| Lab 20 Small & Large Intestines: 1) Index 2) Things to Identify 3) Duodenum 4)Jejunum 5) Ileum 6) Appendix 7) Colon 8) Rectum 9) Rectal Anal Junction 10) Anus 11)Comparison of Structures 12)Practical |
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Duodenum
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# 116 - Duodenum, human, h-e, 1.5mm # 115 - Duodenum, upper portion, monkey, h - e If needed, see # 215 - Duodenum, jejunum, and ileum combination, c.s. |
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Three features appear at the level of the duodenum: 1) goblet cells, 2) submucosal Brunner's glands and 3) plicae circulares (spiral folds formed by the submucosa and mucosa that are also called the valves of Kerckring. Identify these features of the duodenum. Choose one large leaf-like fold or plica for examination at higher power and identify the projections (villi) of the mucosa. Each finger-like villus contain a core of lamina propria gloved by an epithelium composed of columnar cells (enterocytes) and goblet cells. You should be able to distinguish the striated border (microvilli). Of what is the terminal web of these epithelial cells composed and what is the function of the terminal web? There may be lymphocytic infiltrates in the lamina propria of these villi. The lower part of the mucosa is occupied by the intestinal glands (crypts of Lieberkuhn). You will see numerous mitotic figures in these glands and may see Paneth cells in the base of the glands. Isolated APUD (enteroendocrine cells) appear as clear cells in the base of the crypts. Their nuclei are apically located and their wide cytoplasmic base rests on the basement membrane. Adherent to the wall of the duodenum is another digestive organ. Identify it. REFERENCES: Gartner, p. 287, Fig. 1 -3 Ross, pp. 454 - 455, 484 - 485 Wheater, p. 259, Fig. 14.15 - 14.16 DiFiore, p. 197, Fig. 13-1 |
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This is a low power image of the first part of the Small Intestines, the Duodenum. It also has the basic layers of the GI system like the Mucosa, (blue arrows) , Submucosa, (red arrows), and the Muscularis Externa (green arrows). The small intestines has many adaptations to increase it's surface area a. First it has Plicae Circulares (valves of kerckring),which are extensions of the submucosa, indicated by the yellow arrow. The next adaptation is the Villi, which are extensions of the mucosa indicated by the black arrows. Of important identification clues about the duodenum is the presence of Brunner's Glands which are very abundant in the submucosa. No other part of the intestines has these glands so once you see these you can be sure you are looking at the duodenum. Blue arrows - Mucosa Red arrows - Submucosa Green arrow - Muscularis Externa Yellow arrow - Plicae Circulares Black arrows - Intestinal Villi Here is another look at the duodenum. The red arrows are again pointing out the Villi, which are extensions of the mucosa. Of importance is the presence of these light staining glands in the submucosa, Brunner's Glands, which the blue arrows are pointing to. These function to neutralize the acids of the stomach as digested food is passed from the stomach to the duodenum. Can you notice the circular profiles at the base of the villi? These are the Crypts of Lieberkuhn (yellow arrows), here you will find other specialized cells when you look at a higher magnification. Red arrow - Villi Blue arrow - Brunner's Glands Yellow arrows - Crypts of Lieberkuhn
This is a high power shot on the epithelium of one of the Villi. You can see that it is a simple columnar epithelium. These cells that are simple columnar (red arrows) are called Enterocytes and are the absorptive cells of the intestine. On them is the third adaptation to increase surface area which are the Microvilli or Brush border, indicated by the black arrows. The blue arrow is pointing to the other cell present in the intestinal epithelium called Goblet cells. These secrete a mucous secretion to lubricate the digested food as it passes along the intestines. It is important to know that the number of goblet cells INCREASE AS YOU MOVE DOWN THE INTESTINES. So the least amount of goblet cells is found in the duodenum, which can be another clue to help you identify the duodenum. Black arrows - Microvilli Red arrows - Enterocytes Blue arrow - Goblet Cell
This is a close up of one of the duodenal Crypts of Lieberkuhn. The green arrow is pointing to the already familiar Goblet Cells. The blue arrows are pointing to a what are known as Entero-Endocrine cells (APUD Cells). These function to produce and release hormones to effect the GI activity. They can be identified because of the fact that their cytoplasm is relatively light compared to the rest and their nuclei are not in the same plane as the rest of the cells. Can you see how they stand out by their light staining cytoplasm in the image and can you find the one that isn't marked? The red arrow is pointing to another cell type, which is characterized by the presence of RED GRANULES called Paneth Cells. They function to release these red granules, which are full of bacteriocidal lysozymes to prevent possible infections. Green arrows - Goblet Cells Blue arrows - Enteroendocrine Cells Red arrow - Paneth Cell |
Duodenum
Duodenum (villi and brunner's glands)
Goblet cells & Enterocytes
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