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CHAPTER 4
Tissues
1
INTRODUCTION
• Tissue = group of similar cells w/ similar origin & function
• Characteristics of extracellular material surrounding cells
of a tissue influence structure & properties of that tissue
• Histology
– study of tissues
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TYPES OF TISSUES
Four principal types based on function and structure:
1) Epithelial tissue
– Covers body surfaces
– Lines hollow organs, body cavities, & ducts
– Forms glands
2) Connective tissue
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Protects & supports body and its organs
Binds organs together
Stores energy reserves as fat
Provides immunity
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TYPES OF TISSUES
3) Muscle tissue
– Responsible for movement and generation of force
4) Nervous tissue
– Detects changes in internal/external environments
– Initiates & transmits nerve impulses to coordinate
body activities
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CELL JUNCTIONS
• Points of contact between adjacent plasma
membranes (usually btwn epithelial cells)
• One of three functions, depending on structure
– Form fluid-tight seals between cells
– Anchor cells together or to extracellular material
– Act as channels which allow ions and molecules to
pass from cell to cell within a tissue
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Tight Junctions
• Trans-membrane
proteins fuse outer
surfaces of PM of
neighboring cells
• Slow passage of
substances between cells
• Watertight seal 
prevent leakage
• Found btwn epithelial
cells that line GI and
bladder
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Adherens Junctions
• Prevents separation of
epithelial cells during
contractile activity
• Plaque
– Attaches to PM &
microfilaments in
cytoskeleton
– Cadherins join cells
• Adhesion belts = zones of
adherens junctions
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Gap Junctions
• Connect neighboring cells
• Connexons
– Ions & small molecules can
diffuse
– Nutrient transfer in
avascular tissues  Ex:
cornea, lens
• Cell communication
– Signal transmission
• Muscle and nerve impulses
spread from cell to cell
– Heart; smooth muscle in GI
tract & uterus
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Desmosomes
• Plaque & glycoprotien
extend into intercellular
space btwn adjacent PM
– intermediate filaments
extend across cytoplasm
• “Spot-weld” resists
cellular separation &
disruption
– EX: Cellular support of
cardiac muscle &
epidermis
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Hemidesmosomes
• Do not link adjacent cells
• Anchor cells to basement
membrane
• Integrins in XC space
– Attach to keratin inside
– Attach to laminin (in
basement membrane)
outside cell
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EPITHELIAL TISSUE
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•
•
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Cells arranged in continuous sheets
Single or multiple layers
Little intercellular space
Apical (free) surface faces body surface, cavity or lumen
of internal organ
– May contain cilia or microvilli
• Lateral surface faces adjacent cells
• Basal surface adheres to XC material (basement
membrane)
– Anchored to basement membrane by hemisdesmosomes
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Epithelial Tissue
• Avascular
– nutrients and waste must move by diffusion
• Good nerve supply
• Rapid cell division (high mitotic rate)
• Functions
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Protection
Filtration
Lubrication
Secretion/Absorption
Many other functions…
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Basement Membrane
• Thin extracellular layer that serves as point of
attachment for overlying ET
• Two layers:
– Basal lamina
• Closer to & secreted by epithelium
• Collagen, glycoprotein, laminin
• Laminin adheres to integrin in hemidesmosomes  anchor
– Reticular lamina
• Closer to connective tissue
• Contains fibrous proteins
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Types of Epithelium
• Covering and lining epithelium
– epidermis of skin
– lining of blood vessels and ducts
– lining of respiratory, reproductive, urinary & GI tracts
• Glandular epithelium
– secreting portion of glands
– thyroid, adrenal, and sweat glands
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Classification of Epithelium
• Classified by arrangement of cells into layers
– Simple = one cell layer thick
• functions: diffusion, osmosis, filtration,
secretion/absorption
– Stratified = two or more cell layers thick
• classified by shape of cells at apical surface
• protects underlying tissue where considerable wear &
tear
– Pseudostratified = appears to have multiple layers
• cells contact BM but not all extend to apical surface
• nuclei are located at multiple levels so it looks
multilayered
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Classification of Epithelium
• Classified by shape of surface cells (Table 4.1)
– Squamous = flat
• Thin, arranged like floor tiles
• Allow for rapid passage of substances
– Cuboidal = cube-shaped
• May have microvilli @ apical surface
• Function in secretion or absorption
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Classification of Epithelium
– Columnar = tall & narrow
• Protect underlying surfaces
• Secretion or absorption
• May have cilia or microvilli
– Transitional = shape varies with tissue stretching
• Urinary bladder
• Change from flat to cuboidal with stretching
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Simple Squamous Epithelium
• Single layer of thin, flat cells
– Controls diffusion, osmosis and filtration
• heart & blood vessel lining (endothelium)
• lining of body cavities (mesothelium)
Simple Cuboidal Epithelium
• Single layer of cube-shaped cells
– nuclei are round and centrally located
– lines tubes of kidney, lines GI structures
– adapted for absorption or secretion
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Nonciliated Simple Columnar
• Single layer rectangular cells
• Unicellular glands (goblet cells) secrete mucus
– lubricate GI, respiratory, reproductive and urinary systems
• Adapted for absorption in GI tract
– Microvilli increase surface area & rate of absorption
Ciliated Simple Columnar Epithelium
• Single layer columnar cells with cilia @ apical surface
• Contain goblet cells in some locations
– secrete mucus
• Cilia move mucus & other substances along a surface
– found in respiratory system and in uterine tubes
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Pseudostratified Columnar Epithelium
• Single layer of cells of variable height
• All cells anchored to basement membrane
• Some cells reach apical surface:
– secrete mucus (goblet cells)
– cilia sweep away mucus & trapped foreign particles
• Found in respiratory system, male urethra & epididymis
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Stratified Epithelium
• Protective, durable
• Keratinized stratified squamous epithelium
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–
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epidermis (outer layer of skin)
layer of keratin deposited in (dead) apical cells
deeper layers of cells vary cuboidal to columnar
basal cells replicate by mitosis
• Nonkeratinized stratified squamous epithelium
– lines wet surfaces
• Stratified cuboidal & stratified columnar
– uncommon types of epithelia
– primarily function in protection
– limited secretion functions
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Transitional Epithelium
• Several layers of various shapes
– Vary from round to flat (if stretched)
– Permits distention of an organ
– Lines hollow organs that expand from within
• Urinary bladder
• Portions of ureters & urethra
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Glandular Epithelium
• Functions in secretion
• Single-celled or multi-celled glands
• Endocrine glands
– Ductless
– Secrete products directly into bloodstream
– Ex: hormone secretion
• Exocrine glands secrete products into ducts
– Empty @ surface of covering/lining epithelium
– Empty directly onto a free surface
– EX: sweat, oil, earwax & digestive enzymes
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Structural Classification of Exocrine Glands
• Unicellular glands
– Goblet cells
• secrete mucus onto apical surface of lining epithelium
• Multicellular glands
– Sweat, sebaceous, salivary glands
– Categorized by shape & branching
• tubular, acinar or tubuloacinar
– shape of secretory portion
• simple vs. compound
– duct is not branched vs. branched
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Functional Classification of Exocrine Glands
• Merocrine glands
– secretory products formed in RER & packaged by Golgi
– products discharged by exocytosis
• Apocrine glands
– secretory products accumulate @ apical surface of cell
– portion pinches off from rest of cell to form the secretion
– remainder of cell repairs itself
• Holocrine glands
– accumulate secretory product in cytosol
– cell matures, ruptures & becomes secretory product
– discharged cell replaced by new one
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CONNECTIVE TISSUE
• Binds, supports & strengthens other tissues
• Protects & insulates internal organs
• Compartmentalizes structures (skeletal muscle)
• Major transport system (blood)
• Stored energy reserve (adipose)
• Derived from **mesenchyme**
– Immature cells in “–blast” (e.g., fibroblast, chondroblast)
– Mature cells end in “-cyte” (e.g., osteocyte)
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Connective Tissues
• 2 basic elements
– Cells
– Extracellular matrix (ECM)
• Fibers & ground substance secreted by cells
• **Nature of ECM determines tissue characteristics
– liquid, gel or solid
• Highly vascularized except in cartilage & tendons
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Connective Tissue Cells
• ‘-blast’ cells retain mitotic capacity & secrete ECM
• Vary according to tissue type
• Fibroblasts
– Migrate thru C.T. & secrete fibers & ground substance
– Usually most numerous cell in C.T.
– Large, flat with branched processes
• Macrophages
– Derived from WBC
– Engulf bacteria & debris by phagocytosis
– Fixed or wandering
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Connective Tissue Cells
• Adipocytes
– Store energy (as triglycerides)
– Insulate organs
• Plasma cells
– Derived from B lymphocytes
– Secrete antibodies  immune response
– Reside in C.T. in GI & respir. tracts
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Connective Tissue Cells
• Mast cells
– Produce histamines  dilate blood vessels as part of
inflammatory response
– Abundant in blood vessels that supply C.T.
– Can phagocytize bacteria
• White blood cells (WBC)
– Few found in normal C. T.
– Migrate from blood into C.T. in response to certain “foreign”
conditions
– Neutrophils, eosinophils
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Extracellular Matrix: Ground Substance
• Ground Substance
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Gives C.T. its characteristic properties
Found between CT cells and fibers
Fluid, semi-fluid, gelatinous or calcified
Supports & binds cells
Nutrient exchange between blood & cells
Contains polysaccharides
• glycosaminoglycans (GAG’s) trap water  jellylike substance
– hyaluronic acid = thick, viscous and slippery lubrication
– chondroitin sulfate  support in bone, skin, blood vessels
– Fibronectin = main adhesion protein in CT
• Chondroitin sulfate and glucosamine are used as
nutritional supplements to maintain joint cartilage.
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Extracellular Matrix: Fibers
• Collagen fibers
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Composed of collagen protein
Properties differ with tissue type
Tough & resistant to stretching
Allow some flexibility in tissue
Found in most types of C.T.
• Bone
• Cartilage
• Tendons
• Ligaments
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Extracellular Matrix: Fibers
• Elastic fibers
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Branched network within tissue
Made of elastin (protein) + fibrillin (glycoprotein)
Can be stretched up to 150% of length
Ability to return to original shape after being stretched
Provide strength
Plentiful in regions where stretch occurs
• skin, blood vessels, and lungs
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Extracellular Matrix: Fibers
• Reticular fibers
– Collagen coated with glycoprotein
– Support in walls of blood vessels, in spleen, in lymph nodes
– Form supporting network around cells in some tissues
• Nerve fibers
• Skeletal & smooth muscle fibers
– Produced by fibroblasts
– Plentiful in reticular C. T.
• Forms stroma (supporting network) for soft organs
– Spleen, lymph nodes
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Embryonic Connective Tissue
• Mesenchyme
– Origin of all C.T.
– semifluid ground substance + reticular fibers
– found almost exclusively in embryo
• Mucous connective tissue (Wharton’s jelly)
– Found mainly in umbilical cord of fetus
– Scattered fibroblasts, viscous ground substance & collagen
fibers
– Supports other tissues
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Types of Mature Connective Tissue
1) Loose connective tissue
– Areolar, adipose, reticular
2) Dense connective tissue
– Dense regular, dense irregular, elastic
3) Cartilage
– Hyaline, elastic, fibrocartilage
4) Bone tissue
– Compact & trabecular
5) Liquid connective tissue
– Plasma & lymph
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Loose CT
• Areolar
– Random arrgmt of all 3 fiber types
– Contains numerous cell types
– Combined w/ adipose, forms subcutaneous layer
• Reticular
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Lots of finely interlaced reticular fibers & cells
Filters blood lymph—removes old cells & bacteria
Supporting framework for liver, spleen, lymph nodes
Binds smooth muscle cells
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Loose CT: Adipose
• Cells (adipocytes) specialized for fat storage
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Found wherever areolar connective tissue is located
Cytoplasm & nucleus pushed to cell periphery
Reduces heat loss through the skin
Supports, protects, insulates organs
Brown adipose generates heat to maintain body
temperature in newborns
– White adipose = adipose tissue found in adults
• Liposuction involves sucking out small amounts of
adipose tissue.
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Dense CT
• Dense regular
– Bundles of collagen fibers regularly arranged in parallel
patterns
– Tough but pliable
– Withstands pulling along axis of fiber
– Ex: tendons & ligaments
• Dense irregular
– Collagen fibers irregularly arranged (interwoven)
– Provides strength to resist pulling in various directions
– Ex: dermis, pericardium
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Dense CT
• Elastic CT
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Branching elastic fibers
Fibroblasts between fibers
Very strong  can stretch & recoil to original shape
Ex: lung tissue, vocal cords, ligament between vertebrae
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Cartilage
• Dense network of collagen & elastic fibers embedded in
chondroitin sulfate
– collagen fibers  strength
– chondroitin sulfate  resilience
• Can endure more stress than loose & dense C.T.’s
• Mature cells = chondrocytes  found in lacunae in ECM
• Covered by a dense irregular CT membrane called
perichondrium
• Avascular except @ perichondrium
• 3 subtypes
• Growth
– Interstitial (from within)
– Appositional (from the outside)
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Hyaline Cartilage
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Resilient gel ground substance
Most abundant, but weakest cartilage
Provides flexibility & support
Reduces friction & absorbs shock at joints
No blood vessels or nerves so repair is very slow
Fibrocartilage
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Strongest cartilage (intervertebral discs)
Chondrocytes scattered among bundles of collagen fibers
No perichondrium
Collagen fibers causes rigidity & stiffness
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Elastic Cartilage
• Threadlike network of elastic fibers
• Strength and elasticity
• Elastic fibers maintain shape after deformations
• Ex: ear, nose, vocal cartilages
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Growth & Repair of Cartilage
• Slow because tissue is avascular
• Interstitial growth
– Occurs from within
– Rapid increase in size
• Chondrocytes divide
• Increased deposition of new matrix
– Occurs in childhood and adolescence
• Appositional growth
– Activity of inner layer of perichondrium
• Chondroblasts secrete matrix onto surface
• ECM accumulates beneath
– Produces increase in width
– Continues thru adolescence
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Bone Tissue
• Protection, support, mineral storage
• Provides for movement
• Calcified matrix contains mineral salts, collagenous
fibers & cells called osteocytes
– Compact bone
• solid, dense bone
• basic unit of structure is osteon (haversian system)
– Spongy bone
• sponge-like with spaces and trabeculae
• trabeculae = struts of bone surrounded by red bone
marrow
• no osteons (cellular organization)
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Liquid connective tissue
• Blood
– liquid matrix called plasma
– formed elements (Table 4.4K)
• Lymph is interstitial fluid flowing in lymph vessels.
– Contains less protein than plasma
– Move cells and substances (eg., lipids) from one part of the
body to another
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MEMBRANES
• Flat sheets of pliable tissue that cover or line body parts
• Epithelial membranes have epithelial layer &
underlying connective tissue layer (lamina propria)
– mucous membranes
– serous membranes
– cutaneous membrane (skin)
• Synovial membranes line joints & contain only
connective tissue
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Mucous Membranes
• Line cavities that open to exterior
– Digestive tract
– Reproductive tract
• Epithelial layer
– Defense mechanism
– Secretes enzymes
– Cells vary from body part to body part
• Connective tissue layer = lamina propria
– Supports epithelium & binds to underlying structures
• Tight junctions prevent simple diffusion of most
substances
• Mucus secreted from underlying goblet cells to keep
surface moist
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Serous Membranes
• Lines cavities not open to exterior
– Covers organs within cavity
– Ex: abdominal cavity
• Mesothelium covers areolar C.T. layer
– simple squamous cells
– secretes serous fluid
• 2 layers
• parietal layer lines walls of cavity
• visceral layer covers organs in cavity
• Serous membranes may become inflamed with the
buildup of serous fluid resulting in pleurisy, peritonitis, or
pericarditis
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Cutaneous Membrane
• Cutaneous membranes (skin)
• Cover body surfaces
• Epidermis (superficial)
– Keratinized stratified squamous epithelium
• Dermis (deep)
– Areolar connective tissue
– Dense irregular connective tissue
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Synovial Membranes
• Line cavities of freely movable joints
• Line structures not open to exterior  bursae & tendon
sheaths
• Discontinuous layer of synoviocytes only  No epithelial
cells
– Secrete slippery synovial fluid
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EXCITABLE CELLS
• Neurons and muscle fibers are excitable cells
– Ability to produce action potentials
• Action potentials propagate along plasma membrane
due to voltage-gated channels
– In neurons  release of neurotransmitter
– In muscle cells  muscle contraction
• Action potentials will be discussed further in Chapters
10 and 12.
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