Epithelial Tissue

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					EPITHELIAL TISSUES:
 1. Apical: an upper or free surface exposed to the body exterior or the cavity of an
    internal organ.
 2. Basal Surface: a lower or attached surface near the base or interior of a
    structure; nearest the lower side or bottom of a structure.
 3. Cilia: Tiny, hair-like projections on cell surfaces that move in a wave-like
    manner, helping to sweep away particles or fluid.
 4. Duct: canal or passageway; a tubular structure that provides an exit for the
    secretion of a gland or for conducting any fluid.
 5. Endocrine Glands: glands that lose their surface connection (duct) and are
    therefore called, “ductless glands”. Their secretions (all hormones) empty directly
    into the blood. Hormones secreted from the GI tract cause the pancreas to
    release digestive enzymes. ***Internally secreting.
 6. Excrete: the elimination of waste products from the body.
 7. Exocrine Glands: glands that retain their ducts through which their secretions
    empty to an epithelial surface i.e. sweat/oil glands, salivary glands, liver (bile
    secretions) and pancreas (digestive enzymes). ***Externally secreting.

 8. Epithelial Tissue: AKA epithelia. COVERS SURFACES: lines cavities and
    tubules. Generally marks off the insides from the outsides. ALL epithelial tissue
    exhibit apical-basal polarity.

                    Four Primary Tissue Types:
                           Epithelium
                           Connective Tissue
                           Muscle Tissue
                           Nervous Tissue

                    Functions of Epithelial Tissue:
         Protection  bacterial invasion and chemical injury. Lining of respiratory
          tract is ciliated to sweep dust and other foreign particles away from the
          lungs.
         Absorption  small intestine
         Filtration  kidney tubules
         Excretion kidney tubules
         Secretion  kidney tubules. Also a specialty of glands
         Sensory reception  skin = pressure and temperature
              Characteristics [which distinguishes epithelial tissue from other types]:

           Polarity: this is a generalized term that refers to non symmetrical. All
            membranes will always have one free surface APICAL surface, or the
            highest point, usually at the pointed end of an object. This area will typically
            be significantly different from the basal surface.
           Cellularity and specialized contacts: cells fit closely together to form
            membranes. They are bound by special junctions.
           Supported by connective tissue: cells are attached to and supported by an
            adhesive BASEMENT MEMBRANE. This membrane is an amorphous
            (without definite form) material, secreted partly by epithelial cells (basal
            lamina) and connective tissue cells (reticular lamina) that lie adjacent to
            each other.
           Avascularity: epithelial tissues have no blood supply of their own
            AVASCULAR. They are depended upon nutrients diffusing by underlying
            connective tissue. The ONLY EXCEPTION is glandular epithelia tissue,
            which is very vascular***.
           Regeneration: If well nourished, epithelial tissue will regenerate
            themselves. This means they are very well suited for friction.

    Classification of epithelia tissue:  TWO CRITERIA
        Number of layers AKA arrangement
                   Simple epithelial: ONE layer of cells, attached to a
                    basement membrane
                   Stratified [layers]: TWO or more layers

           Cell shape: ***there are 5 general types of epithelial tissue:
     SQUAMOUS, CUBOIDAL, COLUMNAR, PSEUDOSTRATIFIED, TRANSITIONAL.
Squamous: scale like. Flattened cells with disc-shaped nuclei. Function allows the
passage of materials via diffusion and filtration. Protection is NOT important. Location 
kidney glomeruli, sacs of lungs, lining of heart, blood vessels, lymph vessels and lining of
ventral body cavities (serosa).

Cuboidal: cube like. Large, spherical cell, with central nuclei. Function secretion and
absorption. Location  kidney tubules, ducts and secretory portions of small glands and ovary
surface.

Columnar: column shaped. Tall cells with round to oval nuclei. Some cells bear cilia.
May contain mucus-secreting unicellular glands AKA goblet cells. Function absorption,
secretion of mucus, enzymes and other substances. Ciliated types propel mucus (or
reproductive cells) by ciliary action. Location  NON-CILIATED: mostly GI tract stomach to
anal canal, gall bladder, excretory ducts of some glands. May contain microvilli. CILIATED:
small bronchi, uterine tubes and some regions of the uterus.
***When “stratified” is combined with any of these cell types  generally refers to:
cells at the apical surface of the epithelial membraneNOT RESTING ON THE
BASEMENT MEMBRANE.
Stratified Squamous: the most widespread of stratified epithelia. Composed of several cell
layers, is thick and well suited for a protective role. The free or apical surface is squamous. But
lower layers are composed of cuboidal or columnar. Function: protection in areas subject to
wear and tear. Location: external part of skin and extends a short distance into every body
opening that is directly continuous with the skin. The outer layer, or epidermis is keratinized or
the surface cells contain keratin a tough protective protein. Other stratified squamous epithelia
of the body are non-keratinized.

Stratified Cuboidal: generally, two layers of cube-like cells. Function: Protection.
Location: Largest ducts of sweat glands, mammary glands and salivary glands.

Stratified Columnar: Several cell layers. Basal cells are usually cuboidal. The superficial
cells are elongated and columnar. Function: Protection and secretion. Location: Rare in the
body. Small amounts in male urethra and large ducts in some glands.

Pseudostratfied : SIMPLE COLUMNAR One layer of cells that vary in height. The nuclei
lie at different levels above the basement membrane. Some of the cells do not reach the free
surface. The nuclei are seen at different levels. This type of epithelial tissue may contain
goblet cells and may bear cilia. Function secretion particularly mucus by ciliary action.
Location  NON-CILIATED: male sperm carrying ducts and the ducts of large glands.
CILIATED: trachea and upper respiratory tract.

Transitional [often ciliated]: Round, plump cells capable of sliding over one another,
allowing an organ to stretch. Resembles both stratified squamous and stratified cuboidal.
Basal cells = columnar. LocationONLY FOUND in urinary system OR organs that require
periodic distention bladder, urethra or ureter.




   9. Filtration: the passage of a solvent and dissolved substances through a
       membrane or filter.
   10. Gland: a organ that is specialized to secrete or excrete substances for further
       use in the body OR for elimination.
   11. Histology: the study of the tissues. Histology complements the study of gross
       anatomy by providing the structural basis for a study of organ physiology.
   12. Microvilli: Tiny projections on the free or apical surface of some epithelial tissue
       cells designed to increase surface area for absorption.
   13. Secrete: 1) the passage of material formed by a cell to its exterior. 2) cell
       product that is transported to the exterior of the cell.
   14. Tissues: groups of cells that are similar in structure and function. Four
       PRIMARY types of tissues: EPITHELIUM, CONNECTIVE TISSUE, NERVOUS
       TISSUE and MUSCLE.

				
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posted:11/20/2011
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