Gastrointestinal system

• Digestion


  Breakdown of ingested food
• Absorption


  Passage of nutrients into the blood
• Metabolism


  Production of cellular energy (ATP)
• Alimentary canal


  • mouth
  • pharynx
  • esophagus
  • stomach
  • small intestine
  • large intestine
• Accessory digestive organs


  • teeth
  • tongue
  • gallbladder
  • salivary glands
  • liver
  • pancreas
• Gastrointestinal tract


  A continuous, hollow coiled tube that digests food, breaks it down, and absorbs the fragments through its lining into the blood
• Ingestion


  1. Taking food into the digestive tract

  2. Act of putting food into mouth
• Mechanical digestion


  1. Chewing, mixing, and churning food

  2. Biting: using of teeth to cut the food

  3. Mastication: chewing or grinding of food
• Chemical digestion


  1. Catabolic breakdown of food

  2. Initial digestion: stomach

  3. Final digestion: small intestine
• Absorption


  Movement of nutrients from the GI tract to the blood or lymph (villi and microvilli)
• Propulsion


  1. Deglutition and peristalsis

  2. Deglutition: swallowing

  3. Peristalsis: waves of contraction and relaxation of muscles in the organ walls
• Defecation


  Elimination of indigestible and unabsorbed solid wastes (large intestine)
• Lips


  • Protect the anterior opening
• Cheeks


  • Form the lateral walls
• Hard palate


  • Forms the anterior roof
• Soft palate


  • Forms the posterior roof
• Uvula


  • Fleshy projection of the soft palate
• Vestibule


  • Space between lips externally and teeth and gums internally
• Tongue


  • Attached at hyoid & styloid processes, and by the lingual frenulum
• Frenulum


  • Membrane that secures the tongue to the floor of the mouth; limits movement
• Mastication


  Chewing of food (mechanical digestion)
• Chemical digestion


  Mixing masticated food with saliva
• Salivary amylase


  Enzyme that digests starch
• Mucin


  Slippery protein (mucus), protects soft lining of digestive system; lubricates food for easier swallowing
• Buffers


  Neutralize acid to prevent tooth decay
• Anti-bacterial chemicals


  Kill bacteria that enter mouth with food
• Pharynx


  Serves as a passageway for air and food
• Food movement in pharynx


  1. Propelled to the esophagus by two muscle layers

  2. By alternating contractions of the muscle layers called peristalsis
• Esophagus


  Runs from pharynx to stomach through the diaphragm
• Stomach


  • Located on the left side of the abdominal cavity (~10 in long)
  • When full holds about 1 gallon of food
  • Food enters the stomach at the cardioesophageal sphincter
  • Food exits the stomach at the pyloric sphincter between stomach & small intestine
• Pepsin


  An enzyme that breaks down proteins; secreted as pepsinogen; activated by HCl
• Motilin


  A polypeptide that has a role in fat metabolism
• Gastrin


  A hormone that stimulates the production of gastric acid in the stomach
• Secretin


  A peptide hormone secreted by the duodenum that serves to regulate its acidity
• Heartburn


  Occurs when the cardio-esophageal sphincter fails to close tightly and gastric juice backs up into the esophagus
• Hiatal hernia


  Superior part of the stomach protrudes above the diaphragm allowing juices to go into the esophagus
• Vomiting


  Reverse movement of food, brought about by a signal from the medulla
• It takes 4 hours for the stomach to empty after a well-balanced meal and 6 hours for a fatty meal
• Small Intestine


  • 4 to 8 hours
  • The body's major digestive organ
  • Site of nutrient absorption into the blood
  • Muscular tube extending from the pyloric sphincter to the ileocecal valve
  • Suspended from the posterior abdominal wall by the mesentery
• Duodenum


  • Attached to the stomach
  • Curves around the pancreas (10 in)
  • Most digestion