Human nutrition

• Food groups in a balanced diet

  • Carbohydrates
  • Proteins
  • Lipids
  • Vitamins
  • Minerals
  • Dietary Fibre
  • Water
• Scurvy is the name for a severe vitamin C deficiency
• Scurvy


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


  • Condition in children characterised by poor bone development
  • Symptoms include bone pain, lack of bone growth, soft, weak bones (sometimes causing deformities)
  • Caused by severe lack of vitamin D
  • Vitamin D is required for the absorption of calcium into the body
  • Vitamin D mostly comes from exposure to sunlight but can also be found in some foods (fish, eggs and butter)
  • Treated by increasing consumption of foods containing calcium and vitamin D or by taking vitamin D supplements
• Organs of the digestive system

  • Mouth
  • Esophagus
  • Stomach
  • Small intestine
  • Large intestine
  • Rectum
  • Anus
• Stages of food breakdown

  1. Ingestion

  2. Mechanical digestion

  3. Chemical digestion

  4. Absorption

  5. Assimilation

  6. Egestion
• Functions of the digestive organs


  • Mouth - chewing, mixing with saliva
  • Esophagus - transporting food to stomach
  • Stomach - churning and digesting food
  • Small intestine - further digestion and absorption of nutrients
  • Large intestine - absorption of water, storage of waste
  • Rectum - temporary storage of waste
  • Anus - elimination of waste
• Physical digestion is the breakdown of food into smaller pieces without chemical change to the food molecules
• Types of human teeth

  • Incisors - chisel-shaped for biting and cutting
  • Canines - pointed for tearing, holding and biting
  • Premolars and molars - larger, flat surfaces with ridges at the edges for chewing and grinding up food
• The stomach


  • Contains muscles that contract to physically squeeze and mix the food with digestive juices
  • Food is digested within the stomach for several hours
• Bile has two main roles: to neutralise the hydrochloric acid from the stomach, and to break down large drops of fat into smaller ones (emulsification)
• Emulsification is a mechanical digestion process, not a chemical digestion process
• Stages of chemical digestion

  1. Ingestion

  2. Mechanical digestion

  3. Chemical digestion

  4. Absorption

  5. Assimilation
• Emulsification


  The equivalent of tearing a large piece of paper into smaller pieces of paper
• Emulsification is an example of mechanical digestion, not chemical digestion
• Chemical Digestion


  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
• Role of chemical digestion

  • To produce small soluble molecules that can be absorbed
• Amylases


  Enzymes that digest starch into smaller sugars
• Digestion of starch

  1. Amylase secreted in mouth and duodenum

  2. Amylase digests starch to maltose

  3. Maltase digests maltose to glucose
• Proteases


  Enzymes that break down proteins into amino acids
• Digestion of proteins

  1. Pepsin in stomach breaks down protein in acidic conditions

  2. Trypsin in duodenum breaks down protein in alkaline conditions
• Lipases


  Enzymes that digest lipids into fatty acids and glycerol
• Hydrochloric acid


  Kills bacteria and provides acidic pH for enzymes in stomach
• Low pH in stomach is helpful as it kills bacteria and provides optimum conditions for pepsin
• Digestion of starch (extended)

  1. Amylase secreted in mouth and duodenum

  2. Amylase digests starch to maltose

  3. Maltase digests maltose to glucose
• Digestion of proteins (extended)

  1. Pepsin in stomach breaks down protein in acidic conditions

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

  Produced in liver, stored in gallbladder, has two main roles:

  1. Neutralise stomach acid

  2. Emulsify fats
• Absorption


  Movement of digested food molecules from digestive system into blood and lymph
• Water absorption

  Mainly in small intestine, some in colon
• Adaptations of small intestine

  • Long and highly folded surface with millions of villi to increase surface area for faster and more efficient absorption

  Microvilli on villi further increase surface area

  Wall of villi is one cell thick for short distance of absorption

  Well supplied with blood capillaries and lacteals to transport absorbed nutrients