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Lesson 1 - Introduction to Tissues and Epithelial Tissue

Student Performance Objectives
1. List the 4 basic tissue types and describe their basic functions.
2. Define basement membrane, intercellular substance and tight junctions.
3. Explain the difference between a simple and a stratified epithelial layer.
4. For each of the 4 following types of epithelium, draw a sketch of the tissue and list its major
    functions: simple squamous, stratified squamous, simple cuboidal, transitional, simple
    columnar, and pseudostratified columnar epithelium.

Lesson Outline
A. Introductory Concepts
    1. The cells composing an animal's body form the organs visible to the unaided eye.
    2. Using a microscope we observe that each organ of the body is actually composed of groups of cells called tissues.
    3. The 4 basic tissue types of the human body are:
        a. Epithelial tissue- form body surfaces
            (1) Outside surfaces - skin's upper layer or epidermis.
            (2) Inside surfaces - surfaces of hollow organs like the stomach and
                 small intestine - both their inner and outer surfaces.
        b. Muscular tissue- by contracting and relaxing, these tissues provide movement for the body as a whole and for its internal parts.
            (1) Skeletal (striated) muscle - the voluntary muscle that attaches to and moves the skeleton at the joints, soft tissues of the face providing us with facial expressions, and controlling some body openings as sphincters.
            (2) Smooth muscle - the involuntary muscles found in the walls of hollow
                 organs like the blood vessels (controlling blood flow and pressure) and viscera (providing for control of movement of food and waste through the alimentary canal).
            (3) Cardiac muscle - the muscle of the wall of the heart which provides
                 the propulsive force for the flow of blood throughout the body.
        c. Nervous tissue- through the properties of irritability and conductivity, these tissues serve as the body's means of detecting stimuli (sensation), sending electrochemical messages from one region to another, and, in the brain, analyzing information.
        d. Connective tissue - these tissues join other tissues together in various ways and
            generally form a fabric in which all our cells are physically supported.
B. Epithelial tissues: The most common epithelial tissues are considered.
    1. In general: 

        a. Underlying the cells of an epithelial layer is a basement membrane, a thin
            connective tissue layer that binds the layer of epithelial cells with the
            underlying layer of connective tissue.
        b. There is very little or no space between the cells of an epithelial layer. Contrast
            to connective tissue where there is a great deal of space between cells and
            much intercellular substance.
        c. The cellular borders joining each cell to the next possess tight junctions firmly
            binding the cells together.
    2. Squamous epithelium
               a. Simple - layer of flattened cells forming a thin sheet. Found in:
            (1) Serous membranes like the peritoneum of the abdominal cavity and the pleurae of the pleural cavities.
            (2) The endothelium lining the inner wall of blood vessels.
            (3) The endocardium lining of the inner surface of the heart.
        b. Stratified - several layers of cells forming thicker sheets where more
            protection is needed. Can be keratinized or non-keratinized
            (1) Keratinized stratified squamous - the skin's upper layer, the epidermis.
            (2) Non-keratinized - forming the inner lining of the mouth, anus and the
    3. Cuboidal epithelium
        a. Simple - a single layer of cells shaped like cubes. Found forming the
            kidney's tubules where absorption and secretion are important.
b. Stratified - several layers of cubically shaped cells. Forming the wall of the
            urinary bladder, such a stratified layer is called transitional epithelium because the cells undergo
            accommodate varying quantities of urine.
   4.  Simple columnar epithelium - a single layer of rectangular-shaped cells can provide a
        measure of protection and permit transport of molecules across the layer's surface.
        Found lining much of the digestive tract after the mouth: most of the esophagus, the
        stomach, small intestine, and the large intestine.

        a. The simple columnar layer found in the digestive tract also contains goblet cells that produce and secrete mucus. Mucus lubricates the passage of food along the surface and protects the
            underlying cellular layer.
        b. The columnar epithelial cells are tightly bound to each other through tight junctions - free passage of undigested molecules from the digestive chambers to the tissues underlying the cell surface or
             the blood is prevented. Only digested molecules are specifically absorbed. by the epithelial surface.
    5. Pseudostratified columnar epithelium - so called because the layer appears to be
        stratified but is actually only one layer of cells.

        a. Found lining the respiratory passages from trachea to tiny bronchioles deep in
            the lungs.
        b. The cells are ciliated.
        c. Goblet cells are abundant and the ciliated cells beat with the power stroke
            upward away from the lungs toward the throat thus creating an upward moving
            "conveyer belt" of mucus that continually cleans the lungs of inhaled particles
            of dirt.