SCIT 1407/BIOL 2401
I. EPITHELIAL TISSUE: Only exists in three cell shapes – flat or squamous, cuboidal & columnar. This tissue covers or lines other tissues or produces tubes. Epithelial tissue always rests on a basement membrane. The characteristics are: lack of visible interstitial space, many cells, and no blood vessels. A. Simple Squamous: (kidney slide). Look in the outer edge or cortex of the kidney to find a Bowman’s capsule. The lining of the Bowman’s capsule is a single layer of flat squamous cells. These cells are on edge so you can see how flat they really are. B. Stratified Squamous: Two types: Keratinized (skin slide) Multiple layers of living cells that appear columnar at the basement membrane and become squamous as they progress upward. Top cells are dead. Non-keratinized (esophagus slide). Like keratinized but top cells are alive and the living tissue is much thicker than the keratinized stratified squamous. On both tissues notice the change in color from the basement membrane to the top. Why is this? C. Simple Cuboidal: (kidney slide). Large cube shaped cells that almost always make tubes. In this slide almost all the cells are simple cuboidal. Notice the cross walls are so thin they seldom are seen with the light microscopes. All you observe is a group of large nuclei in a circle. D. Stratified Cuboidal: (skin slide). Unlike simple cuboidal, stratified cuboidal epithelium always make tubes with usually 2 but no more than 3 rows of cells. The only stratified cuboidal cells you will see this semester will be the cells that make a sweat gland. The sweat gland is unique because some of the cells are active glandular cells while the rest are non-active duct cells. The active cells swell up to produce sweat and therefore they are hard to identify as epithelial tissue. Always look for the duct cells, which drain the sweat to the surface of the skin. The ducts contain two rows of cells. E. Simple Columnar: (intestine slide & ciliated columnar slide). These cells are always taller than wide. In the body they perform a variety of functions from absorption and excretion to simply moving mucus. The intestinal slide is a complex slide with many tissue types in it. Find the tissue covering the long fingers. The fingers are called villi and they are lined with simple columnar. These cells are absorptive cells that have exceptionally long microvilli called a brush border on the top surface. Use your fine focus to see a color shift as the light is refracted through the microvilli. The large fat cells wedged between the columnar cells are called goblet cells and they secrete mucus. Ciliated columnar cells are found the reproductive tracts and the cilia are used to move sperm or the egg. Notice that some of these cells are not ciliated. F. Stratified Columnar: (no slide) This tissue is very rare in the body and therefore we will not discuss it here. You are not responsible for this tissue. G. Pseudostratified Ciliated Columnar: (trachea slide). This is a ciliated columnar epithelium that appears to have been compressed from side to side so the nuclei are at different levels thus appearing stratified hence the name pseudostratified. All of the cells do attach to the basement membrane therefore it is a simple epithelium. No stratified cells in the human body are also ciliated. In addition to the columnar and goblet cells you have already observed in other tissues there are small basal cells that can give rise to either columnar or goblet cells as the older cells are worn out. H. Transitional: (bladder and/or ureter). This is always a stratified tissue therefore stratified transitional is never used. Note the cells on the uppermost surface of the tissue. The cells are generally all the same shape but are often different sizes from the basement membrane to the surface with the largest cells often on the surface. When...
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