Human diet and digestion

• Necessary food groups in a balanced diet

  • Carbohydrates
  • Proteins
  • Lipids
  • Vitamins
  • Minerals
  • Dietary Fibre
  • Water
• A balanced diet consists of all of the food groups in the correct proportions
• Varying dietary needs of individuals

  • Age
  • Gender
  • Activity levels
  • Health conditions
• Scurvy


  Severe vitamin C deficiency
• Scurvy


  • Caused by lack of vitamin C in diet for over 3 months
  • Symptoms include anemia, exhaustion, spontaneous bleeding, pain in limbs, swelling, gum ulcerations, tooth loss
  • Commonly seen in sailors between 15th to 18th centuries
  • Can be treated with oral or intravenous vitamin C supplements
• Rickets


  Condition in children characterized by poor bone development
• Rickets


  • Symptoms include bone pain, lack of bone growth, soft/weak bones
  • Caused by severe lack of vitamin D
  • Vitamin D required for absorption of calcium into body
  • Treatment is to increase consumption of foods containing calcium and vitamin D or take vitamin D supplements
• Stages of food breakdown in the digestive system

  • Ingestion
  • Mechanical digestion
  • Chemical digestion
  • Absorption
  • Assimilation
  • Egestion
• Functions of the digestive organs

  • Mouth - chewing, mixing with saliva
  • Esophagus - transports food to stomach
  • Stomach - churns and digests food
  • Small intestine - further digestion and absorption
  • Large intestine - absorbs water, stores waste
  • Liver - produces bile
  • Pancreas - produces enzymes
  • Gallbladder - stores and concentrates bile
• Physical digestion

  Breakdown of food into smaller pieces without chemical change
• Physical digestion


  • Increases surface area of food for action of enzymes during chemical digestion
  • Carried out by chewing, churning in stomach, emulsification of fats by bile
• Types of human teeth

  • Incisors - for biting and cutting
  • Canines - for tearing, holding and biting
  • Premolars and molars - for chewing and grinding
• Stomach


  One of the organs of the digestive system
• Stomach


  • Lining contains muscles that contract to physically squeeze and mix food with digestive juices
  • Food is digested within the stomach for several hours
• Emulsification of fats and oils

  Breaking down large drops of fat into smaller ones to increase surface area for lipase enzymes
• Emulsification


  • Bile produced in liver and stored in gallbladder has two roles: 1) neutralize hydrochloric acid from stomach, 2) emulsify fats
• Emulsification is an example of mechanical digestion, not chemical digestion
• Chemical digestion


  Breakdown of large, insoluble molecules into small, soluble molecules
• Emulsification

  The equivalent of tearing a large piece of paper into smaller pieces of paper
• Stages of food breakdown

  1. Ingestion

  2. Mechanical digestion

  3. Chemical digestion

  4. Absorption

  5. Assimilation

  6. Egestion
• Chemical digestion


  The breakdown of large, insoluble molecules into small, soluble molecules
• Amylases


  Enzymes that digest starch into smaller sugars, produced in the mouth and pancreas
• Proteases


  Enzymes that break down proteins into amino acids in the stomach and small intestine
• Lipases


  Enzymes that digest lipids into fatty acids and glycerol, produced in the pancreas
• Hydrochloric acid


  Fluid produced in the stomach that kills bacteria and provides an acidic pH for enzymes
• Low pH in the stomach


  Kills bacteria and provides optimal conditions for pepsin enzyme
• Digestion of starch


  1. Amylase breaks down starch to maltose

  2. Maltase breaks down maltose to glucose
• Digestion of protein


  1. Pepsin breaks down protein in acidic conditions in the stomach

  2. Trypsin breaks down protein in alkaline conditions in the duodenum
• Bile


  • Produced in the liver, stored in the gallbladder, has two main roles:
  • Neutralises hydrochloric acid
  • Emulsifies fats to allow faster lipase action
• Absorption


  The movement of digested food molecules from the digestive system into the blood and lymph
• Most water absorption (around 80%) happens in the small intestine
• Adaptations of the small intestine

  • Very long and highly folded surface with millions of villi to increase surface area
  • Microvilli on the surface of the villus further increase surface area
  • Wall of the villus is one cell thick for faster absorption
  • Well supplied with blood capillaries and lacteals to transport absorbed nutrients