Digestive System

• Digestive system


  Function is to break down food via hydrolysis into simpler substance nutrients
• Functions of digestive system

  • Elimination of undigested food residues
  • Absorption of digested nutrients
  • Homeostatic regulation of calcium, iron, phosphate
• Digestion


  1. Begins at mouth

  2. Five basic activities: Ingestion, Peristalsis, Digestion, Absorption, Defecation
• Ingestion


  Taking of food in the body
• Peristalsis


  Physical movement or pushing of food along the digestive tract
• Digestion


  Breakdown of food by both mechanical and chemical mechanisms to allow body's cell convert food energy into the high energy ATP molecules run cell's machinery
• Absorption


  Passage of digested food from the digestive tract into the cardiovascular & lymphatic systems for distribution to body's cells
• Defecation


  Elimination from the body of those substances that are indigestible & cannot be absorbed
• Organs of digestion


  • Gastrointestinal Tract / Alimentary Canal
  • Accessory organs
• Gastrointestinal Tract / Alimentary Canal


  Long tube, runs through the ventral cavity of body extends from mouth to anus, 30 ft. or 9 meters, Organs: Mouth, oropharynx, esophagus, stomach, small & large intestines
• Accessory organs


  Teeth, tongue, salivary glands, liver, gallbladder and pancreas
• Tunics of Alimentary canal

  • Tunica mucosa
  • Tunica submucosa
  • Tunica muscularis
  • Tunica Serosa(Adventitia)
• Tunica Mucosa


  Innermost, consists of mucous membrane attached to thin layer of visceral muscle, Three layers: Epithelial tissue layer, Lamina Propria, Muscularis Mucosa
• Tunica Submucosa


  Loose connective tissue, binds tunica mucosa to tunica muscularis
• Tunica Muscularis


  Contains major nerve supply to the alimentary canal -- Plexus of Auerbach
• Tunica Serosa / Adventitia


  Serous membrane, made up connective and epithelial tissue -- Visceral Peritoneum, Covers organ and its large folds, weave in and between organs, binding organs to each others and to walls of cavity, Contains blood and lymph vessels, nerves that supply organs
• Mouth or Oral Cavity


  Digestion begins here, Mechanical digestion of food with teeth and tongue, Functions: taste, chemical digestion of carbohydrate using the salivary enzyme : amylase
• Parts of mouth


  • Buccal cavity
  • Sides - cheeks
  • Roof - hard and soft palates
  • Floor - tongue
  • Lips - fleshy folds surround the opening or orifice of the mouth
• Hard palate


  Forms anterior part of the roof of the mouth, bony
• Soft palate


  Posterior portion of the roof of mouth, muscular
• Uvula


  Cone shaped, hanged from posterior border, Function in swallowing process & prevents food from backing up into nasal area
• Tongue


  Form floor of the oral cavity, Consist of skeletal muscle covered w/ mucous membrane, Divided into symmetrical halves by a septum --- lingual frenulum, Attached & supported by hyoid bone, Contains extrinsic & intrinsic skeletal muscles, Papillae covers the upper surface and side, Filiform Papillae important for licking
• Salivary Glands


  • Buccal Gland
  • Parotid Gland
  • Submandibular / Submaxillary Gland
  • Sublingual Gland
• Saliva


  Contains 99% water, contains amylase, volume of 1-1.5 liters within 24 hrs, Immunoglobulin A found in saliva, Functions: Moistened Food, Ingested food
• Pharynx


  Passage of air, food and water, Function in digestive system, process of swallowing or deglutition, Three parts: Nasopharynx, oropharynx, Laryngopharynx
• Esophagus


  10 inches, secrete mucus and transport food to the stomach, LES (Lower Esophageal Sphincter) separate esophagus from stomach prevent esophageal ulcer, Chyme - Food meet the acid in stomach
• Stomach


  Temporary storage of food, Secretes 1500 - 3000 mL of gastric juice per day, 3 mL within 24 hrs (acids), 1.1 - 2.4 gastric pH normal, Parts: fundus, pylorus or antrum, cardia
• Gastrin


  Stimulate gastric acid, Produced by G-cells which stimulates the production of HCl from parietal cells and pepsinogen by chief/zymogenic cells
• Intrinsic Factor


  Produced by parietal, needed for absorption of Vitamin B12
• Gastric glands


  Three kinds of secreting cells: Zymogenic or chief cells - secrete pepsinogen, Parietal Cell - secrete hydrochloric acid, Mucous cells - secrete mucus that protects the stomach
• Secretin


  Secretes enzymes amylase, Lipase, Pepsin
• CCK Cholecystokinin


  Emulsify fats, trigger Gallbladder to release bile & enzyme
• Phases of Digestion


  • Cephalic Phase
  • Gastric Phase
  • Intestinal Phase
• Cephalic Phase


  Sight/ smell or thought of food will stimulate the vagus to send signals to the stomach, stomach will produce gastric juices by gastrin
• Gastric Phase


  Presence of food on stomach increases acid, Bolus of food reaches the antrum
• Intestinal Phase


  Arrival of food in the duodenum
• Parts of Small Intestine

  • Duodenum
  • Jejunum
  • Ileum
• Ileocecal Valve


  Opening of small intestine
• Villi


  Hair like structure seen in the small intestine and help absorb digested food nutrients
• Peristalsis


  Involuntary wave like muscle contraction pushing bolus of food in small intestines