Reading: RR&K, Chapter 4
SLIDE 56c small intestine, rat (toluidine blue)
(RR&K p66, Fig.4.9)
This slide contains a small fragment of the wall of the rat small intestine embedded in plastic. Similar to slides of the small intestine that you studied in the previous laboratory session, this slide shows several villi, which are lined by a simple columnar epithelium with a striated border. Observe the apical surface of the cells near the junction of the striated border with the rest of the epithelial cell. Identify small dark dots at the apical-lateral surfaces between adjacent epithelial cells. These terminal bars are best seen with the oil immersion lens while looking between cells that are cut perpendicular to the basement membrane. The small dots represent sections through the terminal bars. When the cut is parallel to the basement membrane and at the apical surface of the epithelial cells, the terminal bar appears as a dark blue line surrounding the cell. Be sure you can describe the components of the terminal bars that would be visible in transmission electron micrographs (see EM Package: FIGURE 03). Nuclei (with nucleolus, euchromatin, and heterochromatin) are present at the basal portion of the epithelial cells while pale blue mitochondria are usually found near the apical region of these cells. Locate the goblet cells cut longitudinally and in cross-section. The deeply stained secretory product of these unicellular glands makes the goblet cells apparent. Can you find migrating lymphocytes within the epithelium that lines the villi? Observe the extracellular spaces between the absorptive cells. This space reflects the activity of fluid transport across the epithelium and is not an artifact of preparation. How do the terminal bars contribute to the formation of this extracellular space (or compartment)?
Check list for SLIDE 56c:
FIGURE 03 Small intestine, absorptive cell (EM)
(RR&K p93, Fig.1,2)
This electron micrograph represents the apical surface of two absorptive cells of the small intestine. The junctional complex demarcates the borders of these cells. Identify components of a junctional complex. Apical and lateral plasma membranes are visible. Identify the intercellular space between the lateral plasma membranes. The striated border seen at the LM is visualized here as numerous microvilli. Microfilaments (actin) can be seen projecting from each microvillus into a region of the cell void of organelles (i.e., terminal web). The small tubular vesicles beneath the microfilaments are endosomes, since these cells actively transport proteins.
Check list for FIGURE 03:
SLIDE 42c skin fingertip, human (H&E)
(RR&K p392, Fig. 1,3; p 371, Fig. 14.2)
Orient yourself on this slide using the lowest power objective lens and distinguish the epidermis (composed of a stratified squamous keratinized epithelium) from the dermis (composed primarily of connective tissue). Note the progressive changes in appearance (size, shape and staining properties) of cells within the epidermis. Describe how the appearance of these cells reflects the regeneration of this epithelium. Do not memorize the names of the different layers but be aware of what is taking place. In a subsequent laboratory, you will examine the integument in more detail. The skin of the finger is covered with a stratified squamous keratinized epithelium. The dead (lacking nuclei) keratinized cells at the surface (squamous) are flat and serve as a basis for classification of this epithelium as squamous. Underlying the epidermis is the supportive dermis which contains numerous examples of blood vessels and glands (sweat) with their associated ducts. The blood vessels are lined with a simple squamous epithelium (endothelium). Analysis of the epithelium of the glands and ducts is not a simple assignment. Examine the glands and ducts and classify their epithelium. Are the glands uni- or multi-cellular? Can you find the sweat ducts in the keratinized layer of the epidermis?
Check list for SLIDE 42c: 
SLIDE 77b monkey, urinary bladder (H&E)
(RR&K p594, Fig. 1,2,3)
This section of the monkey bladder is embedded in plastic. With the reversed ocular, identify the epithelium that lines the lumen of the bladder. At high power, study the large surface cells. Compare dome-shaped cells with more flattened cells. These dome-shaped cells occasionally have two nuclei. Compare the size of the surface cells with that of the deep cells. The deep cells are variable in shape. The number of layers of deep cells is variable and depends on the state of distension of the bladder. The nature of the red-stained material seen in many cells is not known. The presence of dark and light cells is probably a preparation artifact. Can you find two examples of simple squamous epithelium on this slide?
Check list for SLIDE 77b: 
SLIDE 42p, skin, carcinoma in situ (human), (H&E)
(RR&K p393, Fig. 1,2,3; p395, Fig. 1,2,3; p397 Fig. 1,2; p399 Fig. 1,2,3; p401, Fig. 1,2,3)
On this slide note two sections of the skin removed from the patient with Bowen's disease, characterized by histological features of squamous cell carcinoma in situ (CIS). Compare the stratified squamous keratinized epithelium (epidermis) of these sections to normal epithelium as seen in SLIDE 42c. Identify areas of the stratified squamous epithelium whereby cellular morphology as well as the cellular organization is atypical. Note that in some areas you will observe nuclei of cells in the top layer of the epithelium (parakeratosis). Finally, mitotic cells can be found above the basal layer of cells. Observe the basement membrane. Do you see any proliferation of the cancer cells into the underlaying connective tissue? Deep to the basement membrane you will observe a moderate to heavy infiltration of lymphocytes (connective tissue cells).
Check list for SLIDE 42p:
1. Identify and describe the structure and function(s) of the various types of epithelia.
2. How do apical and basolateral surfaces of epithelial cells differ from each other?
3. Discuss reasons why organelles are frequently polarized within epithelial cells.
4. Describe the structure and function of each of the components of a junctional complex. What is a terminal bar?
5. Describe the structure and function of a gap junction.
6. Which cells are the oldest in a stratified squamous keratinized epithelium?
7. By what methods can the basement membrane be visualized with the light microscope? Describe its composition and how it appears in the electron microscope.
8. Which element of the epithelium is the most important for a pathologist to make a diagnosis of carcinoma in situ?
This unit is a continuation of the previous (Epithelium I), with further information on epithelial structures.