HUMAN DIGESTION

• Balanced diet

  Humans need to eat a balance diet in order to maintain their health. This should consist of carbohydrates, lipids, proteins, dietary fibre, minerals, vitamins and water.
• Carbohydrate sources

  Bread, cereals, rice, pasta, potatoes
• Protein sources

  Meat, fish, eggs, pulses
• Lipid sources

  Butter, oil, nutes
• Dietary fibre sources

  Vegetables, bran
• Vitamin A sources

  Carrots, green vegetables
• Vitamin C sources

  citrus fruits, broccoli, peppers
• Vitamin D sources

  Margarine, oily fish
• Calcium sources

  Milk
• Iron sources

  Red meat
• Water sources

  Water, juice, milk
• Function of carbohydrates

  High energy source
• Function of proteins

  For growth and repair of tissues
• Function of lipids

  Storage form of energy and for insulation (fat)
• Function of dietary fibres

  To provide roughage to keep food moving through the gut - deficiency causes constipation
• Function of vitamin A

  Needed for vision, especially in the dark, and for growth
• Function of vitamin C

  Helps to absorb iron
• Function of vitamin D

  Helps to absorb calcium
• Function of calcium

  For bone and teeth strength - deficiency can cause rickets (curving of bones)
• Function of iron

  Needed for haemoglobin - deficiency can cause anaemia
• Function of water

  Needed for cell reactions to take place
• Why is age a factor that affects energy requirements?

  • Energy requirements generally increases as we approach adulthood
  • Energy requirements of adults goes down as they age
• Why is activity level a factor that affects energy requirements?

  • If you are more active you will need more energy for movement
• Why is pregnancy a factor that affects energy requirements?

  • Energy requirements will increase in order to support growth of the foetus
  • Energy requirements also need to increase due to the extra mass of the baby
• Alimentary canal

  The passage food moves through once it has been eaten

  • Mouth
  • Oesophagus
  • Stomach
  • Small intestine (duodenum and ileum)
  • Large intestine (colon and rectum)
  • Pancreas
• How is food moved through the gut?

  Peristalsis, the contracting movement of muscles in the alimentary canal that pushes the bolus of food along the digestive tract
• Where is bile produced and where is it stored?

  Produced in the liver and stored in the gall bladder
• What are the roles of bile?

  1. It is alkaline to neutralise the hydrochloric acid which comes from the stomach.
  2. It emulsifies/breaks down large drops of fat (lipids) into smaller ones.
• How is the small intestine adapted for absorption?

  • The ileum in the small intestine is lined with villi (finger-like projections) to maximise absorption of digested soluble molecules into blood
  • Villi have a thin lining, a large network of cappilaries and have a large surface area - all these lead to faster diffusion
• Functions of the mouth

  • Mechanical digestion - teeth break up larger pieces of food into smaller pieces with larger surface area to volume ratio (bolus)
  • Chemical digestion - amylase breaks down starch into glucose
  • Salivary glands produce saliva to lubricate the food bolus so it can be swallowed easily
• Functions of the oesophagus

  • Tube that connects the mouth to the stomach
  • Food bolus moves down due to peristalsis
• Functions of the pancreas

  • Produces carbohydrase, lipase and protease enzymes
  • Secretes enzymes into the stomach and small intestine
• Functions of the stomach

  • Gastric juice is released from the stomach lining when it detects food in the stomach
  • Peristalsis occurs
  • The digested food is now chyme
• What is gastric juice made of?

  • Pepsin - enzyme breaking down proteins
  • Hydrochloric acid - makes stomach acidic in order for pepsin to work and to kill any ingested bacteria
• Functions of the duodenum (small intestine)

  • Carbohydrase, lipases and proteases digest food here
  • Bile is released into the duodenum
  • Peristalsis occurs here
• Functions of the ileum (small intestine)

  • Lined with villi (finger-like projections) to maximise absorption of digested soluble molecules into blood
  • Villi have a thin lining, a large network of capillaries and have a large surface area
• Functions of the large intestine

  • Water is absorbed here, to produce faeces
  • Faeces are stored in the rectum and then removed through the anus
• Carbohydrates (starch):

  • Broken down by carbohydrases
  • Starch --> maltose by amylase
  • Maltose --> glucose by maltase
• Proteins:

  • Broken down by proteases in the stomach and small intestine
  • Proteins --> amino acids
• Lipids:

  • Broken down by lipases
  • Lipids --> glycerol + 3 fatty acids