surfaces.
Characteristics
• Regeneration: cells damaged
or lost at the apical surface are
replaced constantly.
How do epithelial cells do
ALL of this?
The answer is in their
structure!
Function  Structure
Specialized Epithelial Cells
Some epithelial cells:
a. Produce secretions.
b. Help with movement of fluids over
epithelial surface.
c. Help move fluids through the
epithelium.
These cells have a strong polarity (top
and bottom).
Apical Surface Structures
1. Microvillus (i)- small projections of
the cell; a few to many on each cell.
Function: increase surface area (20X)
of epithelial cell (transport specialists).
Location: epithelial surfaces where
there is absorption and secretion; along
digestive and urinary tracts
See Fig. 4-1, p. 110.
Microvilli
Apical Surface Structures
2. Cilia- different internal structure than
microvilli; many, long extensions that
beat in a coordinated fashion.
Function: movement of material
along the epithelium.
Location: respiratory tract (mucus);
fallopian tubes (egg)
Cilia
Apical Surface Structures
3. Stereocilia- similar to microvilli but
longer, but cannot move.
Function: detection of vibration.
Location: male reproductive tract;
receptor cells of inner ear.
Stereocilia
Stereocilia
Show me Ciliated Epithelia in
Action!
Damaged Epithelia and
Emphysema
The Effects of Emphysema
Staying Together!
3 Ways Epithelial Cells Stay
Together:
1. Intercellular Connections
2. Attachment to Basal
Membrane
3. Epithelial Maintenance and
Repair
1. Intercellular Connections
or Cell Junctions
a. Tight Junctions- fusion of cell
membranes of neighboring cells.
Function: block water and solutes
between cells; protection.
Location: near apical surfaces of
cells in digestive tract-keep enzymes
and acids from damaging cells
underneath.
1. Intercellular Connections
or Cell Junctions
b. Desmosomes- strong connections of
proteins (CAMs) between cells.
Function: Act as cross-braces between
cells (tent ropes) to hold the shape of
cells; anchor cell to it’s base.
Found: basal and lateral; superficial
skin and cardiac muscle cells; Ex. Dead
skin comes off as sheet.
1. Intercellular Connections
or Cell Junctions
c. Gap Junctions- interlocking
membrane proteins (connexons) that
form channels between cells.
Function: allow small molecules
and cations to pass between cellscoordinate functions-beating cilia.
Found: lateral; cardiac and smooth
muscle
Connexons or
Channel Proteins
2. Basement Membrane
• A layer of protein fibers to
which epithelia can attach.
• Separates epithelial layer from
connective tissue.
3. Maintenance and Repair
• Epithelial cells must be replaced due
to damage-bacteria, enzymes, toxic
chemicals, etc.
• Use germinative cells (a type of
stem cell) to replace them.
• Located in deepest layer near
basement membrane.
QuickTime™ and a
GIF decompressor
are needed to see this picture.
The Layers of Skin
How many kinds of epithelia
are there?
Classified in Two Ways:
Number of Layers and
Shape of Cell
A. Layers
1. Simple- a single layer covers the B.M.
Characteristics: thin layer, fragile; no
mechanical protection.
Location: lines internal passageways
and compartments. Ex. Walls of blood
vessels; internal surface of lungs.
Function: absorption and secretion;
reduce friction in vessels.
A. Layers
2. Stratified- several layers of cells cover
the B.M.
Characteristics: only one layer contacts
the B.M.; other layers lay on top of these
cells.
Location: surface of the skin; lining of
the mouth.
Function: protect from mechanical and
chemical stress.
B. Shape
1. Squamous- “scale” thin, flat cells; look
like fried eggs laid side by side.
Ex. Simple Squamous Epitheliumwalls of alveoli of lung; walls of blood
vessels and inner heart chamber- called
Endothelium. Ex. Stratified Squamous
Epithelium- surface of skin; lines
mouth, etc.; provides protection.
Simple Squamous Epithelium
Apical View of Simple
Squamous
Simple Squamous: CrossSectional View of Blood Vessel
Simple Squamous: CrossSectional View of Lung Alveoli
Stratified Squamous
Epithelium
Stratified Squamous - Cheek
Cells
Stratified Squamous
Stratified Squamous-Cross
Section, Lower Magnification
Stratified Squamous-Cross
Section, Higher Magnification
B. Shape
2. Cuboidal- hexagonal boxes; nuclei near
center of cells.
Ex. Simple Cuboidal- mostly secretion
and absorption; kidney tubules; salivary
glands.
Stratified Cuboidal- rare in body; lines
the ducts of sweat and mammary glands.
Transitional Epithelium- are a type of
stratified cuboidal; allows expansion
and contraction; lines urinary bladder.
Simple Cuboidal Epithelium
Simple Cuboidal: X-Section of
Kidney Tubules
Transitional Epithelium:
Ureter, Lower Magnification
Transitional Epithelium:
Ureter, Higher Magnification
B. Shape
3. Columnar Epithelial- hexagonal
cells but taller than they are wide;
“columns”; nuclei are crowded near
B.M.
Ex. Simple Columnar- absorption and
secretion; inside small intestine;
secrete protective mucus; may have
microvillie at apical surface.
Simple Columnar Epithelium
B. Shape
3. ColumnarEx. Pseudostratified Columnar- nuclei
not in same plane- appear stratified, but
not. All cells contact the B.M. Foundrespiratory tract- have cilia; line trachea,
nasal cavity.
Stratified Columnar- rare; protective;
line epiglottis and pharynx
Simple Columnar: Small
Intestine (Villi)
Simple Pseudostratified
Pseudostratified Epithelium
Pseudostratified Ciliated
Columnar
Stratified Columnar
Glandular Epithelia
• Endocrine Glands- release
secretions into surrounding interstitial
fluid; they have no ducts.
• Glands may line the digestive tract or
be separate.
• Example- hormones (insulin from the
pancreas)
Glandular Epithelia
• Exocrine Glands- secretions
discharged onto epithelial surfaces;
released into tubular passagewaysducts that empty onto surface of
other epithelial tissues.
• Examples- sweat, saliva, and tears.
QuickTime™ and a
GIF decompressor
are needed to see this picture.
Lets’ see epithelia in
action!
National Geographic
magazine, November 2002
National Geographic video
Skin, November 13, 2002