INTRODUCTION TO HISTOLOGY - PDF by wulinqing

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									   INTRODUCTION TO
      HISTOLOGY
    http://camilolab.slu.edu/444/histology.html




Histology: The Study of Tissue


       General Histology: tissue structure only


       Special Histology (organology) -- arrangement of tissues in
                                         organs


VETEBRATE HISTOLOGY (this course)
       Mammalian Histology
       Human Histology




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                  Origins of Tissues –the subject of Embryology
Fertilized egg cleaves forming a mass of cells –smaller and smaller in size
         Become arranged into three superimposed layers (germ layers)
                  External:          Ectoderm
                  Middle:            Mesoderm
                  Inner:


Histogenesis results in four tissue types:
         Epithelial Tissues –from all three germ layers
         Supporting Tissues –from mesoderm
         Muscle Tissues - from mesoderm
         Nervous Tissues –from ectoderm




A tissue is a group of similar cells (together with their cell
products), specialized in a common direction and set apart
for the performance of a common function.




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Epithelium –sheet like coverings with one surface free, one surface attached


Supporting tissues –connect, bind, support


Muscle tissues –respond to stimuli –contract


Nervous tissues –irritable –conduct nervous impulses –waves of excitation


Vascular tissue - ?
Lymphoid tissue - ?




                                 Role of Water

Human Body is 70% water
         Water content varies with tissue type
                  Blood and muscle - more
                  Fat and Bone - less
         Protoplasm is generally 75% water
                  Free
                  Bound to other components
         Intracellular water = 50% of total body weight
         Extracellular fluid bathes cells = 15% of total body weight
                  Extremely important component –holds anabolic materials and
                  end products of catabolism.
Firm substances –on cell surfaces or embed cells (interstitial substances = ground
substances or matrix)




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                         EPITHELIA
                 The Covering/Lining Tissues


Cells contiguous
Basement Membrane
Occurrence: wherever free surfaces exist




                        Types of Epithelia (classification)
Layering:
        Simple –a single layer of cells resting on a basement membrane
        Pseudostratified –a single layer of cells but looks like 2 or more layers
        Stratified –several to many layers of cells




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                         Types of Epithelia (classification)
Cell Shape:
        Squamous –cells are flat plates
        Cuboidal –cells have about the same height and width
        Columnar –cells are taller than they are wide




STRATIFIED EPITHELIA


Surface layer defines stratified epithelia:


   Stratified squamous epithelium; the superficial cells are flattened.

   Stratified cuboidal epithelium; the superficial cells are roughly cubical.

   Stratified columnar epithelium; the superficial cells are elongated prisms.




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Special names used for two epithelia of wide occurrence.

Simple epithelia, characteristic of definite locations.

         Endothelium: simple squamous lining of blood vessels and lymphatics.

         Mesothelium: simple squamous lining of body cavities.

         Mesenchymal epithelium: denotes the simple layer of squamous cells that
         lines special spaces

                   Spaces arise as clefts in the embryonic mesenchyme.

                   Subdural and subarachnoid spaces; perilymphatic spaces of the
                   ear; anterior chamber of the eyeball.

                   Indistinguishable structurally from mesothelium.




Other sometimes confusing terms used

False epithelium: the membrane that encloses the cavities of joints and bursae.

          Layer made of white fibers and scattered, flattened fibroblasts.

          It is not epithelium, but connective tissue.


Epithelioid: adjective applied to layers of cells that imitate epithelium.

          Example: connective-tissue osteoblasts and odontoblasts, arranged as
          sheets in developing bone; ependymal cells lining the central canal of the
          spinal cord.




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 SIMPLE SQUAMOUS EPITHELIUM


 Found:
           Body cavities (mesothelium).
           Cardio-vascular and lymphatic systems (endothelium).
           Smallest ducts of many glands.
           Terminal respiratory ducts and air sacs.
           Membranous labyrinth (except sensory areas); tympanic cavity.




Simple Cuboidal Epithelium

FOUND:

          Many glands; portions of their ducts.
          Pigmented epithelium of retina; epithelioid covering of chorioid plexus.
          Germinal layer of ovary.




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Simple Columnar Epithelium


Found:

         Stomach and intestine.
         Many glands; portions of the ducts of some glands; gall bladder.
         Uterine tube and uterus.
         Bronchioles.




Specialized Types of Epithelium

Four Types of Specialization:
1. Glandular
         Unicellular
         Multicellular
2. Ciliated
3. Pigmented
4. Neuro-epithelium




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Pseudostratified Epithelium
Found:
         Larger ducts of glands opening onto a stratified epithelial surface.
         Nasal cavity; trachea; bronchi.
         Much of male urethra; some of female urethra.
         Most of male sexual duct.




Pseudostratified Epithelium


Fully developed/specialized pseudostratified epithelium, three cell types:


         Basal cells
         Fusiform cells
         Columnar cells.




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                      STRATIFIED EPITHELIA

This type contains truly superposed cells.

Subtypes are named according to the shape of the surface
cells alone.




Stratified Squamous Epithelium
Found:

         Wherever there is exposure to friction, mechanical insult or drying.

         Skin
         Conjunctiva (in part)
         Cornea
         External acoustic meatus
         Mouth
         Esophagus
         Anus
         Urethra (near outlet)
         Vagina.




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A few layers to many


Few: Cornea
Many: Epidermis




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Intercellular Bridges




Stratified Cuboidal Epithelium

     Testis tubules; vesicular (Graafian) follicles of ovary.
     Ducts of sweat glands; sebaceous glands.
     Intermediate zones of some regions, such as the urethra and
              conjunctiva.
     Urinary tract from kidney to urethra (transitional epithelium).




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Stratified Columnar Epithelium

Found:
         Pharynx (in part); larynx (in part).
         Urethra (in part).
         Excretory ducts of salivary and mammary glands (in part).

         In general, where columnar or pseudostratified epithelium meets
         stratified squamous epithelium.)




                                     Simple Columnar
               Stratified Squamous




                                         Stratified Columnar




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Epithelial Cells = typical cells
Nucleus –conforms to shape of cell
        squamous  flattened disk
        cuboidal  spheroidal
        columnar  elongate/ovoid
Cytoplasm –nothing unusual –typical organelles
Polarity –free vs. attached ends differ
        distal (surface) more highly speicalized
        columnar cells –nucleus near base and
        mitochondria orient long dimension of cell




                      Epithelial Cell Surfaces

Free surface  air or fluid
Lateral surface  contact –cells of same type
Basal surface  connective tissue substrate


Simple epithelia –all cells have all three surfaces
Stratified epithelia –no cell has more than 2 surface relations




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                            FREE SURFACE


    Cytoplasmic specializations
          Condensed border  blends with “     ordinary” cytoplasm below
          Superficial condensation blends into ordinary cytoplasm
          Stains more deeply
          Non-motile processes  Project from free surface;
          Microscopic and submicroscopic; Absorption or sensory funcitons
                 PROCESSES RELATED TO ABSORPTION
                 PROCESSES RELATED TO SECRETION
                 SENSORY HAIRS




.

Absorption –microvilli

                 On intestinal epithelium = striate border,
                 vertical parallel rodlets, uniform length

                 On kidney tubules = brush border, coarser,
                 longer filaments, not uniform length, amorphous
                 substance between microvilli




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     Secretion –delicate, short microvilli
           Glands of stomach and uterus (EM)
           Longer,hair-like in male sex ducts
           Dropets of secretion ooze from tip = non-motile
                 cilia or stereocilia


     Sensory Hairs –Sensory epithelial cells
          Hair-like receptor processes
          Smell, Taste, Hearing, Equilibration




      MOTILE PROCESSES (CILIA) lashing protoplasmic processes
              variable length and fineness
              numbers vary –up to 100+ on a cell
              single, long one = flagellum


              Respiratory tract, uterine tube, uterus, efferent ductules of
              testis

Secreted Plates
      more or less solid formed-substances
      secreted by cell
      often infiltrated with a hard substance (clam shell; chitin of beetle
              Mammals  enamel of tooth, lens capsule, tectorial
              membrane of ear.




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LATERAL SURFACES

    Minute space between epithelial cells
            Fluids, leucocytes can penetrate
    Intercellular bridges –tonofibrils; desmosomes
    Intercellular cement
    Teminal bars
    Interlocking membranes




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Basal surface
  Extensive infoldings of plasma membrane
  On bed of connective tissue –firm attachment
      1. Epithelium  processes into C.T.
      2. C.T.  projections up into epithelium
      3. Basement membrane




Basement Membrane = Membrana Propria

      Usual method of attachment of epithelium
      Thickness varies with location
      Structureless, hyaline ground substance
              Reticular fibers below and in Basement Membrane
              (Reticulin stains, esp. PAS technique)
              PAS –affinity for mucopolysaccarides
      Simple cementing; tooth-like projections




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BLOOD VESSELS; NERVE FIBERS; WANDERING CELLS


Repair and Replacement




                 FUNCTIONS OF EPITHELIA
 PROTECTION
 SECRETION
 EXCRETION
 ABSORPTION
 LUBRICATION
 SENSORY RECEPTION
 REPRODUCTION




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