diet and digestion

• Mechanical digestion


  1. Breakdown of food into digestible particles mainly by the teeth

  2. Increases the surface area for the enzymatic reactions in the chemical digestion
• Chemical digestion


  Compounds with a high molecular weight (larger molecules) in the food are broken down into small substances that can be absorbed by the body (driven by enzymes)
• Function of the stomach

  • The food stays in the stomach for 4/5 hours and the muscular walls continually pummel the food
  • The food is mixed with enzyme, pepsin, that breaks down proteins contained within it
  • The stomach also produces hydrochloric acid which helps kill bacteria
• Function of the pancreas

  • Produces protease , lipase and amylase
  • These enzymes are released into the small intestines to help digest the food
• Function of the liver

  Produces bile which neutralises stomach acid and emulsifies fats
• Function of the oesophagus


  • After food has been chewed and mixed with saliva in the mouth it enters the oesophagus, which links the throat with the stomach and is surrounded by a ring of muscles that contract and relax at times to push the food down to the stomach
  • This relaxing and contracting of muscles is known as peristalsis
• Food travels by peristalsis in the digestive system
• Function of the small intestine

  • Produces protease, lipase and amylase to complete digestion
  • The food has by now been broken down into small chemicals and is ready to be absorbed out the digestive system
  • Absorbs nutrients
• Function of the large intestine

  • Contains undigested food like fibre
  • Responsible for absorbing all of the excess water
• Function of the rectum

  Where the faeces are stored before being passed down to the anus
• Absorption


  The process by which the products of digestion are taken into the blood to be supplied to the rest of the body
• Adaptations of the small intestine

  • Highly folded surface
  • One cell thick walls
  • Network of blood capillaries
• Highly folded surface


  Increases the efficiency of absorption because it also increases the surface area for the soluble products of digestion to be absorbed
• Walls of the villus being one cell thick


  • Increases efficiency because what is trying to be absorbed only has to pass through a thin wall making it easier for the nutrients to enter
  • There is a short diffusion distance
• Network of blood capillaries

  • A blood vessel is nearby for the food to be absorbed into
  • The product of digestion can be quickly taken away therefore more glucose can be absorbed
  • This increases the overall efficiency of absorption
• carbohydrates:

  needed so the body has enough energy to function

  provide this energy to fuel the body and energy needed for reactions

  keeps other organs working properly and support muscle activity

  provide us with some essential nutrients
• protein

  build new cells in our bodies

  builds tissue

  helps with growth and repair

  helps fight infections and creates antibodies to do so

  vital part of the process that fuels your energy and carries oxygen around in your blood
• lipids(Fats and oils)

  a source of energy

  creates cell membranes as an insulation

  absorbs vitamins such as A,D,E (fat soluble vitamins can only be absorbed with the help of fats)

  energy store
• vitamin A

  helps improve vision in dim light

  keeps skin healthy

  improves and strengthen your immune system

  helps our cells grow and develop
• vitamin C

  helps to make blood cells

  maintains healthy skin, blood vessels, bones and cartilage

  forms and maintains bones

  as an antioxidant, it also supports the immune system
• vitamin D

  keeps cells healthy

  helps wounds heal

  promotes calcium absorption in the gut
• dietary fibre

  keeps the digestive system healthy so waste can move through it fast

  helps to prevent constipation

  high fibre diets can reduce risk of heart disease and stroke
• mineral - iron

  important for the creation of red blood cells, which carry oxygen around the body

  needed for growth and development

  body uses iron to make hemoglobin
• mineral - calcium

  helps keep bones strong and healthy

  makes up structure of teeth and bones

  allows normal body movement by keeping tissue rigid, strong and flexible

  body needs calcium for nerves to carry messages between your brain and every part of your body

  helps body with squeezing and relaxing muscles
• coronary heart disease

  caused by : diet being too high in saturated fat and cholesterol

  effect : fat deposits build up in arteries supplying the heart. this reduces blood flow to heart and muscle cells and can eventually lead to heart attacks
• obesity

  caused by : taking in more energy than is used

  effect : extra energy stored as fat and weight increases. this contributes to development of heart disease/diabetes
• scurvy

  caused by : severe defficiency of vitamin c

  effect : lack of vitamin c will prevent wounds healing properly, causes gums to bleed and teeth to fall out
• kwashiorokor

  caused by : severe deficiency of protein

  effect : leads to fluid retention making stomach appear bloated
• starvation

  caused by : taking in less energy than is used over a long period

  effects : body breaks down energy stores (fat then muscle tissue) leading to severe weight loss
• constipation

  caused by : lack of fibre in the diet

  effects : food lacks bulk for muscles to push food through dietary canal. increases risk of bowel cancer