BIOM 121 1nd EditionChapter 23: part 4Lecture 4 (September 2) Small Intestine Major organ of digestion and absorption From pyloric sphincter to ileocecal valve  Subdivision Duodenum (retroperitoneal)- The bile duct and main pancreatic duct Enter at the major duodenal papilla Controlled by the hepatopancreatic sphincter Jejunum Ileum Structural Modifications: increase surface area of proximal part for nutrition absorption Circular folds Villi: fingerlike projections of mucosa lined with simple columnar absorptive cells andGoblet cells Microvilli: projections of absorptive cells; bear brush border enzymes Submucosa Peyer’s Patches protect distal part against bacteria Digestion: Chime from stomach contains: partially digested carbohydrates and proteins and undigested fats Slow delivery of hypertonic chime Delivery of bile, enzymes, & bicarbonate from the liver and pancreas Mixing  Liver Largest gland in the body 4 lobes: right, left, caudate, & quadrate Falciform ligament Separates the larger right and smaller left lobes Suspends liver from the diaphragm and anterior abdominal wall Functions: Hepatocyte - Process blood-borne nutrients- Store fat-soluble vitamins- Perform detoxification- Produce approx. 900 ml bile per day Bile is yellowish, alkaline solution containing: Bile salts: cholesterol derivatives that function in fat emulsification & absorption Bilirubin: pigment formed from heme Cholesterol, neutral fats, phospholipids, & electrolytes Gallbladder Thin-walled muscular sac on the ventral surface of the liver Stores and concentrates bile by absorbing its water and ions Releases bile via the cystic duct, which flows into the bile duct Pancreas Endocrine function Pancreatic islets secrete insulin and glucagon Exocrine function Acini: clusters of secretory cells - Secrete pancreatic juice Zymogen granules of secretory cells contain digestive enzymes Pancreatic juice: watery alkaline solution (pH 8) neutralizes chime Electrolytes - HCO3- Enzymes- Amylase, lipases, nucleases are secreted in active form but require ions or bile foroptimal activity - Proteases secreted in inactive form Protease activation in duodenum- Trypsinogen is activated to trypsin by brush border enzyme enteropeptidase - Procarboxypeptidase and chymotrypsinogen are activated by trypsin Large Intestine Regions: Cecum  Colon Rectum Anal canal Functions:  propulsion of feces toward the anus (major) Vitamins, water, & electrolytes are reclaimed Bacterial Flora Enter from the small intestine or anus- Colonize the colon- Ferment indigestible carbohydrates- Release irritating acids and gases- Synthesize B complex vitamins and vitamin K Haustral contractioms: slow segmenting movements Haustra sequentially contract in response to distension Gastrocolic reflex Initiated by presence of food in the stomach Activates 3-4 slow powerful peristaltic waves per day in the colon (mass movemtns) Rectum: 3 rectal valves stop feces from being passed with gas Anal canal: last segment of the large intestine Sphincters: Internal anal sphincter=smooth muscle External anal sphincter=skeletal