Chapter 15 Gastrointestinal Tract Fluid Professor A. S. Alhomida

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1 Disclaimer The texts, tables, figures and images contained in this course presentation (BCH 376) are not my own, they can be found on: References supplied Atlases or The web King Saud University College of Science Department of Biochemistry Chapter 15 Gastrointestinal Tract Fluid Professor A. S. Alhomida 1 Secretions of the Gastrointestinal (GI) Tract 1. Primary Organs Salivary Gastric Pancreatic Intestinal 2. Accessory Organs Teeth Tongue Gallbladder Liver Length of GI tract vs height 2 1

2 GI Tract Anatomy 3 Stomach cardia fundus pylorus body 4 2

3 Daily Secretion of Digestive Fluids Fluid Volume (ml/day) ph Saliva Stomach (gastric secretion) Pancreas (exocrine secretion) Bile secretion Brunner s s gland secretion Succus entericus (intestinal juice) Large intestine Enzymes of GI Tract 6 3

4 Hormones of GI Tract 7 Digestive Process 1. Ingestion- taking food in Bolus- an amount of food passing through tract 2. Propulsion- moves food through tract Swallowing- voluntary Peristalsis- involuntary muscular waves moves food forward 3. Mechanical digestion- physical chewing, mixing, churning Segmentation- rhythmic local constrictions of intestine for mixing 8 4

5 Digestive Process, cont d 4. Chemical digestion- catabolism/ breakdown of polymers into monomers by enzymes Begins in mouth, essentially complete in small intestine 5. Absorption- passage of digested end products across wall into blood Monomers, vitamins, minerals and water Pass through mucosal cells lining tract Small intestine major absorption site 6. Defecation- eliminates indigestible substances and other wastes from body via anus in form of feces 9 Digestive Process 10 5

6 Functions of Saliva 1. Maintenance of oral hygiene Lysozyme, peroxidases (XEROSTOMIA) 2. Maintain mineralization of teeth (Ca 2+ and ph) 3. Lubrication Speaking and swallowing (mucin) 4. Digestive function Amylase (Ptyalin) & Lipase 5. Solvation Enables one to taste foodstuffs 11 Three Major salivary glands % Total Type 1. Submandibular (submaxillary): 70% sero-mucin 2. Parotid: 25% serous (protein) 3. Sublingual: 5% mucin (mucus) Total 1,500 ml/day 12 6

7 Salivary Gland Structure 13 Salivary Gland Structure Acinus intercalated ducts striated ducts excretory duct 14 7

8 Salivary Flow Rate Na 140 Ion concentration (mm mm) Flow rate (ml Saliva ml/min) Na HCO 3 Cl K Cl HCO 3 K Plasma Ion concentration (mm mm) Composition of Human Saliva 16 8

9 Salivary Gland Diseases 1. Functional disorders Sialorrhea (Increase in saliva flow) Psychosis, mental retardation, certain nuerologicval diseases, rabies, Mercury poisoning Xerostomia (Decrease in saliva flow) Mumps, sardoidosis, Sjogrens, syndrome, lupus, postirradiation 17 Salivary Gland Diseases 2. Obstructive disorders 3. Non-neoplastic disorders 4. Neoplastic disorders 18 9

10 Salivary Calculi 1. It sometimes is formed in the ducts and similar composition to tartar (Ca(PO 4 ) 2 or CaCO 3 2. It is usually stated that a nucleus around which the precipitation body of these salts occur 3. Calcium oxalate may be the precipitated salt which together with mucin and globulin may form the calculi 4. Increased acidity is necessary for oxalate calculus formation 19 Pancreatic Structure 1. Endocrine cells They are arranged in small islets within the pancreas, secrete directly into the circulation: Insulin Glucagon Somatostain Polypeptids 20 10

11 Pancreatic Structure, Cont d 2. Exocrine cells They are organized into acini that produce four types of digestive enzymes: Peptidases Lipases Amylases Nucleases 21 Pancreatic Structure, Cont d 3. Ductal cells Each day they secrete about ml of pancreatic juice containing a high concentration of - HCO 3 The HCO - 3 neutralizes gastric acid and regulates the ph of the upper intestine Failure to naturalize the chyme as it enters the intestine will result duodenal ulcers 22 11

12 Pancreatic Juice Composition 23 Pancreas Structure 24 12

13 Pancreatic Secretion 25 Pancreatic Secretion ph ph Osm Osmolality Ion Concentration (mm mm) Na + HCO 3 Cl - K Secretion rate (ml( ml/hr)

14 Functions of Gastric Secretions 1. Digestion of proteins (pepsinogen and HCl) 2. Protection of stomach (HCO - 3 and mucus) 3. Absorption of vitamin B 12 (intrinsic factor) 4. Destroy bacteria and other microorganisms (HCl) 27 Gastric Juice Composition 28 14

15 Gastric Secretions 29 Gastric Pit mucus neck & surface cells Mucus & HCO 3 Peptic cells (chief, zymogen) Pepsinogen secretion parietal cells (oxyntic) H + secretion & intrinsic factor 30 15

16 HCl Section Mechanism 1. HCl is secreted into the parietal cell canaliculi by a three step process: Active transport process is begun by transport of K + and Cl - into the canaliculi. C l- is transported by either a pump or through a channel. The flow of Cl- creates a ve potential inside the canaliculi,, causing K+ to flow +vely+ into the canaliculi H + is exchanged for K + by H + -K + ATPase pump Water enters the canaliculi down the osmotic gradient created by the movement of HCl into the canaliculi 31 HCl Section Mechanism, Cont d 2. The H + entering the canaliculi is supported by dissociation of carbonic acid (H 2 CO 3 ) into H + and bicarbonate (HCO - 3 ) within the parietal cell: H 2 CO 3 is formed from the Rxn catalyzed by carbonic anyhydrase: CO 2 + H 2 O H 2 CO 3 HCO - 3 diffuses back into the plasma in exchange for Cl - 3. Most the HCl that is secreted into the stomach is neutralized and reabsorbed within the small intestine 32 16

17 HCl Section Mechanism, Cont d 4. Active transport process involved in the generation of HCl requires a large amount of ATP which is generated by mitochondria in parietal cell 5. The ph of the parietal cell secretion can be as low as The H + -K + ATPase pump can irreversible inhibited by the drug omeprazole (antacid) which is used now for the treatment of duodenal and gastric ulcers 33 HCl Section Mechanism, Cont d 34 17

18 Regulation of Gastric Secretion 1. Cephalic Food in mouth increases secretion of HCl (efferent vagus) Anger and tension increases secretion HCl Fear and depression increases secretion HCl 2. Gastric Stimulated by distension (vago-vagal), hypertonicity Alcohol and AAs (gastrin) Inhib by H + (-ve feedback, somatostatin) 3. Intestinal Peptides (gastrin), AA s, fats CCK-PZ) 35 Regulation of Gastric Secretion 36 18

19 Gastric Ulcers 1. Ulcer (sore) in inner lining of stomach Chronic bleeding into GI tract Anemia may result Perforated ulcer Stomach contents spill into abdomen 2. Caused by Helicobacter pylori (bacterium) Antibiotics cure problem 37 Gastric Ulcers, Cont d An ulcer is a crater-like lesion on the skin or mucous membrane caused by an inflammatory, infectious, or malignant condition To avoid irritating an ulcer a person can try eliminating certain substances from their diet such as caffeine, alcohol, aspirin, and avoid smoking Patients can take certain medicines to suppress the acid in the stomach 38 19

20 Small Intestine 1. Major digestive organ 2. Longest part of alimentary canal (3-6 hour journey) 3. Three subdivisions Duodenum Shortest but lots going on Hepatopancreatic ampulla- bile duct and main pancreatic duct enter Jejunum Middle portion Ileum Last part joins large intestine at ileocecal valve 39 Small Intestine 40 20

21 Intestinal Juice 1. Glands make 1-3 L daily 2. Stimulated by entrance of acidic chime 3. Slightly alkaline to neutralize chyme 4. Largely water with some mucus 5. Relatively enzyme poor because enzymes are bound to the brush border 41 Intestinal Juice Composition 42 21

22 Carbohydrate and Protein Digestion 43 Fat and Nucleic Acid Digestion 44 22

23 Large Intestine 1. Shorter but larger diameter than small intestine 2. Major function in feces elimination and water reabsoprtion hours 45 Large Intestine 46 23

24 Bacterial Flora 1. Most bacteria killed by stomach acid or enzymes 2. Some survive or come up from the anus 3. Ferment indigestible carbohydrates (cellulose and others) 4. Release acids and gases (about 500 ml/day) 5. Also release B complex vitamins and most of the body s vitamin K need (for clotting) 47 Bile Function of Bile Bile is required for the digestion and absorption of fats and for excretion of water-insoluble substances as cholesterol and bilirubin Formation of Bile It is formed from two sites: Hepatocytes Ductal cells 48 24

25 Bile, Cont d Storage of Bile Although it is secreted continuously, but it is stored in the gallbladder during the interdigestive period Release of Bile It is released into the duodenum during the digestive period 49 Bile Fluid 1. Flows toward bile duct branches in portal triads 2. Constantly made by hepatocytes 3. List of contents but bile salts and phospholipids important in digestion 4. Bile cholesterol is important because it is one of the few ways in which cholesterol stores can be regulated 50 25

26 Bile Salts Role of Bile Salts in Emulsifying Fat 1. Break up large glob into smaller globs 2. Makes for large surface area for lipid digesting enzymes 3. Facilitate fat and cholesterol absorption Most of bile (but not bile salts) will leave with feces Bile salts are actually recycled for reuse 51 Human Bile Composition 52 26

27 Bile Salts Role in Digestions 53 Bile Acids (Salts) Biosynthesis 1. Primary Acids 2. Secondary acids 54 27

28 Bile Acids (Salts) Biosynthesis, Con td 55 Recycling of Bile Salts 1. The total circulating pool of bile salts is about 3.6 g 2. Because g of bile salts are required to digest and absorb a meal (more if the meal is high in fat), the total pool of bile salts must circulate twice during the digestion of each meal 3. The bile salts usually circulate times daily 56 28

29 Recycling of Bile Salts, Cont d 57 Gallbladder 1. Pear-shaped muscular sack Attached to surface of liver 2. Stores excess bile Liver produces 1000 ml/day Water is reabsorbed Consistency of thick mucus 58 29

30 Gallbladder, Cont d 3. Bile duct empties into duodenum 4. Stores bile not immediately needed for digestion 5. Concentrates stored bile 6. Releases bile when foods high in lipids enter the small intestine 59 Gallbladder, Cont d 60 30

31 Gallstones 1. Gallstone = crystallized bile 80% of stones are cholesterol 20% bilirubin 2. Treatment Surgical removal (cholecystectomy) 500,000 surgeries/year Oral dissolution Sound waves break stones into small, passable pieces 61 Gallstones 1. Obstruction of the cystic duct leading to severe abdominal pain (biliary colic) 2. Infection or inflammation of the gallbladder (cholecystitis) 3. Blockage of the biliary ducts leading to the duodenum (biliary obstruction) 62 31

32 THE END Any questions? 63 32