Digestive system

• Three main groups of nutrients needed are:

  • Carbohydrates (starch and glucose)
  • Proteins
  • Fats
• Digestion breaks down food into tiny pieces for absorption into body cells
• Digestion involves both physical breakdown (chewing) and chemical breakdown by enzymes
• In the mouth:

  • Food is physically broken down by chewing
  • Saliva from salivary glands contains salivary amylase enzyme to break down carbohydrates
• In the stomach:

  • Muscular sac that contracts to mix food
  • Produces pepsin enzyme to break down proteins
  • Produces hydrochloric acid to create the right environment for pepsin to work
• After stomach, food moves to the small intestine for absorption into the bloodstream:

  • Most digestion takes place in the small intestine
  • Pancreas produces most digestive enzymes and releases them into the small intestine
  • Gallbladder releases bile to neutralize stomach acid and emulsify fats
• Bile is made in the liver and stored in the gallbladder
• Small intestine has adaptations for absorption:

  • Villi increase surface area for absorption
  • Single layer of surface cells for quick diffusion
  • Good blood supply to maintain concentration gradient
• Large intestine absorbs excess water from leftover material in the small intestine, leaving behind feces in the rectum
• Order of the digestive process:

  • Food in mouth
  • Chewing and saliva in mouth
  • Swallowing into the stomach
  • Mixing with pancreatic juices and bile in the small intestine
  • Digestion and absorption into the bloodstream in the small intestine
  • Absorbing excess water in the large intestine
  • Feces stored in the rectum