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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! Corn Callus
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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 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).
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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 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)
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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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Stereocilia
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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 Connections 2. Attachment to Basal Membrane 3. 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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The Layers of Skin
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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. 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.
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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.
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B. Shape 1.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. 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.
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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. 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.
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Simple Columnar Epithelium
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B. Shape 3. 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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Lets’ see epithelia in action! National Geographic magazine, November 2002 National Geographic video Skin, November 13, 2002
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