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Chapter 14 Digestive System Anatomy and Physiology II Ms. Harborth PART I: Digestive System Takes in food (ingests) Breaks it down physically (digests) Absorbs nutrients Rids body of indigestible remains (defecates) Anatomy of the Digestive System Alimentary canal (GI tract) ◦ Ingests, digests, absorbs, defecates Accessory digestive organs ◦ Teeth, tongue, large digestive glands Alimentary Canal Continuous, hollow muscular tube Submucosal and myenteric nerve plexuses 30 feet long in cadaver ◦ ◦ ◦ ◦ ◦ ◦ ◦ Mouth Pharynx Esophagus Stomach Small intestine Large intestine Anus Mouth Labia Cheeks Hard and soft palate Uvula Vestibule Oral cavity proper Tongue Lingual frenulum Pharynx Oropharynx Laryngopharynx 2 skeletal muscle layers ◦ Inner layer longitudinal ◦ Outer layer circular Peristalsis Esophagus 10 inches long 4 tissue layers ◦ ◦ ◦ ◦ Mucosa – innermost Submucosa Muscularis externa Serosa Visceral peritoneum Parietal peritoneum Mesentery Stomach 10 inches long, can hold 1 gallon Diameter changes Cardiac region ◦ Cardioesphageal sphincter Fundus Body Pylorus ◦ Pyloric sphincter Stomach Rugae Greater curvature Lesser curvature Lesser omentum Greater omentum Stomach Gastric pits ◦ Gastric glands ◦ Gastric juice Ex: Intrinsic factor Chief cells ◦ pepsinogens Parietal cells Mucous neck cells Chyme Small Intestine 6-13 ft long Ileocecal valve Duodenum Jejunum Ileum Pancreatic ducts Bile duct Peyer’s patches Food Absorption Microvilli Villi ◦ Lacteal lymphatic capillary Circular folds Large Intestine 5 ft Cecum Appendix Colon ◦ ◦ ◦ ◦ Ascending colon Transverse colon Descending colon Sigmoid colon Rectum Anal canal Accessory Digestive Organs Salivary glands ◦ Parotid glands ◦ Submandibular glands ◦ Sublingual glands Saliva ◦ Bolus ◦ Salivary amylase ◦ Lysozyme and IgA antibodies Accessory Digestive Organs Teeth ◦ ◦ ◦ ◦ ◦ ◦ ◦ Masticate Deciduous teeth Permanent teeth Incisors Canines Premolars (bicuspids) Molars Teeth Continued Crown and Root Gingiva Enamel Neck Cementum Periodontal membrane (ligament) Dentin Pulp cavity Pulp Root canal Accessory Digestive Organs Pancreas ◦ Retroperitoneal ◦ Digestive enzymes in alkaline fluid ◦ Endocrine organ Accessory Digestive Organs Liver and Gallbladder ◦ Liver 4 lobes Bile Common hepatic duct ◦ Gallbladder Cystic duct Stores and concentrates bile Functions of Digestive System 1. Ingestion 2. Propulsion 3. Food breakdown: mechanical digestion 4. Food breakdown: chemical digestion 5. Absorption 6. Defecation digestion animation Digestion Reflexes Mechano/Chemoreceptors triggered by: ◦ Stretch of organ by food ◦ pH of contents ◦ Presence of certain breakdown products Activate or Inhibit: ◦ Glands that secrete digestive juices or hormones ◦ Smooth muscles that mix and propel food Activities of Mouth, Pharynx, and Esophagus Mouth – mechanical and chemical digestion Deglutition (tongue, soft palate, pharynx, and esophagus) ◦ Buccal phase ◦ Pharyngeal-esophageal phase FYI: Swallowing can occur while standing on your head! Activities of Stomach Sight, smell, and taste of food stimulates parasympathetic reflexes ◦ Gastric juices secreted ◦ Hormone gastrin released Makes stomach glands produce pepsinogens, mucus, and HCl FYI:You make 2-3 Liters of gastric juice a day! Chemistry in the Stomach HCl makes pepsinogen pepsin Rennin: works on milk protein (only in infants) Hardly any chemical digestion occurs ◦ Aspirin and alcohol are absorbed through stomach wall Food Propulsion from Stomach Chyme is end product Pylorus only allows liquid and small particles to pass through sphincter Each contraction squirts 3 ml of chyme Rest is squeezed back into stomach ◦ Causing enterogastric reflex FYI: It usually takes 4 hours for your stomach to empty, or 6 hours if meal was high in fat Activities of Small Intestine Carb and protein digestion had begun in stomach, but no fat digestion Microvilli make few enzymes ◦ Brush border enzymes ◦ Hormones: Secretin Cholecystokinin (CCK) Pancreatic juices are enzyme and bicarbonate rich ◦ ◦ ◦ ◦ Complete digestion of starch Carry out ½ of protein digestion Responsible for fat digestoin Digest nucleic acids Absorption in Small Intestine Water and end products absorbed through intestinal cell plasma membranes via active transport ◦ Except lipids – absorbed through diffusion Then to the hepatic portal vein By the end of ileum, only water and indigestible food materials and LOTS of bacteria FYI: Takes about 3-6 hours for food to go through small intestine Activities of Large Intestine Bacteria metabolize and release gases (methane and hydrogen sulfide) and some vitamins These gases make feces smell Peristalsis and mass movements Defecation reflex PART II: Nutrition and Metabolism Major nutrients ◦ Carbohydrates ◦ Lipids ◦ Proteins Vitamins and minerals Water Metabolism Catabolism and anabolism Carbohydrate metabolism Fat metabolism Protein metabolism Carbohydrate Metabolism Glucose ATP Cellular respiration ◦ Glycolysis, Krebs cycle, electron transport chain Fat Metabolism Liver Fat is broken down to acetic acid Acetic acid is broken down in mitochondria to make ATP, CO2, and water Protein Metabolism Proteins are broken down into amino acids Cellular uptake 20 amino acids are needed, 8 can’t be made by our cells (“essential amino acids”) IF no other energy source is available, amine groups are removed as ammonia, and rest is used by mitochondria for ATP Liver’s Role in Metabolism Used in digestion, detoxifying drugs & alcohol, degrades hormones, makes cholesterol, albumin, clotting proteins and lipoproteins, and METABOLISM Blood circulates through, liver grabs nutrients and macrophages kill pathogens Liver Glycogenesis Glycogenolysis Gluconeogenesis Cholesterol HDL and LDL Body Energy Balance Energy intake = heat + work + energy source Rising or falling blood levels of nutrients, hormones, or body temperature affect eating behavior Psychological factors influence as well Metabolic Rate Basal metabolic rate ◦ Amount of heat produced when at rest ◦ Influenced by: Surface area Sex Age Emotions Amount of thyroxine Total metabolic rate ◦ Amount of kilocalories body needs to fuel all activities ◦ Stays elevated well after exercise Body Temperature Regulation Hypothalamus ◦ Heat-promoting mechanisms Vasoconstriction Shivering ◦ Heat loss mechanisms Radiation through skin
