This lab is broken down into three sections: Epithelial Tissue, Connective Tissue, and Muscle & Nerve Tissue. For each section, read the background and answer any questions before you come to class, then in class sketch the specimens listed under each sketch circle. For your sketches, include the total magnification under which you viewed the specimen and be very detailed in your sketch.
Functions of Epithelium
Epithelium has two major functions: covering/lining and glandular: Epithelial tissue covers body structures or lines body spaces. One side of the epithelium is free (not attached) because it either faces outward (skin) or inward (lining). The other side of the epithelium is called the basement membrane and is attached to underlying connective tissue. Epithelia do not have their own blood supply; therefore, nutrients must diffuse through the basement membrane to reach the cells. Epithelia performing a glandular function are part of glands. Exocrine glands secrete substances into ducts which then empty onto epithelial surfaces (e.g. sweat glands, mammary glands). Endocrine glands secrete substances which then diffuse into the bloodstream (e.g. islet cells of pancreas secreting insulin).
Classification & Composition of Epithelium
Epithelium is classified by the number of cell layers and the shape of the cells in the outer layer. Number of Cell Layers
Simple – only one cell layer.
Stratified – more than one cell layer.
Pseudostratified – “false stratified”. Nuclei have separated into two layers due to cellular compaction. Cell Shapes
Squamous – like scales, wider than they are tall
Cuboidal - ~cube-shaped, tall as they are wide, may be more rounded than square Columnar – column-like cells, taller than they are wide Transitional – cells that can change shape as needed, usually stretch or compress (always stratified)
Epithelium can have some other unique characteristics that help us classify their types. Ciliated – cilia project along a cell’s free surface serving to propel material along the epithelial surface. Non-ciliated – cells lacking cilia
Keratinized – some cell layers in stratified squamous tissues will be dead and filled with keratin (tough, waterproof material); no nuclei will be in these cells. Non-keratinized – cell layers without keratinized cells; will see nuclei in the squamous cells along the free edge.
Locations of Epithelium
Different types of epithelia are found in various locations of the body depending on what functions they carry out. • Simple squamous epithelium – lines blood vessels, alveoli (air sacs) of lungs, and other areas requiring thin membranes; diffusion or filtration of water, gases, and other materials • Stratified squamous epithelium – outer part of skin and mucous linings of mouth, vagina, and esophagus; protective function, thus outer cells continually slough off and are replaced by underlying cells • Simple cuboidal epithelium - in secreting organs like glands and kidney tubules; specializes in secretion, water reabsorption, and ion movement • Simple columnar epithelium – linings specialized for absorption and secretion like reproductive tract, digestive tract, excretory ducts, and respiratory tract; often contains goblet cells which produce and secrete mucus for the purposes of lubrication and protection (see picture of ciliated cells above) • Ciliated pseudostratified epithelium – found in upper throat, upper respiratory tract, and parts of male urinary and reproductive tracts Transitional epithelium – able to stretch, so is found in areas dealing with large amounts of elastic stress such as the urinary bladder
Epithelium Sketches – for each of the...
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