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HISTOLOGY THE STUDY OF TISSUE The primary tissue classes. 1. All tissues consist of extracellular material ( matrix ) and cells. 2. Spaces between cells and fibers within a tissue are filled with tissue fluid (also known as extracellular or interstitial fluid). Embryonic Tissues 1. All mature tissues arise from the three primary germ layers of the embryo. a. Ectoderm gives rise to the epidermis and nervous system b. Endoderm gives rise to the lining of the digestive and respiratory tracts and to the digestive glands. c. Mesoderm gives rise to muscle, bone, blood and other tissues. Early embryonic tissue gives rise to mesenchyme, which I turn produces most of the permanent connective tissue, as well as muscle. Interpreting Tissue Sections. 1. Knowledge of tissues is obtained from the proper interpretation of their observation. 2. Specimens are first preserved in fixative, and then cut into histological sections. Last, they are stained and observed. 3. Various angles of observation include longitudinal, cross, transverse and oblique sections. Epithelial Tissue A. Epithelial tissues are classified as simple or stratified. a. Epithelial tissue covers the body surface, lines body cavities and covers many organs. b. It adheres to underlying tissue by means of basement membrane made up of collagen and glycoproteins. B. Simple Epithelia a. Simple squamous epithelium is made up of one layer of cells, all adhering to the basement membrane.
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b. Simple squamous epithelium is one cell layer thick and is well- adapted to transporting substances across it. It has a single centrally located nucleus. c. Simple squamous epithelium lines the alveoli. The walls of capillaries are made up of the same tissue, but it is called endothelium. d. Most simple squamous epithelium is called mesothelium and covers the external surfaces of many body organs and cavities. C. Simple cuboidal epithelium is made up of a single layer of cube- shaped cells with a centrally located nucleus. This type is common in glands, and lines kidney tubules and lung bronchioles (where it is ciliated). D. Simple columnar epithelium is a single layer of vertically elongated thin cells. a. Nuclei are present in the basal one-third of the cell. b. This tissue often has a secretory function, but absorbs nutrients in the small intestines. It is also found lining the uterine tubes and in the uterus, stomach and large intestine. c. In pseudostratified epithelium, not every cell reaches the basement membrane. This type is abundant in the respiratory tract where it is ciliated and produces mucus. It is also found within male reproductive tract and often contains goblet cells. E. Stratified Epithelia a. The surface cells of stratified squamous epithelium are flattened while deeper cells take on a variety of shapes. It is the tissue of the epidermis of the skin. b. Within the epidermis, older cells become keratinized.
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This note was uploaded on 04/17/2008 for the course BIOL 211 taught by Professor Wilson during the Fall '07 term at Winona.

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