Digestive system

• digestion is the breakdown of large insoluble food molecules into small soluble molecules to absorb into blood
• fibre is egested from the body as faeces as it is not possible to digest and absorb it into the blood
• Process of the digestive system:

  ingestion --> digestion --> absorption --> egestion
• mechanical digestion physically breaks down food e.g. teeth, stomach churning
• enzymes speed up the process of breaking down large insoluble molecules to small soluble molecules
• acids have low pH which can kill bacteria
• starch is broken down by the enzyme amylase to produce glucose for energy
• proteins are broken down by the enzyme protease to produce amino acids for growth and repair
• fats are broken down by the enzyme lipase to produce fatty acids and glycerol for energy
• biuret is used to test for protein and will turn from blue to lilac
• benedicts is used to test for glucose and will turn from blue to brick red - NEEDS TO BE HEATED STRONGLY
• iodine is used to test for starch and will turn from brown to blue black
• Each of these enzymes are found in ...

  Amylase - small intestine, pancreas, mouth

  Protease - small intestine, pancreas, stomach

  Lipase - small intestine, pancreas
• gall bladder stores bile produced by the liver
• the liver produces and secretes bile
• stomach secretes protease which digests protein
• pancreas secretes lipase, protease and carbohydrase into the small intestine
• small intestine digests and absorbs food
• large intestine absorbs water
• peristalsis is the contraction of muscles behind food to move it through the digestive system
• bile is produced in the liver and stored in the gall bladder
• bile emulsifies fats and increases the pH of the small intestine for lipase
• emulsification is a process that breaks down large fat droplets into small fat droplets to increase surface area, increasing enzyme activity
• mouth

  • teeth mechanically breaks down food
  • saliva contains enzymes which chemically breaks down starch
• stomach

  • stomach acid kills bacteria
  • protease enzymes break down protein
• pancreas

  makes enzymes such as amylase, lipase and protease and releases these to the small intestine
• liver

  makes bile
• gall bladder

  stores bile
• bile duct

  carries bile from gall bladder to small intestine
• small intestine

  • bile from liver emulsifies fats
  • enzymes from pancreas and other enzymes produced by the small intestine break down food
  • small soluble food molecules are absorbed through the walls of the small intestine lined with villi to increase surface area
• large intestine

  absorb water
• the small intestine is adapted for absorption as:

  • it is lined with villi to increase surface area
  • it has a rich blood supply
• evaluating visking tubing as model gut

  mixture of starch, glucose, fats, protein - gut contents

  visking tubing - gut wall

  water - blood
• similarities of model gut

  • food molecules contained in tube
  • food in tube mixture of large and small molecules
  • tube surrounded by liquid containing low concentration of food molecules
• differences of model gut

  • real gut lined with villi
  • real gut surrounded by blood flowing
  • visking tubing does not move food around by muscular contractions
• obesity is caused by a person's energy intake being greater than the energy output
• excess energy is stored as fat
• obesity can contribute to heart disease, high blood pressure, type 2 diabetes, and some cancers
• minerals and vitamins are needed to keep us healthy
• fats and carbohydrates provide energy