Reading: RR&K, Chapters 15 and 16
SLIDE 48b lip, human (H&E)
(RR&K p473, Fig. 1,2,3,4,5,6)
Locate the anterior (facial) and posterior (oral) surfaces of the lip using the reversed ocular. The anterior surface of the lip consists of a thin stratified squamous keratinized epithelium. Beneath the epidermis lies the dermis, which contains hair follicles, sebaceous glands and sweat glands. The labial mucosa is located on the posterior (oral) surface of the lip which is lined by thick stratified squamous epithelium. In the mucosal region of the lip, the outer layer is nonkeratinized and the lamina propria extends deep into the epithelium via numerous papillae. There is an evident lack of stratum granulosum. Note that the lamina propria is highly vascularized.
The red margin of the lip is found between these two regions. Here the epithelium is thin and the blood vessels are very close to the outer surface of the lips. The transition of the epidermis of the skin to the epithelium of the oral mucosa is an example of a mucocutaneous junction and is referred as a wet margin of the lip. Examine the mucocutaneous junction carefully and identify the parakeratinized epithelium. Parakeratinized epithelium shares characteristics of both mucosa and epidermis. The surface cells contain nuclei (as in the mucosa) as well as a keratin-like material (as in the epidermis).
Examine the distribution of striated fibers of orbicularis oris muscle and large blood vessels in the lip.
Check list for SLIDE 48b:
SLIDE 50c tongue, human (H&E)
(RR&K p427, Fig. 1,2; p429, Fig.1,2)
The tongue consists of a specialized mucosa and muscle. The uneven projections at the dorsal surface of the tongue are filiform papillae. The tips of these papillae appear to be broken off. Directly beneath the epithelium is connective tissue. Classify the connective tissue types present. Within the tongue, there are bundles of intrinsic muscles in perpendicular orientations. Classify the muscle type. Examine the histological differences between dense connective tissue and muscle. Also present are large blood vessels and nerves.
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SLIDE 50b tongue, rabbit (H&E)
(RR&K p427, Fig. 1,2; p429, Fig.1,2)
The tongue consists of a specialized mucosa and muscle. The mucosal projections at the dorsal surface of the tongue are filiform and foliate papillae. On the low magnification identify two types of papillae: foliate which occupy the majority of the surface, and filiform on the edge of your section. Observe the well preserved foliate papillae and the sulci between them. Within the epithelium of the sulcus are several taste buds. Directly beneath the epithelium is connective tissue.
Examine the bundles of intrinsic muscles in perpendicular orientations. Classify the muscle type. Examine the histological differences between dense connective tissue and muscle.
Serous (von Ebner's) glands can be found between muscle fibers and in the connective tissue of the mucosa. These glands secrete into ducts that deposit the secretions at the sulcus. The glands on this slide are predominantly serous, but some mucous glands may be present. Serous secreting cells are basophilic (blue ergastoplasm and blue secretory vesicles) with round nuclei. The cytoplasm of a mucus secreting cell is pale blue with its flattened nucleus positioned at the basal surface of the cell. Be careful not to confuse a mucous gland with a duct. Classify the epithelium lining the ducts. Be able to distinguish the ducts from the secretory portions of the glands.
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SLIDE 63e salivary glands (H&E)
(RR&K p431, Fig. 1,2; p433, Fig.1,2; p435, Fig. 1,2)
This slide contains three different specimens. On the left, closest to the label, is the sublingual gland, in the middle is the submandibular gland, and on the right is the parotid gland.
The sublingual gland is predominantly a mucous secreting gland with few serous acini. In H&E staining, many of the acini appear washed out due to a loss of mucin in the slide preparation. The nuclei are flattened due to amount of mucin accumulated in the apical portion of the cell. Some of the mucous acini reveal serous demilunes. Note the grouping of cells containing round nuclei and basophilic cytoplasm in apposition to the mucous acini. These are the serous cells. The acini also contain myoepithelial cells. These specialized cells are within the basement membrane of the acinus and some ducts. The ducts which are found within the lobules of the gland are two types: intercalated and intralobular. Intercalated ducts are very short and thus difficult to find. Their epithelium is either a simple cuboidal or squamous in contrast to the simple columnar of the intralobular duct. The intralobular ducts are the equivalent of the striated ducts of the submandibular and parotid glands. The larger ducts which lead from the lobules are the excretory ducts. These ducts exhibit a stratified appearing epithelium and are surrounded by dense connective tissue.
The submandibular gland is comprised of mostly serous acini and considerably fewer mucous acini. Like the sublingual gland the mucous acini frequently show serous demilunes. Eosinophilic myoepithelial cells are also present in the acini. Intercalated ducts are more readily found in the submandibular gland than in the sublingual gland. They are lined by squamous cells and empty into the striated ducts which are more prominent. Striated ducts have basal striations that can be seen under high magnification. The larger ducts that lead from the lobules, (the excretory ducts), exhibit a stratified-looking epithelium and are either pseudo-stratified or stratified cuboidal. The parotid gland contains only serous acini; however, within the lobules, fat cells are frequently found amongst the serous acini. The nuclei of the serous cells are round and located in the basal region of the cell. The cytoplasm in this area is also highly basophilic, but this staining feature is not very apparent in this specimen. Identify the myoepithelial cells that are present in the acini. The duct system of this gland is essentially similar to that of the submandibular gland (i.e., intercalated, striated, and excretory). Typically, lymphocytes and plasma cells are evident in the connective tissue surrounding the acini and the smaller ducts of the salivary glands. What is the function of these cells?
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SLIDE 54d esophagus, monkey (H&E)
(RR&K p475, Fig. 1,2)
The walls of the organs of the alimentary canal consist of a mucosa, submucosa, muscularis externa, and adventitia (or serosa). This organ is well preserved to demonstrate all four layers.
The mucosa consists of an epithelium (stratified squamous), lamina propria (loose connective tissue) and muscularis mucosae (smooth muscle). Examine the epithelium and note the change of cell shape as you go from the basal to luminal layers. The boundary between the epithelium and lamina propria is quite distinct and is uneven due to numerous connective tissue papillae. In contrast, the boundary between the mucosa and submucosa is marked by the muscularis mucosae, which is the deepest layer of the mucosa. The muscularis mucosae consists of two layers of smooth muscle arranged as an inner circular and outer longitudinal.
The submucosa is a thick layer of fairly dense connective tissue with numerous medium-sized blood vessels. Identify ganglion cells of the submucosal plexus.
The muscularis externa consists of two layers of muscle arranged as an inner circular and outer longitudinal. Identify the types of muscle in each layer and the orientation of the fibers. From what level of the esophagus was each slide made? Can you find nerve fibers and ganglion cells of the myenteric plexus?
The adventitia is a connective tissue layer which blends with the adventitia of the trachea and other surrounding structures. Adipose tissue, large blood vessels and nerves are found here. Occasionally you may find a serosa (mesothelium and underlying connective tissue) adjacent to the adventitia.
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SLIDE 54b esophagus, dog (Masson)
(RR&K p475, Fig. 1,2)
Identify the four layers of the esophageal wall: the mucosa, submucosa, muscularis externa and adventitia. On this slide stained with Masson the identification of the layers appears to be much easier than on the previous H&E slide.
The mucosa consists of the lining epithelium, the lamina propria and the muscularis mucosae. Examine the stratified squamous epithelium and observe the change of cell shape as you go from the basal to luminal layers. The boundary between the epithelium and connective tissue of lamina propria is uneven due to numerous connective tissue papillae. The muscularis mucosae is thick and clearly visible with this stain.
The submucosa is a thick layer of fairly dense connective tissue with numerous tuboalveolar esophageal glands. Identify the glands and the glandular ducts, which pass through the muscularis mucosae and lamina propria to open on the luminal surface of the epithelium. What type of secretions are produced by these glands? Many arteries and veins can be observed in the submucosa. Can you find nerve fibers and ganglion cells of the submucosal plexus?
The muscularis externa consists of two layers of muscle arranged as an inner circular and outer longitudinal. Identify the types of muscle in each layer and the orientation of the fibers. From what level of the esophagus was each slide made? Identify nerve fibers and ganglion cells of the myenteric plexus.
The adventitia is a connective tissue layer which blends with the adventitia of the trachea and other surrounding structures. Adipose tissue, large blood vessels and nerves are found here.
Check list for SLIDE 54b:
The oral cavity and esophagus are specialized for food intake and delivery to the stomach. The oral cavity initiates basic digestion and also allows for taste.