Digestive

• Oral cavity


  Point of entry of food into the digestive system
• Mastication


  Chewing action of the teeth to break down food into smaller particles
• Saliva


  Watery substance produced in the mouths of many animals that moistens food and contains enzymes to begin digestion
• Salivary glands


  • Three major glands that secrete saliva: parotid, submandibular, and sublingual
• Salivary amylase


  Enzyme in saliva that begins converting starches into maltose
• Lingual lipase


  Enzyme produced by cells in the tongue that begins breaking down fats
• Bolus


  Mass of chewed and moistened food ready for swallowing
• Swallowing


  Tongue moves the bolus from the mouth into the pharynx
• Pharynx


  Opens to the trachea and esophagus
• Epiglottis


  Cartilaginous flap that covers the glottis (opening to the trachea) during swallowing to prevent food from entering the lungs
• Esophagus


  Tubular organ that connects the mouth to the stomach
• Peristalsis


  Wave-like muscle contractions that push food through the esophagus towards the stomach
• Gastro-esophageal sphincter


  Ring-like muscle at the stomach end of the esophagus that opens to allow food to enter the stomach and closes to prevent stomach contents from entering the esophagus
• Stomach


  Saclike organ that secretes gastric digestive juices and has a highly acidic pH to break down food
• Sphincter


  A ring-like muscle that forms valves in the digestive system
• Gastro-esophageal sphincter


  Located at the stomach end of the esophagus, opens in response to swallowing and pressure from food bolus, closes to prevent stomach contents from traveling up the esophagus
• In humans, there is no true sphincter, but the esophagus remains closed when there is no swallowing action
• Acid reflux or "heartburn"


  Occurs when the acidic digestive juices escape into the esophagus
• Stomach


  • A saclike organ that secretes gastric digestive juices
  • pH between 1.5 and 2.5, highly acidic environment required for chemical breakdown of food and extraction of nutrients
  • Can expand up to 20 times its resting size when filled with food
• Chyme is a mixture of food and digestive juices that is produced in the stomach
• Pepsin


  An enzyme that breaks peptide bonds and cleaves proteins into smaller polypeptides, helps activate more pepsinogen
• Pepsinogen


  The inactive form of pepsin
• Hydrochloric acid


  The primary acidic component of stomach juices, helps convert pepsinogen to pepsin and kills microorganisms
• Protein digestion in the stomach

  1. Pepsin breaks down proteins

  2. Hydrochloric acid helps convert pepsinogen to pepsin and creates acidic environment
• Chyme


  The partially digested food and gastric juice mixture that passes from the stomach to the small intestine
• Pyloric sphincter


  Regulates the movement of chyme from the stomach into the small intestine
• The stomach lining is protected from digestion by pepsin due to pepsinogen being inactive and the thick mucus lining
• Ulcers are open wounds in the stomach caused by bacteria (Helicobacter pylori) when the mucus lining is ruptured and fails to reform
• Small intestine


  • Organ where digestion of protein, fats, and carbohydrates is completed
  • Has a highly folded surface with finger-like projections called villi and microscopic projections called microvilli to increase surface area for absorption
  • Absorbed nutrients are carried to the liver via the hepatic portal vein
• The small intestine is over 6m long and is divided into the duodenum, jejunum, and ileum
• Duodenum


  The "C-shaped", fixed part of the small intestine where chyme mixes with pancreatic juices and bile to neutralize acidity and further digest food
• Jejunum


  The second part of the small intestine where most chemical digestion and nutrient absorption occurs
• Ileum


  The last part of the small intestine where bile salts and vitamins are absorbed
• Large intestine


  • Reabsorbs water from undigested food and stores waste material
  • Shorter in length but larger in diameter compared to small intestine
  • Home to many bacteria that aid in digestive processes
• Rectum


  The terminal end of the large intestine that stores feces until defecation
• Anus


  The opening at the far-end of the digestive tract where waste material is eliminated, controlled by involuntary and voluntary sphincters
• Accessory organs of the digestive system

  • Salivary glands
  • Liver
  • Pancreas
  • Gallbladder
• Liver


  Produces bile for fat digestion, processes vitamins and fats, and synthesizes plasma proteins
• Pancreas


  Secretes digestive juices containing enzymes and bicarbonate to neutralize stomach acid
• Gallbladder


  Stores and concentrates bile produced by the liver, secretes bile into the duodenum when fatty acids enter