chapter23 digestivepart2marieb

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  • 1. Ch 23: DigestiveSystem, Part 2Objectives:Discuss the general functions andanatomy of the digestive tract,including accessory structures.First, an overview of the tubularnature of the digestive system.Describe the individual organs ofthe system, including adiscussion of the gross andmicroscopic anatomy. Developed byJohn Gallagher, MS, DVM

2. General Organization of aTubular Organ (Repetio est.) 3. The 4 Layers of the Gut (review)1) MucosaEpithelium - usually simple columnar with gobletcells; may be stratified squamous if protection neededLamina propria areolar connective tissue deep toepitheliumMuscularis mucosae -produces folds - plicae (smallintestine) or rugae (stomach)2) Submucosa made up of loose connective tissuecontains submucosal plexus and blood vessels3) Muscularis externa smooth muscle, usually twolayers (controlled by the myenteric plexus; source ofperistalsis ) -inner layer: circularouter layer: longitudinal4) Serosa visceral layer of mesentery (contiguous with the peritoneum) or adventitia depending on location Fig 23.7 4. Regions of Small IntestineSI is longest part of alimentarycanal. Almost all absorption ofnutrients is in SI, with a fewimportant exceptions.1. Duodenum2. Jejunum3. Ileum 5. Regions of Small Intestine1. Duodenum (short, 12 inches) Mostly retroperitoneal fixed shape & position Mixing bowl for chyme & ? Entry of bile duct at the duodenalpapilla 6. Regions of Small Intestine2. Jejunum (2.5 m long) Most of digestion Mostly superior to the ileum 7. Regions of Small Intestine3. Ileum (longest at 3.5 m) Most of absorption, ends in Ileocecal valve slit valve into large intestine (colon) 8. Comparative HistologyNote Bile and Pancreatic Ductsin Duodenum, Duodenal papillaGlandsin Duodenum Mucus pH increase (buffer)Similar histologyPeyers Patches AKA MALT 9. Comparative Histology, contd Specialized CellsAbsorptive cells VeryactiveGoblet cellsEnteroendocrinecells LocalcommunicationN.B. hepatopancreaticsphincter 10. Large Intestine = Large Bowel = Colon =1.5 meters Cecum pocket at proximal end with Vermiform Appendix in LRQ Appendicitis p 669 Ileocecal Valve Opens when stomach is filling Prevents fecal reflux into ileum 11. Large Intestine = Large Bowel = Colon =1.5 meters Ascending colon - on right, between cecum and right colic flexure Transverse colon - horizontal portion Descending colon - left side, between left colic flexure and Sigmoid colon - S bend near terminal end 12. Large intestine, contd1. Mucosa - simple columnar epith with abundant goblet cells; stratified squamous epithelium near anal canal2. No villi3. Longitudinal muscle layerincomplete, forms three bandsor taenia coli4. Circular muscle - forms pocketsor haustra between bands5. Anal Sphincter 13. Rectum and Anus Rectum terminal end is analcanal - ending at the anus - which has internal involuntary sphincter and external voluntary sphincter Retroperitoneal Mucus glands Rectal and Anal valves 14. Blood SupplyCeliac trunk - 3 branches to liver, gallbladder, esophagus, stomach, duodenum, pancreas, and spleenSuperior mesenteric to pancreas and duodenum, small intestine and part of colonInferior mesenteric to colon 15. Colorectal PolypsGenerally benignAsymptomaticMay bleedMay be precancerousVirtualColonoscopy 16. LiverLocated in RUQ, adjacent to the diaphragm, largest organ made up of 4 lobes (left and right, caudate, and quadrate) Falciform ligament (remnant of fetal blood supplyHilus (porta hepatis) "entry" point on thevisceral surface 17. Liver, contdExtremely versatile: Know a few functions?Gall bladder-storage of bileBlood supply: hepatic artery (1/3) and portal vein (2/3); Return via Central V. to vena cava 18. Microscopic anatomy: Liver lobules andportal triads See Fig 23.26100,000 Lobules (the basicfunctional unit)Hepatocytes are arrangedlike spokes in a hexagonalwheelBathedin blood of hepaticsinusoidsFromPortal V. andHepatic A.Triads at each cornerKupffer Cells are phagocytic 19. Gall Bladder Gall Stones Fundus, body, neck Hepatic Duct and Cystic ductconnect to form the CommonBile Duct Enters at the proximalduodenum Storage and Concentration ofBile 20. Pancreas Retroperitoneal Endocrine or exocrine gland? Both! Only 1% is endocrine Insulin, et al. Simple Cuboidal Epith arranged inAcini Digestive enzymes excreted intothe pancreatic duct Common bile duct and pancreaticduct lead to duodenal ampulla andpapilla Controlled by hepatopancreatic sphincter 21. Pancreas, contd Acinar Cells Several types of digestive enzymese.g., trypsin Used as diagnostic tools forpancreatitis Islets of Langerhans AKA pancreatic islets Insulin, other hormones Chapt 25


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