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NORTH BIOL& 242 - Chapter 23­ Digestive System, Part 2

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Ch 23- Digestive System, Part 2Junction of stomach and small intestineSmall IntestineLayers of the small intestineSlide 5Plica and villiVillus and enzymes of the brush border cellsRegional Features of the Small IntestineDuodenumJejunum- PanoramaIleumWhat organs secrete into the small intestine?Anatomy of the pancreasPancreasSlide 15Enzymes produced by the pancreasProteolytic EnzymesSlide 18LiverHepatic Portal SystemSlide 21Slide 22Liver lobulesLiver lobules- Portal TriadsMajor functions of the liverMetabolic RegulationMetabolic regulationWhat role does the liver play in amino acid metabolism?What role does the liver play in lipid metabolism?What role does the liver play in carbohydrate metabolism?Other metabolic functions of the liverHematological regulationHepatocytes produce bileWhat is bile?Gall BladderWhat regulates release of bile?Review of Digestion at Small IntestineThe last part..large intestineAnatomy of the large intestineHistology of the Large IntestineSlide 41Chemical Digestion and AbsorptionSlide 43Recall polymers and monomersHydrolysisAbsorptionCarbohydratesWhere do we find these three enzymes?Disaccharides in intestinal lumen interact with brush border enzymes, and the enzymatic products are absorbedWhen brush border epithelial cells fail to make lactase….Absorption of CarbsCo-transportAbsorbed nutrients can enter a capillary or a lactealProtein DigestionSlide 55Absorption of proteinsDigestion of lipidsLipid Digestion and AbsorptionChylomicronsVitamin absorptionIon AbsorptionIon and Vitamin AbsorptionWater AbsorptionCh 23- Digestive System, Part 2• Small intestine• Pancreas• Liver -Hepatic portal system• Gall bladder -Bile • Large Intestine• Chemical digestion and absorptionJunction of stomach and small intestineSmall Intestine•Major function- responsible for 90% of absorption and also important for digestion•Divided into three regions–Duodenum- ‘mixing bowl’–Jejunum- chemical digestion/absorption–Ileum- protection from large intestineLayers of the small intestinePlicaUnique to the small intestine is the presence of plica (plicae circulares). Plica are permanent folds of the mucosa and submucosa.On the plica, you will see villi--Present only in small intestine-Crypts spaced between them-Do not confuse with ‘mircovilli’One plicaOne villusPlica and villiEach plica supports a forest of villi. Each villus is covered with simple columnar epithelium. These epithelial cells have microvilli. Phew!Villus and enzymes of the brush border cellsmicrovilliBrush border cellThe lamina propria of each villus contains a lacteal, nerves and blood vesselsRegional Features of the Small Intestine •Duodenum- site of chyme entry, where it is blasted with HCO3- (and other things)–Along duodenum, pH of chyme changes from 1-2 to 7-8–Mucus glands of mucosa–Also, Brunner’s glands (submucosal glands) •Jejunum- first half has numerous plicae and villi, but they decrease in number en route to ileum–Brush border enzymes•Ileum - lack plicae, contain masses of lymphoid tissue..why??DuodenumPlicaVilliCryptsBrunner’s Glands (submucosal glands)Jejunum- PanoramaIleumCryptsGoblet CellsPeyer’s PatchesWhat organs secrete into the small intestine? Gall bladderLiverAnatomy of the pancreas-An accessory structure of the small intestinePancreas•Where have you seen the pancreas before? •Primarily an exocrine gland (99% of cells)•Composed of a series of ductules that are surrounded by secretory cells, acinar cells• Cuboidal epithelial cells that form pancreatic acini • Pancreatic juice produced by acinar cells• Alkaline mixture of enzymes, water, and ions• Over 1200 ml of ‘juice’ produced each day!• Travels in pancreatic duct, joins the common bile ductAcinar CellsEnzymes produced by the pancreas•Pancreatic alpha-amylase•Pancreatic lipase•Nucleases•Four inactive proteolytic enzymes–Not activated until they reach the small intestineProteolytic Enzymes•Inactive trypsinogen converted to active trypsin by enteropeptidase (enterokinase)•Trypsin then converts other proenzymes into their active forms–Chymotrypsin–Carboxypeptidase1234trypsinogenenteropeptidaseTrypsin is now active, and will activate other proteases: ChymotrypsinCarboxypeptidaseBrush border cells56Inactive protease  active proteaseInactive proteases released from acinar cellsLiver•Largest visceral organ, 3 lb•Surrounded by fibrous capsule•Has numerous lobes, with numerous lobules–Cells are called hepatocyes•Receives ~25% of total cardiac output!!•Blood flow to and from the liver is uniqueHepatic Portal System• Liver receives 1/3 of blood via hepatic artery (not shown)• 2/3 from hepatic portal vein• This major vein drains capillaries from: esophagus, stomach, small and large intestine and THEN heads to liver•Venous blood from liver dumps directly into inferior vena cava Any guesses as to a major function of the liver?Hepatic Portal System-The portal venous blood contains all of the products of digestion absorbed from the GI tract. -Thus all nutrients are processed/viewed in the liver (by hepatocytes) before being released back into the central veins.Liver•Each lobe divided into lobules•Cells of the liver are hepatocytes–Arranged as a single layer of cells, stacked–Divided by sinusoids–Blood flows through sinusoids, past Kupffer cells (resident macrophage)KupfferRBCsbacteriaLiver lobulesHepatocytes arranged into ‘walls’. Walls radiate outward from a central point. The central area contains a single, central vein. Blood is flowing towards centerLiver lobules- Portal TriadsCentral VeinPortal Triad1 mmMajor functions of the liver•Metabolic regulation•Hematological regulation•Bile production (its only true digestive function)Metabolic Regulation•Hepatocytes regulate the composition of the blood and blood nutrients•They do this by selectively secreting and absorbing molecules from the blood•What molecules? Carbs, lipids, amino acids, waste products, vitamins, minerals and drugsPortal triadMetabolic regulation•Hepatocytes adjust the contents of the blood by selective absorption and secretion–Remove/store excess nutrients–Correct deficiencies•Hepatocytes are able to take in and/or release large molecules with ease, partly because the nearby capillaries are so leaky!hepatocytesA big ol’ leaky capillary, a sinusoidal capillaryWhat role does the liver play in amino acid metabolism?•Removes excess


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NORTH BIOL& 242 - Chapter 23­ Digestive System, Part 2

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