Digestive System

• Gastrointestinal tract

  Mouth, pharynx, esophagus, stomach, small intestine, large intestine
• Accessory organs

  Teeth, tongue, salivary glands, liver, gallbladder, pancreas

  
• Tunics (of digestive system)

  • Mucosa: mucous membrane attached to thin layer of visceral muscle
  • Submucosa: loose connective tissue
  • Muscularis: skeletal or smooth muscle
  • Adventitia: serous membrane made of connective and epithelial tissue
• Mastication


  The process of chewing and mixing food with saliva
• Mouth or oral cavity

  • Cavity lined with mucous membrane
  • Cavity floor formed by tongue
  • Cavity roof formed by hard and soft palate
  • Cavity sides formed by cheeks
  • Cavity opening guarded by lips
• Tongue


  • Food manipulation, taste, speech
  • Skeletal muscle covered with mucous membrane
  • Papillae with taste buds
• Saliva


  • 99.5% water
  • Contains amylase to digest carbohydrates
  • Buffered by bicarbonates and phosphates
  • Contains mucin to lubricate food
  • Contains lysozyme to destroy bacteria
• Teeth


  • Crown, neck, root
  • Crown covered in enamel
  • Dentin: bonelike substance enclosing pulp cavity
  • Cementum: covers root
  • Periodontal ligament: anchors tooth
• Pharynx


  • Common passageway for food and air
  • Divisions: nasopharynx, oropharynx, laryngopharynx
  • Function: begins swallowing (deglutition), forms food bolus, air passageways close
• Esophagus


  • Secretes mucus
  • Transports food via peristalsis
  • Lower esophageal sphincter controls passage of food into stomach

  
• Stomach


  • Parts: cardia, fundus, body, pylorus
  • Rugae: epithelial folds
• Functions of the stomach

  • Store food
  • Produce mucus to protect stomach
  • Mechanical digestion via churning action
  • Mix food with hydrochloric acid to denature protein and eradicate pathogens
  • Produce chyme
  • Produce intrinsic factor
• Regulation of gastric juice secretion

  1. Cephalic phase: sight, taste or smell of food stimulates secretion

  2. Gastric phase: food entry stimulates gastrin secretion, acid secretion inhibits gastrin

  3. Intestinal phase: acid entry into duodenum stimulates secretin and cholecystokinin to reduce gastric secretion and motility
• Pancreas


  • Produces enzymes for digestion
  • Produces hormones insulin and glucagon
• Liver


  • Produces bile to aid digestion
  • Metabolises nutrients
• Gallbladder


  • Pear-shaped sac
  • Stores and concentrates bile and it is located in depression on surface of liver
• Small intestine


  • Divisions: duodenum, jejunum, ileum
  • Plicae: folds to increase surface area
  • Villi: site of nutrient absorption, contain microvilli, arteriole, venule, capillary, lacteal
  • Crypts of Lieberkuhn: secrete digestive enzymes
  • Brunner's glands: secrete alkaline mucus
  • Chyme: digested contents

  
• Functions of small intestine

  Absorption of digested food

  
• Large intestine


  • Reabsorption of water
  • Manufacture and absorption of vitamins
  • Formation and expulsion of feces
  • Cecum, colon, rectum, anus
• Feces


  • Semisolid mass originating from chyme
  • Contains water, inorganic salts, epithelial cells, Escherichia coli
• Tongue


  • Food manipulation, taste, speech
• Structure of tongue


  Skeletal muscle covered with mucous membrane, Papillae
• Teeth


  Crown, neck, root
• Crown


  • Covered in enamel
• Dentin


  Bonelike substance enclosing pulp cavity
• Cementum


  Covers root
• Periodontal ligament


  Anchors tooth
• Pharynx


  Common passageway for food and air, Divisions: Nasopharynx, oropharynx, laryngopharynx, Function: Begins swallowing (deglutition), Forms food bolus, Air passageways close
• Esophagus


  Secrete mucus, Transport food, Peristalsis: smooth muscle contractions push food, Lower esophageal sphincter: Controls passage of food into stomach
• Regulation of gastric juice secretion

  1. Cephalic phase: Sight, taste or smell of food stimulates secretion

  2. Gastric phase: Food enters stomach, hormone gastrin secreted, secretion of hydrochloric acid reduces pH

  3. Intestinal phase: Acidic contents enter duodenum, hormones secretin and cholecystokinin (CCK) secreted, reduce gastric juice secretion and motility
• Pancreas


  Islet cells produce insulin and glucagon, Acini glands produce pancreatic juice, Pancreatic juice travels to duodenum, Bicarbonate ions give high pH to protect small intestine, Pancreatic juice contains amylase, lipase, trypsinogen, chymotrypsinogen, procarboxypeptidase
• Small intestine


  • Plicae: folds, Villi: site of nutrient absorption, Microvilli increase absorption area, Villus contains arteriole, venule, capillary network, and lacteal, Crypts of Lieberkuhn secrete digestive enzymes, Brunner's glands secrete alkaline mucus
• Digestive hormones


  • Gastrin
  • Secretin
  • Cholecystokinin (CCK)
  • Insulin
  • Glucagon
• Ingestion: taking food into the digestive system
• Propulsion: moving the food along the length of digestive system
• Digestion: breaking down food. this can be achieved mechanically as food is chewed or moved through the digestive system, or chemically by the action of enzymes mixed with the food as it moves through the digestive system.
• Absorption: the products of digestion exit the digestive system and enter pthe blood or lymph capillaries for distribution to where they are required
• Elimination: the waste products of digestion are excreted from the body as faeces
• Gastrointestinal tract: mouth, pharynx, esophagus, stomach, small intestine, large intestine
• Tunic: ( from inside out)