Chapter 4 Tissues and Histology

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Chapter 4Tissues and Histology

• Tissues - collections of similar cells and the
  substances surrounding them
• Tissue classification based on structure of
  cells, composition of noncellular extracellular
  matrix, and cell function
• Major types of adult tissues
• Epithelial
• Connective
• Muscle
• Nervous
• Histology Microscopic Study of Tissues
• Biopsy removal of tissues for diagnostic
  purposes
• Autopsy examination of organs of a dead body to
  determine cause of death

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Embryonic Tissue

• 3 major germ layers that form the embryonic disc
  (source of stem cells)
• Endoderm
• Inner layer
• Forms lining of digestive tract and derivatives
• Mesoderm
• Middle layer
• Forms tissues as such muscle, bone, blood vessels
• Ectoderm
• Outer layer
• Forms skin and neuroectoderm

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I. Epithelial Tissue

• Cellularity - Consists almost entirely of cells
• Covers body surfaces, lines hollow organs, and
  forms glands
• Outside surface of the body
• Lining of digestive, respiratory and urogenital
  systems
• Heart and blood vessels
• Linings of many body cavities
• Polarity - Has apical, basal, and lateral
  surfaces
• Rests on a basement membrane
• Specialized cell contacts bind adjacent cells
  together
• Avascular - no blood vessels
• Regenerative -Replaces lost cells by cell division

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Functions of Epithelia

• Protecting underlying structures e.g.,
  epithelium lining the mouth
• Acting as barriers e.g., skin
• Permitting the passage of substances e.g., cells
  lining air sacs in lungs and nephrons in kidney
• Secreting substances e.g., pancreatic cells
• Absorbing substances e.g., lining of stomach and
  small intestine

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Special Characteristics of Epithelia
Figure 4.1
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Classification of Epithelium

• Number of layers of cells
• Simple- one layer of cells. Each extends from
  basement membrane to the free surface
• Stratified- more than one layer.
• Pseudostratified- tissue appears to be
  stratified, but all cells contact basement
  membrane so it is in fact simple
• Shape of cells
• Squamous- flat, scale-like
• Cuboidal- about equal in height and width
• Columnar- taller than wide

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Classifications of Epithelia
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Simple Squamous Epithelium
Figure 4.3a
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Simple Cuboidal Epithelium
Figure 4.3b
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Simple Columnar Epithelium
Figure 4.3c
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Pseudostratified Ciliated Columnar Epithelium
Figure 4.3d
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Stratified Epithelia

• Contain two or more layers of cells
• Regenerate from below
• Major role is protection
• Are named according to the shape of cells at
  apical layer

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Stratified Squamous Epithelium

• Description
• Many layers of cells squamous in shape
• Deeper layers of cells appear cuboidal or
  columnar
• Thickest epithelial tissue adapted for
  protection

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Stratified Squamous Epithelium

• Specific types
• Keratinized contain the protective protein
  keratin
• Surface cells are dead and full of keratin
• Non-keratinized forms moist lining of body
  openings

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Stratified Squamous Epithelium

• Function Protects underlying tissues in areas
  subject to abrasion
• Location
• Keratinized forms epidermis
• Non-keratinized forms lining of esophagus,
  mouth, and vagina

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Stratified Squamous Epithelium
Figure 4.3e
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Transitional Epithelium
Figure 4.3h
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Epithelium Glandular

• A gland is one or more cells that makes and
  secretes an aqueous fluid
• Two types of glands formed by infolding of
  epithelium
• Endocrine no contact with exterior of body
  ductless produce hormones (pituitary, thyroid,
  adrenals, pancreas)
• Exocrine open to exterior of body via ducts
  (sweat, oil)
• Exocrine glands classified either by structure or
  by the method of secretion
• Classified by structure
• Unicellular goblet cells
• Multicellular sweat, oil, pituitary, adrenal

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Multicellular Exocrine Glands

• Classified on the basis of types of ducts or mode
  of secretion
• Types of ducts
• Simple ducts with few branches
• Compound ducts with many branches
• If ducts end in tubules or sac-like structures
  acini. Pancreas
• If ducts end in simple sacs alveoli. Lungs

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Lateral Surface Features

• Tight junctions
• Desmosomes
• Gap junctions

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Membrane Junctions Tight Junction

• Integral proteins of adjacent
• cells fuse together
• Completely encircle the cell
• and form an adhesion belt.
• Form an impermeable
• junction.
• Common near apical region

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Lateral Surface Features Cell Junctions

• Desmosomes two disc-like plaques connected
  across intercellular space
• Plaques of adjoining cells are joined by proteins
  called cadherins
• Proteins interdigitate into extracellular space
• Intermediate filaments insert into plaques from
  cytoplasmic side

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Membrane Junctions Desmosome
Linker proteins extend from plaque like teeth of
a zipper. Intermediate filaments extend across
width of cell.

• Common in superficial layers of skin skin
• peels after a sunburn
• Reduces chance of tearing, twisting, stretching

Figure 3.5b
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Membrane Junctions Gap Junction

• Connexon proteins are trans-
• membrane proteins.
• Present in electrically excitable
• tissues (heart, smooth muscle)

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Basal Feature The Basal Lamina

• ? Noncellular supporting sheet between the
  epithelium and the connective tissue deep to it
• ? Consists of proteins secreted by the epithelial
  cells
• ? Functions
• ? Acts as a selective filter, determining which
  molecules from capillaries enter the epithelium
• ? Acts as scaffolding along which regenerating
  epithelial cells can migrate
• ? Basal lamina and reticular layers of the
  underlying connective tissue deep to it form the
  basement membrane

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Epithelial Surface Features

• Apical surface features
• Microvilli finger-like extensions of plasma
  membrane
• Abundant in epithelia of small intestine and
  kidney
• Maximize surface area across which small
  molecules enter or leave
• Cilia whip-like, highly motile extensions of
  apical surface membranes
• Movement of cilia in coordinated waves

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Connective Tissue

• Most diverse and abundant tissue
• Main classes
• Connective tissue proper
• Cartilage
• Bone tissue
• Blood
• Characteristics
• Mesenchyme as their common tissue of origin
  (mesenchyme derived from mesoderm)
• Varying degrees of vascularity
• Nonliving extracellular matrix, consisting of
  ground substance and fibers
• Cells are not as abundant nor as tightly packed
  together as in epithelium

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Connective Tissue Embryonic Origin
Figure 4.5
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Functions of Connective Tissue

• Enclose organs as a capsule and separate organs
  into layers. Areolar
• Connect tissues to one another. Tendons and
  ligaments.
• Support and movement. Bones.
• Storage. Fat.
• Insulation. Fat.
• Transport. Blood.
• Protection. Bone, cells of the immune system.

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Structural Elements of Connective Tissue

• Ground substance unstructured material that
  fills the space between cells
• Fibers collagen, elastic, or reticular
• Cells fibroblasts, chondroblasts, osteoblasts,
  hematopoietic stem cells, and others

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Connective Tissue Cells

• Fibroblasts - secrete the proteins needed for
  fiber synthesis and components of the
  extracellular matrix
• Adipose or fat cells (adipocytes). Common in some
  tissues (dermis of skin) rare in some
  (cartilage)
• Mast cells. Common beneath membranes along small
  blood vessels. Can release heparin, histamine,
  and proteolytic enzymes in response to injury.
• Leukocytes (WBCs). Respond to injury or
  infection
• Macrophages. Derived from monocytes (a WBC).
  Phagocytic provide protection
• Chondroblasts - form cartilage
• Osteoblasts - form bone
• Hematopoietic stem cells - form blood cells
• Undifferentiated mesenchyme (stem cells). Have
  potential to differentiate into adult cell types.

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Extracellular Matrix - ECM

• ECM has 3 major components
• 1. Protein fibers 2. Ground substance 3.
  Fluid
• Protein fibers
• Collagen fibers. Composed of the protein
  collagen. Strong, flexible, inelastic great
  tensile strength (i.e. resist stretch). Perfect
  for tendons, ligaments
• Elastic fibers. Contain molecules of protein
  elastin that resemble coiled springs. Returns to
  its original shape after stretching or
  compression. Perfect for lungs, large blood
  vessels
• Reticular fibers. Formed from fine collagenous
  fibers form branching networks (stroma). Fill
  spaces between tissues and organs.

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Ground Substance

• Interstitial (tissue) fluid within which are one
  or more of the molecules listed below
• Hyaluronic acid a polysaccharide. Very slippery
  serves as a good lubricant for joints. Common in
  most connective tissues.
• Proteoglycans protein and polysaccharide
  complex. Polysaccharides called
  glyocosaminoglycans (chondroitin sulfate, keratin
  sulfate). Protein part attaches to hyaluronic
  acid. Able to trap large amounts of water.
• Adhesive molecules hold proteoglycan aggregates
  together. Chondronectin in cartilage, osteonectin
  in bone, fibronectin in fibrous connective
  tissue.
• Functions as a molecular sieve through which
  nutrients diffuse between blood capillaries and
  cells

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Embryonic Connective Tissue

• Mesenchyme source of all adult connective
  tissue.
• Derived from mesoderm
• Delicate collagen fibers embedded in semifluid
  matrix
• Mucus found only in the umbilical cord.
  Whartons jelly.

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Areolar Connective Tissue
Figure 4.12b
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Adipose Tissue
Figure 4.12c
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Reticular Connective Tissue
Figure 4.12d
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Dense Irregular Connective Tissue
Figure 4.12e
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Dense Regular Connective Tissue
Figure 4.12f
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Elastic Connective Tissue

• Bundles and sheets of collagenous and elastic
  fibers oriented in multiple directions
• In walls of elastic arteries (aorta), lungs,
  vocal ligaments
• Strong, yet elastic allows for recoil of tissue
  after being stretched

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Connective Tissue Cartilage

• Composed of chondrocytes (cells) located in
  matrix-surrounded spaces called lacunae.
• Type of cartilage determined by components of the
  matrix.
• Firm consistency.
• Ground substance Proteoglycans and hyaluronic
  acid complexed together trap large amounts of
  water (microscopic sponges). Allows tissue to
  spring back after being compressed.
• Avascular and no nerve supply. Heals slowly.
• Perichondrium. Dense irregular connective tissue
  that surrounds cartilage. Fibroblasts of
  perichondrium can differentiate into
  chondroblasts (cartilage-forming cells)
• Types of cartilage
• Hyaline
• Fibrocartilage
• Elastic

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Hyaline Cartilage
Figure 4.12g
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Elastic Cartilage
Figure 4.12h
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Fibrocartilage
Figure 4.12i
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Bone Tissue
Figure 4.12j
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Blood Tissue
Figure 4.12k
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Muscle Tissue

• Characteristics
• Cells are referred to as fibers
• Contracts or shortens with force when stimulated
• Moves entire body and pumps blood
• Types
• Skeletalattached to bones
• Cardiac muscle of the heart.
• Smooth muscle associated with tubular structures
  and with the skin. Nonstriated and involuntary.

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Skeletal Muscle Tissue
Figure 4.14a
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Cardiac Muscle Tissue
Figure 4.14b
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Smooth Muscle Tissue
Figure 4.14c
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Nervous Tissue
Figure 4.15
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Tissues and Aging

• Cells divide more slowly
• Collagen fibers become more irregular in
  structure, though they may increase in number
• Tendons and ligaments become less flexible and
  more fragile
• Elastic fibers fragment, bind to calcium ions,
  and become less elastic
• Arterial walls and elastic ligaments become less
  elastic
• Changes in collagen and elastin result in
• Atherosclerosis and reduced blood supply to
  tissues
• Wrinkling of the skin
• Increased tendency for bones to break
• Rate of blood cell synthesis declines in the
  elderly
• Injuries dont heal as readily