Histology: Chapter 3:SIMPLE EPITHELIUM
A. SIMPLE EPITHELIUM. This type of epithelium has one layer of cells.
1. Simple squamous. This “pavement epithelium” has flattened scale-like or plate-like cells.
a. On Slide 118, Kidney (PASH) locate the parietal layer of Bowman’s capsule surrounding the glomeruli (blood capillaries). Identify the layer of simple squamous epithelium which forms the parietal layer of Bowman’s capsule. These cells rest on a pink-staining basement membrane. Note that you can see only the nuclei clearly; the attenuated cytoplasm is indistinct.
b. On slide 18, Spleen (H&E), locate the connective tissue capsule that covers the spleen and note the simple squamous epithelium covering the capsule. This lining is called the mesothelium. A mesothelium is defined as a single layer of flattened cells forming an epithelium that lines serous (body) cavities. Note the shapes of the cells. In some regions, they may appear to be slightly cuboidal.
2. Simple cuboidal. The height of each component cell is approximately equivalent to its width.
a. On slide 114, Kidney (H&E), locate segments of kidney tubules lined with simple cuboidal epithelium. In this type of epithelium the nucleus is round and located in the center of the cell. Other segments of a kidney tubule may be lined by epithelial cells ranging from simple squamous to low columnar or pyramidal (modified columnar) in shape. On slide 118, Kidney (PASH) note how well the PAS stain demonstrates the basement membranes underlying the various epithelial. Cells of different heights are also readily observed on this slide.
3. Simple columnar. The height exceeds the width of the cell.
a. On slide 140, duodenum, (PASH), observe the layer of columnar cells that cover the villi. The ovoid nuclei are located in the lower one-half of the cells. Study the shapes of the cells, the location of the nuclei and the specialization of the free surface. These columnar cells are absorptive cells that have microvilli forming a striated border and covered by a PAS-positive glycocalyx. Goblet cells, which are columnar cells modified to secrete mucus, can be seen interspersed among the absorptive columnar epithelial cells. The goblets in these cells exhibit heavy PAS staining.
4. Pseudostratified. In this type of simple epithelium the nuclei of the cells appear in irregular layers and may give the false impression that the cells themselves are stratified. In a pseudostratified epithelium all the cells reach the basement membrane even though the nuclei lie at different levels in the tissue. Only the tall cells, however, reach the free surface.
a. On slide 2, Trachea (H&E), identify the pseudostratified columnar ciliated epithelium which lines the lumen of the trachea. Find an area where the epithelium is intact; it is torn off in places. The epithelium rests on a thick basement membrane. Scattered throughout the epithelium are numerous goblet cells that produce a mucous secretion that traps inspired particles. Study the position of the nuclei. Note once again the cilia of the tall cells of the pseudostratified columnar epithelium.
b. On slide 6, Epididymis (H&E), is a section through the epididymis, a highly coiled genital duct of the male. The cross and oblique sections of this duct are the most numerous of the tubular structures on this slide. Study the pseudostratified columnar epithelium lining the lumen of the epididymis. Goblet cells and cilia are lacking and the basement membrane is not as prominent as it is for the epithelium of the trachea. Tall columnar cells with stereocilia are present. Smaller basal cells can be identified by observing their nuclei that are located close to the basement membrane.