Reading: RR&K Chapter 16
SLIDE 55e stomach, fundus, monkey (H&E)
(RR&K p479, Fig. 1,23; p481 Fig. 1,2,3,4)
This section was taken from the body of the stomach and shows the fundic glands. Identify the mucosa, submucosa, muscularis externa and serosa.
The mucosa consists of gastric pits and glands and the muscularis mucosae. The surface epithelium and gastric pits consist of closely packed surface mucous cells. Note the large pale region in the apex of surface mucous cells which normally contains mucous droplets. The glands contain mucous neck cells, parietal cells, and Chief cells. The parietal cells closest to the lumen of the stomach mark the beginning of the isthmus of the gland. Their nuclei are large and spherical in shape (some cells are binucleate) with a pink cytoplasm. What is the function of the parietal cells? The mucous neck cells are ill-defined in shape, having been squeezed between the parietal cells. Their nuclei are elongated and interspersed among the parietal cells. (These cells are hard to identify, so don't worry if you have difficulty finding them). The Chief cells are secretory with abundant ergastoplasm. These basophilic cells can be found at the base of the glands adjacent to the muscularis mucosae. Vacuoles in the cytoplasm probably contained secretory granules. What is the function of the chief cells? The lamina propria between the glands is very cellular. Strands of smooth muscle extending from the muscularis mucosae towards the surface can be identified. The two layers of the muscularis mucosae are not always clearly defined.
The submucosa contains large blood vessels and occasional Meissner's plexus. The muscularis externa is made up of 2-3 layers of smooth muscle. Identify the ganglion cells of the Auerbach's plexus. The serosa consists of a mesothelium and underlying connective tissue.
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FIGURE 04 stomach, fundus, chief cell (EM)
(RR&K p448, Fig. 16,7)
This electron micrograph shows profiles of four Chief cells. These cells contain numerous heterogenous secretory vesicles near their apical surfaces. In addition, abundant rough endoplasmic reticulum can be found near the basal surfaces of these cells. Mitochondria and Golgi apparatus are also evident. Locate the basal lamina and the junctional complexes.
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SLIDE 55d stomach, pylorus, monkey (H&E)
(RR&K p483, Fig. 1,2,3)
This section was taken from the pyloric region of the stomach and shows a well preserved mucosa and a thick muscularis externa which forms the pyloric sphincter. With the reversed ocular locate the mucosa, submucosa, muscularis externa and serosa.
The mucosa consists of gastric pits and glands, but the epithelial cells are different than those seen in the fundic region of stomach. The surface mucous cells are columnar cells with round nuclei and abundant mucin. Compare the morphology of the fully differentiated surface mucous cells with the less differentiated cells within the pits and neck of the glands. The glands are made of mucous gland cells, parietal cells, and APUD cells. Mucous gland cells can be easily identified by their flattened nuclei and abundant mucin. The parietal cells are poorly stained cell with a large round nucleus and a free apical surface. The entero-endocrine (APUD) cells do not stain at all. Its condensed nucleus is surrounded by a small amount of cytoplasm. These cells are smaller than the parietal cells. APUD cells are located on the basal lamina of the gland, usually near a blood vessel and do not reach the luminal surface. The lamina propria consists of many connective tissue cells (e.g., eosinophils and plasma cells) and smooth muscle cells. Examine the inner circular and outer longitudinal layer of muscularis mucosa.
The submucosa contains large blood vessels, adipocytes, and occasional Meissner's plexus. Identify mast cells near the blood vessels in the submucosa. The muscularis externa is made up of 2-3 layers of smooth muscle. Notice the change in thickness of the muscularis externa on this slide. As you move toward the pyloric sphincter the muscle layers become very thick. Identify the ganglion cells of the myenteric (Auerbach's) plexus. The serosa consists of a mesothelium and underlying connective tissue.
Check list for SLIDE 55d:
SLIDE 56n duodenum, rabbit (H&E)
(RR&K p485, Fig. 1,2)
Locate the mucosa, submucosa, muscularis externa and serosa. The mucosa and submucosa of the duodenum forms circular folds known as plica circularis. Note that the muscularis externa does not extend into the folds.
The mucosa consists of villi, glands, and the muscularis mucosae. The villi extend as numerous small elongated finger-like projections into the lumen. The epithelial surface of these villi consists of enterocytes and goblet cells. An occasional migrating lymphocyte may also be found within the epithelium. The glands of the mucous membrane are the crypts of Lieberkhhn which dip down from the luminal surface of the duodenum to the level of muscularis mucosae. The highly cellular lamina propria makes up the core of the villi. Identify those connective tissue cells and smooth muscle cells present in lamina propria.
The submucosa of the duodenum contains mucous-secreting glands located in the submucosa (Brunner's glands). Observe the pale-staining Brunner's gland separated from the lamina propria by the eosinophilic muscularis mucosa. The presence of these submucosal glands distinguishes the duodenum from other regions of the small intestine. Alkaline secretions from these glands are needed in the first part of the small intestine to help neutralize the highly acidic contents of the stomach as they pass into the intestine. The muscularis externa includes an inner circular and outer longitudinal layers of smooth muscle. Identify the ganglion cells of the Auerbach's plexus.
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SLIDE 56i small intestine, rat (H&E)
(RR&K p487, Fig. 1,2,3)
Locate the mucosa, submucosa, muscularis externa, and serosa or adventitia (seen in Version 2). The mucosa consists of villi, glands, and muscularis mucosae. The villi and glands are lined by a simple columnar epithelium. Absorptive and goblet cells are found in the epithelial lining of the lumen. The expanded apical part of the goblet cells contains numerous pale granules which correspond to droplets of mucinogen. Identify the striated border of the absorptive cells. Inside the crypts of Lieberkhhn, identify goblet cells, mitotic cells, and Paneth cells (containing large eosinophilic secretory granules). The Paneth cells are better seen in Version 1 of this slide. A highly cellular lamina propria makes up the core of the villi. Note the distribution of smooth muscle, capillary networks, lacteals, and connective tissue cells. The muscularis mucosae separates the mucosa from the submucosa. Identify muscularis mucosae and submucosa.
Submucosa contains large accumulations of lymphatic tissue, blood vessels, and parasympathetic ganglion cells of the submucosal nerve plexus (Meissner's plexus). Try to identify various vessels in this region. In the muscularis externa identify nerves and the ganglion cells of Auerbach's plexus.
Serosa consists of a mesothelium and a thin layer of connective tissue subjacent to the basement membrane. The adventitia seen in Version 2 is connective tissue, without a mesothelium, that is continuous with the connective tissue surrounding neighboring organs.
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SLIDE 58a colon, human (H&E)
(RR&K p491, Fig. 1,2,3,4)
The wall of the colon is structurally similar to the intestine, with a mucosa, submucosa, muscularis externa, and serosa. Find the luminal surface, which is in striking contrast with the surface of small intestine.
Unlike the small intestine, the colon mucosa consists of only glands. Note the numerous cross-sectional profiles of the glands. No villi are present. The lining epithelium contains mainly goblet cells, a few enterocytes, and migrating lymphocytes. Paneth cells are noticeably absent from the crypts. Review and compare the epithelial lining of the surface with that in the crypts. Note the organization of the lamina propria, muscularis mucosa and aggregates of gut-associated lymphatic tissue (GALT). How many layers of the muscularis mucosae can you see? The submucosa contains numerous large blood vessels. Can you find a Meissner's plexus? The muscularis externa has two layers of smooth muscle. Find the circular and longitudinal layers of smooth muscle and elements of Auerbach's plexus. Identify the teniae coli, an enlargement of the outer longitudinal layer of muscularis externa. You may observe some mucosal folds (semilunar folds) on your slides. How can you explain this observation?
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SLIDE 59a anorectal junction, monkey (H&E)
(RR&K p495, Fig. 1,2,3)
This is a section of the rectum, anal canal, and anal skin. The walls of the rectum and the anal canal are similar to that seen in the colon and consists of a mucosa, submucosa, muscularis externa and serosa or adventitia. Examine the epithelial changes from simple columnar in the upper anal canal, to nonkeratinized stratified squamous in the distal anal canal, to the keratinized stratified squamous keratinized of the anal skin. Anal transitional zone (ATZ) is located on the level of pectinate line in the anal canal. Histologically, ATZ can be defined as the area interposed between uninterrupted rectal mucosa (simple columnar epithelium) and uninterrupted squamous epithelium. Moving from the non-keratinized stratified squamous epithelium in the anal canal to the keratinized stratified squamous epithelium around perianal skin, you should note the change that occurs associated with the keratinization process. The muscularis mucosae is difficult to see in most areas due to poor preservation and staining. The submucosa is continuous with the dermis of the skin. Examine the musculature of the anal canal wall. Note the presence of both smooth and striated muscle. Unfortunately some of the muscle on this slide is poorly preserved but by comparing a bundle of muscle in different locations you should be able to distinguish between smooth and striated muscle. A thickening of the inner circular layer of the muscularis externa constitutes the internal anal sphincter muscle. Identify the skeletal muscle deep to the muscularis externa. This muscle is the external anal sphincter muscle and probably part of the levator ani muscle. Some of the slides show a small portion of the anal glands. These glands are an example of apocrine sweat glands. Identify the numerous nerves deep to the muscularis externa. There is no serosa on this slide.
Check list for SLIDE 59a: 
The stomach and small intestine are essential in the enzymatic breakdown of food into useful subunits. The small intestine and large intestine serve the function of absorption of nutrients and water. This unit examines the structural aspects of these organs.