TISSUES

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TISSUES
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STRUCTURAL ORGANIZATION

• Life is characterized by hierarchical orders of
  organization
• Atoms
• Molecules
• Organelles
• Cells
• Tissues
• Organs
• Organ systems
• Organism
• (Population)
• (Community)
• (Ecosystem)

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STRUCTURAL ORGANIZATION

• The cell is the lowest level of organization that
  can live independently as an organism

Amoeba
Paramecium
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STRUCTURAL ORGANIZATION

• In multicellular organisms, specialized cells are
  grouped into tissues
• A tissue is a group of cells similar in structure
  and performing a common function
• Organs are comprised of combinations of various
  tissues
• Organ systems include multiple organs working
  together

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INTERCELLULAR JUNCTIONS

• Neighboring cells within a multicellular organism
  often adhere, interact, and communicate through
  intracellular junctions
• Tight junctions
• Desmosomes
• Gap junctions

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TIGHT JUNCTIONS

• Integral membrane proteins of adjacent cells fuse
  together
• Membranes of adjacent cells are fused
• Form continuous belts around cells
• Impermeable barrier
• Some tight junctions are somewhat leaky
• Not-so-tight junctions

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DESMOSOMES

• Anchoring junctions
• Rivets keeping adjacent cells from separating
• Composition
• Button-like plaque on cytoplasmic face of
  membrane
• Thin linker protein filaments interdigitate
• Desmosomes on opposite sides of the same cell
  connected through intermediate filaments

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GAP JUNCTIONS

• Communicating junction connecting cytoplasm of
  adjacent cells
• Composition
• Transmembrane proteins form connexons
• Hollow tubes
• Connexons of adjacent cells fuse
• Chemical substances travel through these
  channels
• Different connexons have different specificities

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TISSUE TYPES

• Four major tissue types
• Epithelial tissue
• Connective tissue
• Muscle tissue
• Nervous tissue

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EPITHELIAL TISSUE

• Sheets of cells covering body surfaces or lining
  body cavities
• Form boundaries between different environments
• e.g., Epidermis of skin separates inside and
  outside of body
• e.g., Epithelium lining urinary bladder separates
  underlying cells from urine

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EPITHELIAL TISSUE

• Many diverse functions
• Protection
• Absorption
• Filtration
• Excretion
• Secretion
• Sensory reception

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EPITHELIUM CHARACTERISTICS

• Cellularity
• Little extracellular material
• Specialized contacts
• Tight junctions desmosomes
• Polarity
• Basal and apical surfaces
• Supported by connective tissue
• Avascular
• Nourished from below
• Innervated
• Regeneration
• Rapid cell division at basal surface

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CLASSIFICATION OF EPITHELIA

• Cell layers
• Simple epithelia
• Single cell layer
• Facilitates absorption and filtration
• Stratified epithelia
• Two or more cell layers
• Common in high-abrasion areas
• e.g., Skin surface, mouth

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CLASSIFICATION OF EPITHELIA

• Cell shape
• All epithelia have six sides
• Cells vary in height
• Three common shapes
• Squamous cells
• Cuboidal cells
• Columnar cells
• Shape of nucleus conforms to shape of cell

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CLASSIFICATION OF EPITHELIA

• Cell layers cell shape
• Two names
• First name indicates cell layers
• Second name indicates cell shape
• e.g., Simple squamous epithelium
• e.g., Stratified cuboidal epithelium

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SIMPLE SQUAMOUS EPITHELIUM

• Flattened
• Sparse cytoplasm
• Resemble tiled floor from top
• Resemble fried egg from side
• Thin and permeable
• Found where exchange is important
• e.g., Filtration in kidneys
• e.g., Rapid diffusion in lungs, capillaries

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SIMPLE SQUAMOUS EPITHELIUM

• Two have special names reflecting their location
• Endothelium
• Inner lining of the heart, blood vessels, and
  lymphatic vessels
• Capillaries are exclusively endothelium
• Mesothelium
• Found in serous membranes lining the ventral body
  cavity and covering its organs

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SIMPLE CUBOIDAL EPITHELIUM

• Forms the walls of the smallest ducts of glands
  and of many kidney tubules

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SIMPLE COLUMNAR EPITHELIUM

• Mainly associated with absorption secretion
• Lines digestive tract (stomach ? rectum)
• Microvilli on apical surface of absorptive cells
• Mucus-secreting goblet cells
• May possess cilia

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PSEUDOSTRATIFIED COLUMNAR EPITHELIUM

• Single layer of cells
• All cells rest on basement membrane
• Cells vary in height
• Only tallest cells reach free (apical) surface
• Gives false appearance of multiple layers
• Secretes or absorbs substances
• May possess cilia
• May possess goblet cells

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STRATIFIED EPITHELIA

• Possess two or more cell layers
• Regenerate from below
• Basal cells divide and push apically (upward)
• More durable than simple epithelia
• Protection is major role

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STRATIFIED SQUAMOUS EPITHELIUM

• Most widespread of stratified epithelia
• Found in areas subjected to wear and tear
• External part of skin, extending into body
  openings directly continuous with skin
• Free surface cells are squamous
• Cells in deeper layers are cuboidal or columnar

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STRATIFIED SQUAMOUS EPITHELIUM

• Free surface (apical) cells less viable
• Avascular ? fewer nutrients further from blood
• Outer layer of skin is keratinized
• Cells filled with resinous protein keratin
• Protective role

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STRATIFIED CUBOIDAL OR COLUMNAR EPITHELIUM

• Both are rather rare in the body
• Cuboidal
• Present in ducts of some larger glands
• e.g., Sweat glands, mammary glands
• Typically two layers of cuboidal cells
• Columnar
• Only apical layer is columnar
• Limited distribution
• e.g., Pharynx, ? urethra, line some glandular
  ducts
• Also present at transition areas or junctions
  between two other types of epithelia

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TRANSITIONAL EPITHELIUM

• Forms lining of hollow urinary organs
• Bladder and ureters
• Basal layer cuboidal or columnar
• Apical cells vary in appearance
• Appearance depends on degree of distension
• 6 cell layers when empty
• Thins to 3 layers when distended with urine
• Allows more urine to be stored or transported

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GLANDULAR EPITHELIA

• A gland consists of one or more cells that
  produce and secrete a product (secretion)
• Secretion verb and noun
• Endocrine vs. exocrine
• Unicellular vs. multicellular

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ENDOCRINE GLANDS

• Ductless glands
• (Ducts are eventually lost)
• Produce hormones
• Secreted directly into extracellular space via
  exocytosis
• Many (but not all) are epithelial derivatives
• More information in their own chapter

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EXOCRINE GLANDS

• More numerous than endocrine glands
• Secrete into body cavities or onto body surfaces
• (i.e., Not into extracellular space)
• Unicellular glands via exocytosis
• Multicellular glands via ducts
• Diverse
• e.g., Mucous, sweat, oil, and salivary glands,
  etc.

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EXOCRINE GLANDS

• Unicellular Gland Goblet cell
• Shaped like a goblet
• Present in columnar epithelia of intestinal and
  respiratory tracts
• Produce mucin
• Mucin water ? mucus
• Protects and lubricates

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EXOCRINE GLANDS

• Multicellular Glands
• Structurally more complex
• Two parts
• Epithelium-derived duct
• Secretory unit
• Surrounded by connective tissue
• Supplies blood vessels and nerves
• Capsule divides gland into lobes

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EXOCRINE GLANDS

• Multicellular Glands Structural Classification
• Simple
• Compound
• Tubular
• Alveolar (acinar)
• Tubuloalveolar

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EXOCRINE GLANDS

• Multicellular Glands Mode of Secretion
• Merocrine glands
• Most common
• Secrete products by exocytosis
• e.g., Pancreas, sweat salivary glands
• Holocrine glands
• Accumulate products within, then rupture
• Replaced by division of underlying cells
• e.g., Sebaceous (oil) glands
• Apocrine glands
• Present in other animals, maybe in humans
• Accumulate beneath surface, pinch off
• e.g., Lipid droplets from mammary glands

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CONNECTIVE TISSUE

• Found everywhere in the body
• Most widely distributed primary tissue
• Four main classes
• Connective tissue proper
• Cartilage
• Bone tissue
• Blood

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CONNECTIVE TISSUE

• Major functions
• Binding and support
• Protection
• Insulation
• Transportation
• Which of these functions are accomplished by bone
  and cartilage? Fat? Blood?

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CONNECTIVE TISSUE

• Common Characteristics
• Common origin
• All connective tissues arise from mesenchyme
  (an embryonic tissue)
• Degrees of vascularity
• Avascular
• poorly vascular
• highly vascular
• Extracellular matrix
• Largely composed of non-living extracellular
  matrix

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CONNECTIVE TISSUE

• Three main structural elements
• Ground substance
• Fibers
• Cells
• Ground substance fibers matrix

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GROUND SUBSTANCE

• Unstructured material filling space between cells
• Contains fibers
• Composed of
• Interstitial (tissue) fluid
• Cell adhesion proteins
• Glue attaching cells to matrix elements
• Proteoglycans
• Glycosaminoglycans (GAGs) attached to a protein
  core
• Large, negatively charged polysaccharides
• e.g., Hyaluronic acid, etc.
• Traps H2O
• Holds fluid ? facilitates diffusion of dissolved
  substances between blood capillaries and cells

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FIBERS

• Three types of fibers provide support
• Collagen fibers
• White fibers
• Strongest and most abundant
• Tensile strength steel
• Elastic fibers
• Yellow fibers
• Long, thin, branching fibers
• Contain the protein elastin
• Can stretch and recoil
• Reticular fibers
• Fine collagenous fibers
• Networks surround and support soft tissue of
  organs

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CELLS

• Each major class of connective tissue is derived
  from a fundamental cell type (_____-blast)
• Fibroblast ? connective tissue proper
• Hematopoietic stem cell ? blood
• Chondroblast ? cartilage
• Osteoblast ? bone
• ___-blasts ultimately derived from mesenchyme

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CELLS

• Each major class of connective tissue is derived
  from a fundamental cell type (_____-blast)
• Fibroblast ? connective tissue proper
• Hematopoietic stem cell ? blood
• Chondroblast ? cartilage
• Osteoblast ? bone
• Assume mature form (___-cyte) after matrix is
  made
• Less active
• Maintain health of matrix
• Revert to blast form to repair and regenerate
  matrix

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CELLS

• Connective tissue is a home for many other cell
  types
• Fat cells
• Leukocytes
• Macrophages
• Mast cells
• These last three types of cells will be dealt
  with in great detail in the blood chapter
• Macrophages and mast cells will be dealt with in
  some detail now

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CELLS

• Mast cells
• Cluster along blood vessels
• Detect foreign substances
• e.g., microorganisms
• Release secretory granules to initiate local
  inflammatory response
• Macrophages
• Descended from monocytes
• Relatively large phagocytic cells
• Eat foreign material
• Mobile or fixed

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TYPES OF CONNECTIVE TISSUE

• Embryonic Connective Tissue Mesenchyme
• Star-shaped mesenchymal cells
• Fluid ground substance
• Arises early in embryonic development
• Differentiates into all other connective tissues

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TYPES OF CONNECTIVE TISSUE

• Connective Tissue Proper
• Two subclasses
• Loose connective tissue
• Areolar
• Adipose
• Reticular
• Dense connective tissue
• Dense regular
• Dense irregular
• Elastic

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TYPES OF CONNECTIVE TISSUE

• Loose Connective Tissue Areolar
• Functions
• Supporting and binding other tissues
• Fibers
• Holding body fluids
• Ground substance
• Defending against infection
• Leukocytes
• Macrophages
• Storing nutrients
• Fat cells

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TYPES OF CONNECTIVE TISSUE

• Loose Connective Tissue Areolar
• Most widely distributed connective tissue
• Functions
• Supporting and binding other tissues
• Fibers
• Holding body fluids
• Ground substance
• Defending against infection
• Leukocytes
• Macrophages
• Storing nutrients
• Fat cells

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TYPES OF CONNECTIVE TISSUE

• Loose Connective Tissue Areolar
• Loose arrangement of fibers
• Remainder of matrix appears to be empty space
• Occupied by ground substance
• Provides reservoir of salts and water for
  surrounding body tissues
• Holds amount of fluid equivalent to blood volume
• Most body cells obtain nutrients and release
  wastes into this tissue fluid
• Inflammation ? edema

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TYPES OF CONNECTIVE TISSUE

• Loose Connective Tissue Areolar
• Ground substance rich in hyaluronic acid
• Makes ground substance viscous
• Can impede microbes
• Can also impede movement of cells
• Some leukocytes secrete hyaluronidase
• Enzyme liquefying hyaluronic acid
• Some bacteria also produce this enzyme

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TYPES OF CONNECTIVE TISSUE

• Loose Connective Tissue Areolar
• Fibroblasts predominate
• Numerous macrophages
• Fat cells singly or in small clusters
• Occasional mast cells
• Other cell types also sparsely present

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TYPES OF CONNECTIVE TISSUE

• Loose Connective Tissue Adipose (Fat) Tissue
• Similar to areolar tissue in structure and
  function
• Greater nutrient-storing ability
• Adipocytes predominate
• Adipose cells / fat cells
• 90 of tissues mass
• Among bodys largest cells
• Cells packed tight
• Scanty matrix
• Oil droplet occupies most of cell volume
• Nucleus and thin crescent of cytoplasm visible on
  periphery

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TYPES OF CONNECTIVE TISSUE

• Loose Connective Tissue Adipose (Fat) Tissue
• Richly vascularized
• High metabolic activity
• 18 of average persons body mass
• Insulates absorbs shocks
• May develop almost anywhere
• e.g., Subcutaneous tissue
• e.g., Surrounding kidneys

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TYPES OF CONNECTIVE TISSUE

• Loose Connective Tissue Adipose (Fat) Tissue
• Subcutaneous fat serves energy needs of the body
  as a whole
• Smaller fat deposits serve local nutrient needs
  of highly active organs
• e.g., Heart, lymph nodes, muscles, etc.

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TYPES OF CONNECTIVE TISSUE

• Loose Connective Tissue Adipose (Fat) Tissue
• White fat has just been described
• Brown fat is a variant found only in infants
• Found between shoulder blades, anterior abdominal
  wall, and anterolateral neck
• Nutrient stores consumed to generate heat
• Babies are not yet able to shiver to generate heat

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TYPES OF CONNECTIVE TISSUE

• Loose Connective Tissue Reticular
• Present in lymph nodes, spleen, bone marrow
• Resembles areolar tissue
• Only fibers present are reticular fibers
• Forms framework supporting many free blood
  cells
• e.g., Lymphocytes

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TYPES OF CONNECTIVE TISSUE

• Dense Regular Connective Tissue
• Fibers are predominant element
• a.k.a. Fibrous connective tissues
• Contain closely packed bundles of collagen fibers
• Run together, parallel to direction of pull
• Great resistance to tension exerted in a single
  direction

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TYPES OF CONNECTIVE TISSUE

• Dense Regular Connective Tissue
• Rows of fibroblasts manufacture fibers and scant
  ground substance
• Very few cells of other types
• Poorly vascularized

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TYPES OF CONNECTIVE TISSUE

• Dense Regular Connective Tissue
• Forms tendons
• Attach muscles to bones or muscles
• Forms ligaments
• Bind bones together at joints
• More elastic fibers than tendons
• What feature of dense regular connective tissue
  is responsible for their slow rate of healing?

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TYPES OF CONNECTIVE TISSUE

• Dense Regular Connective Tissue
• Most is dense regular collagenous
• Some is dense regular elastic
• Contains abundant elastic fibers
• Forms some elastic ligaments
• e.g., Nuchal ligament along posterior of neck,
  ligaments between vertebrae, vocal cords

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TYPES OF CONNECTIVE TISSUE

• Dense Irregular Collagenous Connective Tissue
• Same structural elements as dense regular
• Bundles of collagen fibers
• Thicker
• Arranged irregularly (run in 1 plane)
• Withstands tension from many directions
• Found in dermis of skin fibrous joint capsules,
  fibrous coverings of some organs (e.g., testes,
  kidneys, etc.)

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TYPES OF CONNECTIVE TISSUE

• Dense Irregular Elastic Connective Tissue
• Similar to dense irregular collagenous
• Contains abundant elastic fibers
• Found in wall of elastic arteries

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TYPES OF CONNECTIVE TISSUE

• Cartilage
• Tough and flexible
• Withstands both tension and compression
• Intermediate between dense connective tissue and
  bone
• Lacks nerve fibers
• Avascular
• Ground substance rich in GAGs
• Large amount of tissue fluid
• Up to 80 water
• Chondroblasts are predominant cell type
• Produce new matrix

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TYPES OF CONNECTIVE TISSUE

• Cartilage
• Three varieties
• Hyaline cartilage
• Elastic cartilage
• Fibrocartilage

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TYPES OF CONNECTIVE TISSUE

• Hyaline Cartilage
• Most abundant type of cartilage
• Covers ends of long bones
• Articular cartilage
• Forms epiphyseal plate
• Allows growth in long bones
• Supports tip of nose, connects ribs to sternum,
  supports respiratory system passages
• Large numbers of collagen fibers
• Not apparent in matrix
• Chondrocytes only 1 10 of volume

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TYPES OF CONNECTIVE TISSUE

• Elastic Cartilage
• Nearly identical to hyaline cartilage
• Many more elastin fibers
• Supports external ear, epiglottis

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TYPES OF CONNECTIVE TISSUE

• Fibrocartilage
• Structural intermediate between hyaline cartilage
  and dense regular connective tissue
• Rows of chondrocytes alternate with rows of thick
  collagen fibers
• Compressible, resists tension
• Often found where hyaline cartilage meets a
  true tendon or ligament
• Intervertebral disks, spongy cartilages of the
  knee

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TYPES OF CONNECTIVE TISSUE

• Bone (Osseous Tissue)
• Matrix similar to cartilage
• More abundant collagen fibers
• Inorganic calcium salts
• Rocklike hardness
• Ability to support protect

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TYPES OF CONNECTIVE TISSUE

• Bone (Osseous Tissue)
• Osteoblasts produce organic portion of matrix
• Bone salts then deposited on between fibers
• Osteoblasts ? osteocytes
• Osteocytes reside in lacunae within the matrix
• Vascular

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TYPES OF CONNECTIVE TISSUE

• Blood
• Very atypical connective tissue
• Does NOT connect things
• Provides NO mechanical support
• Why is it considered connective tissue?
• Derived from mesenchyme

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TYPES OF CONNECTIVE TISSUE

• Blood
• Various types of cells
• Blood plasma is fluid matrix
• Plasma proteins are fibers
• Various functions
• Transportation
• Protection

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MEMBRANES

• Continuous multiple sheets comprised of
• Epithelium
• Underlying layer of connective tissue
• Three types of covering and lining membranes
• Cutaneous
• Mucous
• Serous
• These membranes are multicellular structures,
  and are quite different from the plasma membrane
  of a cell

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CUTANEOUS MEMBRANES

• a.k.a., Skin
• Organ system
• Consists of
• Keratinized stratified squamous epithelium
• Epidermis
• Thick layer of dense irregular connective tissue
• Dermis
• Dry membrane

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MUCOUS MEMBRANES

• a.k.a., Mucosae
• Line body cavities open to exterior
• e.g., digestive, respiratory, urogenital tracts
• Wet membranes
• Bathed in secretions or urine
• Often adapted for absorption and secretion
• Many secrete mucus
• Not all (urinary)

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MUCOUS MEMBRANES

• Most mucosae contain either stratified squamous
  or simple columnar epithelia
• Underlain by a layer of loose connective tissue
• Lamina propria
• Lamina propria may rest on deeper layer of smooth
  muscle

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SEROUS MEMBRANES

• a.k.a., Serosae
• Moist membranes found in closed ventral body
  cavities
• Consist of
• Simple squamous epithelium (mesothelium)
• Thin layer of loose connective (areolar) tissue
• Name based on location
• Pleura of lungs
• Pericardium of heart
• Peritoneum of abdominopelvic cavity

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SEROUS MEMBRANES

• Produce serous fluid
• Blood filtrate hyaluronic acid secreted by
  mesothelium
• Lubricates facing surfaces of parietal and
  visceral layers

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NERVOUS TISSUE

• Main component of the nervous system
• Brain, spinal cord, and nerves
• Regulates and controls body functions
• Two main cell types
• Neurons
• Generate and conduct nerve impulses
• Supporting cells
• Non-conducting cells that support, insulate,
  and protect neurons

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MUSCLE TISSUE

• Highly cellular
• Well vascularized
• Responsible for most types of body movement
• Possess myofilaments
• Actin and myosin
• Three types
• Skeletal muscle
• Cardiac muscle
• Smooth muscle

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SKELETAL MUSCLE

• Skeletal muscle cells
• a.k.a., Muscle fibers
• Long, cylindrical cells
• Multinucleate
• Striated
• Voluntary

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SKELETAL MUSCLE

• Forms organs called skeletal muscles
• Packaged by sheets of connective tissue
• Attached to bones of skeleton
• Contract to pull on bones or skin
• Movement results

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CARDIAC MUSCLE

• Found only in the wall of the heart
• Contractions propel blood through blood vessels
• Cardiac muscle cells
• Myocytes
• Striated
• Uninucleate
• Branching
• Involuntary

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SMOOTH MUSCLE

• Found mainly in walls of hollow organs
• e.g., Intestines, esophagus, blood vessels, etc.
• Contractions squeeze substances through these
  organs
• No visible striations
• Smooth muscle cells
• Spindle shaped
• Uninucleate
• Involuntary

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BODY DEFENSES

• Mechanical barriers are the bodys first line of
  defense against injury and infection
• Skin and mucous membranes
• Respiratory cilia
• Acids secreted into stomach and from skin
• Tissue injury breaches this first line of defense
• Stimulates inflammatory and immune responses
• Second and third lines of defense, respectively
• Tissue is ultimately repaired

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TISSUE REPAIR

• Injured cells release growth factors
• Stimulate cells to divide and migrate
• Two major tissue repair means
• Regeneration
• Replacement of destroyed tissue with same type of
  tissue
• Fibrosis
• Replacement with fibrous connective tissue (scar
  tissue)
• Type of repair dependent upon
• Type of tissue damaged
• Severity of injury

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TISSUE REPAIR

• Inflammation
• Injured cells, macrophages, and mast cells
  release inflammatory chemicals
• Dilation and increased permeability of
  capillaries
• Plasma and leukocytes enter injured area
• Plasma proteins form clot
• Halts blood loss
• Isolates injured area
• Prevents spread of microbes
• Forms scab

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TISSUE REPAIR

• Organization
• Blood clot replaced by granulation tissue
• Capillaries
• Proliferating fibroblasts
• Produce growth factors, collagen fibers
• Pull margins of wound together
• Macrophages
• Digest clot
• Granulation tissue ultimately becomes scar
  tissue

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TISSUE REPAIR

• Permanent Repair
• Surface epithelium begins to regenerate
• Grows under scab
• Scab ultimately detaches
• Epithelium fully regenerated
• Fibrous material beneath epithelium matures and
  contracts
• Scar tissue beneath epithelium
• Scar may be visible or not

87
TISSUE REPAIR

• The regenerative capacity of different tissues
  varies widely
• Some tissues regenerate extremely well
• e.g., Epithelial, bone, areolar connective
  tissue, blood-forming tissue
• Some tissues have a moderate regenerative
  capacity
• e.g., Smooth muscle, dense regular connective
  tissue
• Some tissues have a weak regenerative capacity
• e.g., Skeletal muscle, cartilage
• Some tissues have a virtually no functional
  regenerative capacity
• e.g., Cardiac muscle, nervous tissue

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TISSUE REPAIR

• In non-regenerative tissue and severe wounds,
  damaged tissue is replaced by fibrosis
• Resulting scar tissue is strong, but lacks
  flexibility, elasticity, and function of normal
  tissue
• How do you think function might be impaired?