DIGESTIVE SYSTEM

• Mucosal wall architecture


  • Mouth
  • Tongue
  • Salivary Glands
  • Pharynx
  • Stomach
  • Small Intestine
  • Large Intestine
  • Pancreas
  • Liver

  
• Tongue


  • Muscular organ that occupies the floor of the oral cavity
  • Facilitate speech, mastication (chewing), and assists in swallowing
  • Responsible for sense of taste

  
• Salivary Glands


  • Lubricate the mouth
  • Allows you swallow
  • Aids in digestion
  • Protection
• Major Types of Salivary Glands

  • Sublingual
  • Submandibular
  • Parotid

  
• Pharynx


  • Bolus passes through from the mouth
  • Deglutition-swallowing
  • Epiglottis- reflexively covers the glottis (opening of the trachea; creates a ramp to direct the bolus into the esophagus)
• Stomach


  • Mechanical and chemical digestion are increased
  • Gastric rugae, these folds accommodate the expansion of the organ
  • Cardia- attachment of the esophagus to the stomach
  • The tissue from epithelium that resist friction becomes epithelium that resists the harsh chemical environment

  
• Categories of Cells in the Stomach

  • SLC- surface lining cells, line the luminal surface of the stomach; tight junction complexes from adjacent cells creating a watertight barrier
  • Parietal cells- HCL- producing cells
  • Zymogenic cells (gastric chief cells)- secrete an enzyme-rich mixture; pepsinogen
  • Enteroendocrine cells- hormones response to stomach activity

  
• Divisions of the Stomach

  • Cardia- gastric glands rich in mucus producing cells protect against the harmful acid
  • Fundus- densely populated with parietal cells
  • Pylorus- mucus-produce cells that neutralize the stomach acid
  • Pyloric sphincter – regulates the passage of material

  
• Small Intestine


  • 20 ft long
  • Digested materials are absorbed into the blood and lymphatic system
  • Plicae circularis- are circular folds found in duodenum and jejunum; they are covered with villi-microvilli where absorptive cells are located
  • Intestinal villi- vascular and have lymphatic vessels
  • Ileum, final segment which produces a variety of enzymes and agents such as lysozyme and several immune system cytokines that are essential for immune system

  
• Cell Types in the Small Intestine

  • Surface absorptive cells- numerous microvilli to absorb material from intestinal lumen
  • Goblet cells- mucus secreting cells become more abundant in the mucosal lining
  • Enteroendocrine cells- produce hormones; produce gastric inhibitory peptide; produce cholecystokinin

  
• Large Intestine


  • 5ft in length, 3 inches in diameter
  • Mostly absorb water (approx. 1400 ml per day)
  • Compacts the material into solid waste (feces; 100 ml/day)
  • Muscular sphincter (Ileocolic valve), allows food from small intestine to large intestine
  • Spasmodic contraction- helps move the fecal material father along the colon
  • Rectum- the final segment of the colon is the rectum which functions for the storage of feces and its elimination(defecation)
  • Two muscular sphincters: internal anal sphincter is under involuntary and is always in a state of contraction and external sphincter is voluntary and is made up of skeletal muscle

  
• Pancreas


  • Accessory digestive gland
  • Exocrine secretion pass through the pancreatic duct into common bile duct and enter to duodenum
  • Pancreatic cells secretes a solution of digestive enzymes (pancreatic juice) to further degrade carbohydrates, proteins, and fats

  
• Liver


  • Blood from digestive tract is brought to the liver via hepatic portal vein; this nutrient-rich blood is spread throughout the open spaces of the liver and forced to make contact with hepatocytes to metabolize the material
  • Blood-filtering
  • Bile-producing (breakdown fats into fatty acid)
  • Storage facility of carbohydrate and vitamins (A, D, B)
  • Fats are metabolized and regulated