BIOL 133 GI STUDY GUIDE

• Digestive system

  Function: Break down food into nutrients to be absorbed by the body
• Digestive system


  Cooperates with circulatory system to transport absorbed nutrients to cells
• Alimentary canal


  Continuous tube from mouth to anus, involved in digestion and absorption of food
• Accessory digestive organs


  Assist in digestion but are not part of the alimentary canal

  
• Alimentary canal


  1. Begins at mouth (oral cavity)

  2. Ends at anus
• Food passage


  1. Ingestion

  2. Digestion

  3. Absorption

  4. Defecation
• Accessory digestive organs


  Produce enzymes, mucus, and other substances essential for breaking down food
• Accessory digestive organs


  • Liver
  • Pancreas
  • Gallbladder
  • Salivary glands

  
• Layers of alimentary canal from lumen outwards

  • Mucosa
  • Submucosa
  • Muscularis externa
  • Serosa (or adventitia)
• The mucosa consists of epithelium and directly contacts the digested food
• Short lifespan of epithelium in alimentary canal

  Facilitates rapid turnover and renewal, ensuring maintenance of healthy barrier against pathogens and efficient nutrient absorption
• MALT in lamina propria

  Helps defend against pathogens and foreign substances that enter the digestive tract
• Smooth muscle in muscularis mucosa

  Helps facilitate movements of the mucosa, aiding in digestion and absorption processes
• Submucosa


  Contains connective tissue, blood vessels, lymphatics, and nerves, providing support and transporting absorbed nutrients
• Muscularis externa of stomach

  Has an additional layer of muscle called the oblique layer, which aids in mechanical digestion
• Serosa


  Covers the external surface of most abdominal organs and forms the visceral peritoneum

  
• Serosa is not found in the esophagus
• Receptors and nerves in the mouth

  Necessary for sensory perception, taste, temperature, and texture of food, as well as for initiating the swallowing reflex
• Myenteric and submucosal plexuses

  Regulate gastrointestinal motility, secretion, and blood flow

  
• Sympathetic activation


  Inhibits digestion, causing decreased motility and secretion
• Parasympathetic activation


  Stimulates digestion, increasing motility and secretion
• Blood vessels serving the digestive system

  Provide oxygen and nutrients to the digestive organs and carry away waste products
• Lacteals


  Absorb digested fats (lipids) and fat-soluble vitamins (e.g., vitamins A, D, E, K) from the intestinal lumen
• Hepatic portal system and liver

  Serve in blood supply to the digestive system
• Fluid between visceral and parietal peritoneum

  Serves as lubrication, reducing friction between these two layers during movements of the digestive organs
• Retroperitoneal


  Situated or occurring behind the peritoneum (e.g. kidney)
• The mouth performs both mechanical and chemical digestion
• Accessory organs and their functions

  • Salivary glands: Produce saliva containing enzymes that initiate the breakdown of carbohydrates
  • Liver: Produces bile, which emulsifies fats to aid in their digestion and absorption
  • Pancreas: Produces digestive enzymes (e.g., amylase, lipase, proteases) and bicarbonate ions to neutralize acidic chyme from the stomach
• Large intestine


  Absorb water and electrolytes from undigested food material and to form and store feces
• Processes of digestion


  • Ingestion
  • Propulsion
  • Mechanical digestion
  • Chemical digestion
  • Absorption
  • Defecation
• Ingestion


  Occurs in the mouth, where food is taken into the digestive tract
• Peristalsis


  Coordinated contraction and relaxation of muscles to move food through the digestive tract
• Mastication (chewing) and segmentation are examples of mechanical digestion
• Enzymes assist with chemical digestion
• Absorption


  Majority occurs in the small intestine

  
• Defecation


  Occurs in the rectum and anal canal
• The digestive system is controlled by both neural and hormonal regulatory mechanisms

  
• Mechanoreceptors, chemoreceptors, and osmoreceptors

  Detect mechanical stretch, chemical composition, and osmolarity changes respectively
• Extrinsic and intrinsic nerve plexuses


  Stimulate long and short reflexes respectively
• Cephalic reflex


  Initiated when the sight or smell of food increase secretion of digestive juices (e.g. saliva)