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Chapter 25 - 3 The Digestive System The Gall bladder LaPointe Spring ‘12 Slide #2 • Hollow, pear-shaped organ • Stores, modifies and concentrates bile • Contraction of the gall bladder and release of bile is controlled by CCK and vagal stimulation • Empties into the Cystic duct • Gall stones The Gallbladder LaPointe Spring ‘12 Slide #3 Bile LaPointe Spring ‘12 Slide #4 • Made of water, billirubin, ions, cholesterol, other lipids • Acts as an emulsifier to aid lipid digestion • 90% is reabsorbed in the ileum - enterohepatic circulation of bile Functions of the large intestine LaPointe Spring ‘12 Slide #5 • Reabsorb water and compact material into feces • 1500 mL chyme enter the cecum, 90% of volume reabsorbed yielding 80-150 mL of feces • Absorb vitamins produced by bacteria • Store fecal matter prior to defecation General anatomy of the large intestine • Lies inferior to the stomach • Frames the small intestine • Parts of the large intestine • Cecum • Colon • Ascending • Transverse • Descending • Sigmoid • Rectum • Anal canal LaPointe Spring ‘12 Slide #6 The Large Intestine LaPointe Spring ‘12 Slide #7 Cecum and Rectum LaPointe Spring ‘12 Slide #8 • Cecum • opening protected by ileocecal valve • veriform appendix • Rectum • Last portion of the digestive tract • Terminates at the anal canal • Internal anal sphincter - involuntary smooth muscle • External anal sphincter - voluntary muscle • Hemorrhoids -inflamed veins Rectum LaPointe Spring ‘12 Slide #9 Histology of the large intestine LaPointe Spring ‘12 Slide #10 • Columnar cells except the rectum and anal canal (stratified squamous) • Muscularis externa • circular muscle • only 3 bands longitudinal smooth muscle - taeniae coli • Absence of villi • Presence of goblet cells • Deep intestinal glands Physiology of the large intestine LaPointe Spring ‘12 Slide #11 • Absorption in the large intestine includes: • Water • Vitamins – K, biotin, and B5 • Organic wastes – urobilinogens and sterobilinogens • Bile salts • Some ammonia and other toxins • Mass movements of material through colon and rectum • Defecation reflex triggered by distention of rectal walls Movement in Large Intestine LaPointe Spring ‘12 Slide #12 • Mass movements • Common after meals • Integrated by the enteric plexus • Local reflexes • instigated by the presence of food in the stomach and duodenum • Gastrocolic reflex: initiated by stomach • Duodenocolic reflex: initiated by duodenum Long reflexes of defecation LaPointe Spring ‘12 Slide #13 Coordination secretion and absorption LaPointe Spring ‘12 Slide #14 • Neural and hormonal mechanisms coordinate glands • GI activity stimulated by parasympathetic innervation • Inhibited by sympathetic innervation • Enterogastric, gastroenteric and gastroileal reflexes coordinate stomach and intestines • Several hormones alter motility and secretion Summary Hormone Table GIP duodenum fats, carbohydrates LaPointe Spring ‘12 Slide #15 stim pancreas insulin secretion, inhibits stomach, stim adipose glucose and FA uptake & lipogenesis Marieb Table 23.1.1 Summary Hormone Table (continued) LaPointe Spring ‘12 Slide #16 Marieb Table 23.1.1 Activities of Major Digestive Tract Hormones LaPointe Spring ‘12 Slide #17 From Martini Figure 24.22 Digestion, Absorption, Transport LaPointe Spring ‘12 Slide #18 • Digestion • Disassembles organic food into smaller fragments • Mechanical: breaks large food particles to small • Chemical: breaking of covalent bonds by digestive enzymes • Hydrolyzes carbohydrates, proteins, lipids and nucleic acids for absorption • Absorption and transport • Molecules are moved out of digestive tract and into circulation for distribution throughout body Carbohydrate digestion and absorption LaPointe Spring ‘12 Slide #19 • Begins in the mouth (salivary amylase) completed in small intestine • Salivary and pancreatic amylase • Convert starches to disaccharides, trisaccharides, monosaccharides • Brush border enzymes • Make monosaccharides from disaccharides • maltase (glucose / glucose) • sucrase (glucose / fructose) • lactase (glucose / galactose) • Absorption of monosaccharides occurs across the intestinal epithelia by facilitaed diffusion or Na+ linked cotransporters Lipid digestion and absorption LaPointe Spring ‘12 Slide #20 • Begins in stomach (minor) completed in small intestine • Lipid digestion utilizes lingual and pancreatic lipases converts triglycerides to monoglycerides • Bile salts improve chemical digestion by emulsifying lipid drops • Lipid-bile salt complexes called micelles are formed • Micelles diffuse into intestinal epithelia which resynthesis triglycerides and then release lipids into the circulation as chylomicrons - mixtures of phopholipids and proteins • carried by lymphatic system Lipid Absorption also (see Saladin fig 25.30) LaPointe Spring ‘12 Slide #21 from Seeley, Stephens and Tate Protein digestion and absorption LaPointe Spring ‘12 Slide #22 (See Saladin Fig 25.29) • In the stomach, the low pH destroys tertiary and quaternary structure allows pepsin to digest specific peptide bonds • In the small intestine, pancreatic enzymes and intestinal brush border peptidases work at pH 7-8 • Trypsin - breaks bonds next to arginine or lysine • Chymotrypsin- breaks bonds next to phenylalanine or tyrosine • Liberated amino acids, and some dipeptides are absorbed through by several different carrier proteins via by facilitaed diffusion or Na+ linked co-transporters Absorption of other molecules LaPointe Spring ‘12 Slide #23 • Water • Nearly all that is ingested is reabsorbed via osmosis • Ions • Absorbed via diffusion, cotransport, and active transport • Vitamins • Water soluble vitamins (C and B vitamins) are absorbed by diffusion • Vitamin B12 requires intrinsic factor • Fat soluble vitamins (A,D, E, K) are absorbed as part of micelles Water Intake, Secretion and Absorption LaPointe Spring ‘12 Slide #24 Diarrhea Constipation from Seeley, Stephens and Tate Great Summary slide (a) LaPointe Spring ‘12 Slide #25 Marieb Figure 23.33a Great Summary slide (b) LaPointe Spring ‘12 Slide #26 Marieb Figure 23.33b