2010 GI 2 complete +lab (1) - GASTROINTESTINAL SYSTEM II....

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GASTROINTESTINAL SYSTEM II. Small Intestine, Large Intestine, Appendix, Anal Canal. Barry R. J. Rittman, Ph.D. Reading: Gartner and Hiatt Chapter 14, p277; Junqueira and Carneiro Chapter 15, p281; Sheedlo Chapter 14, p139 - Learning Objectives: 1. Name the cell types found in the epithelium of small and large intestines and their functions. 2. Describe villous structure with regard to epithelium, lymphatics and blood supply. 3. List the features and functions of Peyer's patches. 4. List functions of the small intestinal epithelium. 5. Correlate unique structural features throughout the small and large intestines with their functional significance for that zone. 6. Describe how the appendix can be distinguished histologically from the colon. 7. List unique features of the rectum and anal canal not found elsewhere in the GI tract. Key Words: Villi, microvilli, crypts, Paneth cells, absorptive cells, Payer’s patches, Brunner's glands, Auerbach's and Meissner's plexus. THE SMALL INTESTINE. I. GENERAL FEATURES. A. A tube approximately 5-7 meters long. Ridges of mucosa plus associated submucosa. Villi, are small (up to 1.5 mm long) epithelium-covered, finger like projections of the Plicae circulares (valves of Kerckring) are permanent folds created by great rolling mounds of submucosa. Plica circulares and villi significantly increase the luminal surface area. B. Small intestine continues digestion of chyme from stomach using enzymes associated with the glycocalyx, pancreatic enzymes and liver bile and absorbs the resulting nutrients. Lubrication and peristalsis to facilitate moving of contents. C. There are three portions duodenum, jejunum and ileum – all have the same basic histologic appearance (with minor differences) but some differences in function. 1
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The 4 basic layers are shown above page 285 lI. Tunica Mucosa - General Architecture Typical GI tract pattern of epithelium, lamina propria and muscularis mucosa. Finger-like villi extend into the lumen and pocket-like crypts of Lieberkϋhn extend from the surface down into the lamina propria. Both are lined by a continuous layer of simple columnar cells. A central lacteal in the lamina propria of each villus drains into lymphatic vessels in the submucosa as seen in the diagram below. Lacteals are very important for draining chylomicrons that are absorbed by the epithelium. After a high fat meal, the splanchnic lymphatic bed will turn white due to the appearance of large amounts of these small fatty globules. 2
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A dense capillary plexus is immediately under the epithelium so that absorbed molecules have only very short distances to travel through the lamina propria to be taken up into the vasculature. Capillaries arise from one or two arterioles in the center of each villus and these in turn arise from sub mucosal arteries. Capillaries drain into one or two central venules that flow into submucosal veins.
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This note was uploaded on 12/25/2010 for the course NEUROBIOLO MSI taught by Professor Rogerj.bick during the Spring '10 term at University of Texas Health Science Center at San Antonio.

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2010 GI 2 complete +lab (1) - GASTROINTESTINAL SYSTEM II....

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