The Digestive System (Organs and Functions)

• Phases of digestion

  1. Ingestion
  2. Movement
  3. Mechanical and Chemical Digestion
  4. Absorption
  5. Elimination
• Mechanical (physical)

  • chew
  • tear
  • grind
  • mash
  • mix
• Chemical - Enzymatic reactions to improve digestion of carbohydrates, proteins, and lipids
• Digestive System Organization

  Gastrointestinal (GI) tract

  • mouth
  • pharynx
  • esophagus
  • stomach
  • small intestine
  • large intestine
  • rectum
• Swallowing is involuntary movement of food from mouth through esophagus to stomach.
• Epiglottis: flap-like structure at the back of the throat.
• Teeth mechanically break down food into small pieces.
• Tongue mixes food with saliva (contains amylase, which helps break down starch).
• Esophagus

  • approximately 20 cm long
  • Functions include: Secreting mucus and moving food from the throat to the stomach using muscle movement called peristalsis

  
• Food found in the stomach is called chyme. It is a mixture of food and digestive juices.
• Stomach - J-shaped muscular bag that stores the food and breaks it down into tiny pieces
• Hydrochloric acid in the stomach kills bacteria
• Stomach mixes food with gastric juices that contains enzymes to break down proteins and lipids
• Small intestines are roughly 7 meters long
• Lining of intestine walls has finger-like projectionscalled villi, to increase surface area
• villi are covered in microvilli which further increases surface area for absorption

  
• Nutrients from the food pass into the bloodstream through the walls of the small intestine
• Small Intestine absorbs:

  • 80% ingested water
  • Vitamins
  • Minerals
  • Carbohydrates
  • Proteins
  • Lipids
• Large Intestine is about 1.5m long
• Large intestine absorbs nutrients left behind by the small intestines.
• The end of the large intestine is the rectum. (short term storage which holds feces before it is expelled)
• Large intestine functions

  • Bacterial digestion and fermentation of carbohydrates
  • Absorbs additional water
  • Concentrates wastes
• Accessory Organs - The Glands

  • Not part of the path of ingested food, but play a critical role in digestion.
• The glandural organs includes:

  • Liver
  • gall bladder
  • pancreas
• Liver directly affects digestion by producing bile
• Bile aids in the digestion of fat
• Liver filters out toxins and waste including drugs, alcohol and poisons
• Gall Bladder stores bile from the liver, releases it into the small intestine.
• Fatty diets can cause the formation of gallstones, which can cause pain and blockage
• Pancreas produces digestive enzymes to digest fats, carbohydrates and proteins
• Pancreas regulates blood sugar by

  producing insulin