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Epithelial Tissue
Chapter 4
Anatomy and Physiology
Liberty High School
Mr. Knowles
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Tissue
• Collections of specialized cells and cell products that perform a specific function.
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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.
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Observe my Lunch on the Front
Table!• List three functions of the
plastic bag.
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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.
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Functions of Epithelia• Provide Physical Protection- protect
surfaces from abrasion, dehydration, chemical and biological agents.
• Control Permeability- regulates molecules that enter or leave through the surface.
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Permeability Can Change!
CornCallus
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Functions of Epithelia
• Provides Sensation- many sensory nerves; Ex: smell, taste, hearing.
• Produce Specialized Secretions- gland cells produce secretions
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Some Characteristics• Cellularity: tightly bound cells with little
space between.
• Polarity: has an exposed surface- apical surface (faces exterior surface ) and an attached surface-basal surface (attached to underlying tissue). Organelles are distributed unevenly in these cell.
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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.
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Characteristics
• Regeneration: cells damaged or lost at the apical surface are replaced constantly.
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How do epithelial cells do ALL of this?
The answer is in their structure!
Function Structure
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Specialized Epithelial CellsSome 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).
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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.
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Microvilli
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Apical Surface Structures2. 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)
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Cilia
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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.
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StereociliaStereocilia
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Show me Ciliated Epithelia in Action!
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Damaged Epithelia and Emphysema
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The Effects of Emphysema
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Staying Together!3 Ways Epithelial Cells Stay
Together:1. Intercellular Connections2. Attachment to Basal Membrane3. Epithelial Maintenance and Repair
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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.
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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.
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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 cells-coordinate functions-beating cilia.Found: lateral; cardiac and smooth muscle
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Connexons or Channel Proteins
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2. Basement Membrane
• A layer of protein fibers to which epithelia can attach.
• Separates epithelial layer from connective tissue.
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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.
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QuickTime™ and aGIF decompressor
are needed to see this picture.
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How many kinds of epithelia are there?
Classified in Two Ways:
Number of Layers and Shape of Cell
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A. Layers1. 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.
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A. Layers2. 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.
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B. Shape1. Squamous- “scale” thin, flat cells; look
like fried eggs laid side by side.
Ex. Simple Squamous Epithelium- walls 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.
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Simple Squamous Epithelium
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Apical View of Simple Squamous
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Simple Squamous: Cross-Sectional View of Blood Vessel
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Simple Squamous: Cross-Sectional View of Lung Alveoli
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Stratified Squamous Epithelium
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Stratified Squamous - Cheek Cells
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Stratified Squamous
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Stratified Squamous-Cross Section, Lower Magnification
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Stratified Squamous-Cross Section, Higher Magnification
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B. Shape2. 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.
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Simple Cuboidal Epithelium
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Simple Cuboidal: X-Section of Kidney Tubules
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Transitional Epithelium: Ureter, Lower Magnification
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Transitional Epithelium: Ureter, Higher Magnification
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B. Shape3. 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.
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Simple Columnar Epithelium
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B. Shape3. Columnar-Ex. Pseudostratified Columnar- nuclei
not in same plane- appear stratified, but not. All cells contact the B.M. Found- respiratory tract- have cilia; line trachea, nasal cavity.
Stratified Columnar- rare; protective; line epiglottis and pharynx
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Simple Columnar: Small Intestine (Villi)
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Simple Pseudostratified
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Pseudostratified Epithelium
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Pseudostratified Ciliated Columnar
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Stratified Columnar
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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)
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Glandular Epithelia
• Exocrine Glands- secretions discharged onto epithelial surfaces; released into tubular passageways-ducts that empty onto surface of other epithelial tissues.
• Examples- sweat, saliva, and tears.
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QuickTime™ and aGIF decompressor
are needed to see this picture.
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Lets’ see epithelia in action!
National Geographic magazine, November 2002
National Geographic video Skin, November 13, 2002