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This 7 page Class Notes was uploaded by Jess Graff on Monday May 2, 2016. The Class Notes belongs to BMS 508 at University of New Hampshire taught by Mary Katherine Lockwood, PhD in Spring 2016. Since its upload, it has received 5 views. For similar materials see Human Anatomy and Physiology II in Biological Sciences at University of New Hampshire.
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Date Created: 05/02/16
BMS 508.03 4/6/2016 Chapter 24 (cont) Digestion & Metabolism (cont) The Stomach • Digestion and Absorption in the Stomach • Stomach performs preliminary digestion of proteins by pepsin • Some digestion of carbohydrates (by salivary amylase) • Lipids (by lingual lipase) • Stomach contents • Become more fluid • pH approaches 2.0 • Pepsin activity increases • Protein disassembly begins • Although digestion occurs in the stomach, nutrients are not absorbed there The Small Intestine • The Duodenum • The segment of small intestine closest to stomach • 25 cm (10 in.) long • “Mixing bowl” that receives chyme from stomach and digestive secretions from pancreas and liver • Functions of the duodenum: • To receive chyme from stomach • To neutralize acids before they can damage the absorptive surfaces of the small intestine • The Jejunum • The middle segment of small intestine • 2.5 meters (8.2 ft) long • The location of most: • Chemical digestion • Nutrient absorption • Has few plicae circulares • Small villi • The Ileum • The final segment of small intestine • 3.5 meters (11.48 ft) long • Ends at the ileocecal valve • A sphincter that controls flow of material from the ileum into the cecum of the large intestine • Histology of the Small Intestine • Circular folds (plicae circulares) • Transverse folds in intestinal lining • Are permanent features • Do not disappear when small intestine fills • Intestinal villi • A series of fingerlike projections in mucosa of small intestine • Covered by simple columnar epithelium • Covered with microvilli • Intestinal glands (Crypts of Lieberkühn) • Mucous cells between columnar epithelial cells • Eject mucins onto intestinal surfaces • Openings from intestinal glands • To intestinal lumen at bases of villi • Entrances for brush border enzymes • Intestinal Glands • Brush border enzymes • Integral membrane proteins • On surfaces of intestinal microvilli • Break down materials in contact with brush border • Enteropeptidase • A brush border enzyme • Activates pancreatic proenzyme trypsinogen • Enteroendocrine cells • Produce intestinal hormones such as gastrin, cholecystokinin, and secretin • Duodenal glands • Also called submucosal glands or Brunner’s glands • Produce copious quantities of mucus • When chyme arrives from stomach • Intestinal Secretions • Watery intestinal juice • 1.8 liters per day enter intestinal lumen • Moisten chyme • Assist in buffering acids • Keep digestive enzymes and products of digestion in solution • Intestinal Movements • Chyme arrives in duodenum • Weak peristaltic contractions move it slowly toward jejunum • Myenteric reflexes • Not under CNS control • Parasympathetic stimulation accelerates local peristalsis and segmentation • The Gastroenteric Reflex • Stimulates motility and secretion • Along entire small intestine • The Gastroileal Reflex • Triggers relaxation of ileocecal valve • Allows materials to pass from small intestine into large intestine The Pancreas • The Pancreas • Lies posterior to stomach • From duodenum toward spleen • Bound to posterior wall of abdominal cavity • Wrapped in thin, connective tissue capsule • Regions of the Pancreas • Head • Broad • In loop of duodenum • Body • Slender • Extends toward spleen • Tail • Short and rounded • Histological Organization • Lobules of the pancreas • Separated by connective tissue partitions (septa) • Contain blood vessels and tributaries of pancreatic ducts • In each lobule: • Ducts branch repeatedly • End in blind pockets (pancreatic acini) • Pancreatic acini • Blind pockets • Lined with simple cuboidal epithelium • Contain scattered pancreatic islets • Pancreatic islets • Endocrine tissues of pancreas • Scattered (1% of pancreatic cells) • Functions of the Pancreas • Endocrine cells of the pancreatic islets • Secrete insulin and glucagon into bloodstream • Exocrine cells • Acinar cells and epithelial cells of duct system secrete pancreatic juice • Physiology of the Pancreas • 1000 mL (1 qt) pancreatic juice per day • Controlled by hormones from duodenum • Contain pancreatic enzymes • Pancreatic Enzymes • Include: • Pancreatic alpha-amylase • Pancreatic lipase • Nucleases • Proteolytic enzymes • Pancreatic Alpha-Amylase • A carbohydrase • Breaks down starches • Similar to salivary amylase • Pancreatic Lipase • Breaks down complex lipids • Releases products (e.g., fatty acids) that are easily absorbed • Nucleases • Break down nucleic acids • Proteolytic Enzymes • Break certain proteins apart • Proteases break large protein complexes • Peptidases break small peptides into amino acids • 70% of all pancreatic enzyme production • Secreted as inactive proenzymes • Activated after reaching small intestine The Liver • The Liver • Is the largest visceral organ (1.5 kg; 3.3 lb) • Lies in right hypochondriac and epigastric regions • Extends to left hypochondriac and umbilical regions • Performs essential metabolic and synthetic functions • Anatomy of the Liver • Wrapped in tough fibrous capsule • Covered by visceral peritoneum • Divided into lobes • Hepatic Blood Supply • 1/3 of blood supply • Arterial blood from hepatic artery proper • 2/3 venous blood from hepatic portal vein, originating at: • Esophagus • Stomach • Small intestine • Most of large intestine • Histological Organization of the Liver • Liver lobules • The basic functional units of the liver • Each lobe is divided by connective tissue • About 100,000 liver lobules • 1 mm diameter each • Hexagonal in cross section • With six portal areas (portal triads) • 1 at each corner of lobule • A Portal Area • Contains three structures • Branch of hepatic portal vein • Branch of hepatic artery proper • Small branch of bile duct • Hepatocytes • Adjust circulating levels of nutrients • Through selective absorption and secretion • In a liver lobule form a series of irregular plates arranged like wheel spokes
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