The human digestive system

• The digestive system is an organ system in which several organs work together to digest and absorb food
• The breakdown of food is catalysed by enzymes
• In the digestive system, the enzymes used are produced by specialised cells in the glands and gut lining
• Different enzymes catalyse the breakdown of different food molecules
• The salivary glands produce amylase enzymes in the saliva
• Roles of stomach:

  • beats the food with its muscular walls
  • produces protease enzyme, pepsin
  • produces hydrochloric acid to kill bacteria, and to give the right pH for the protease enzyme to work
• Role of liver

  • where bile is produced
  • neutralises stomach acid and emulsifies fats
• Role of gall bladder

  Where bile is stored before released into the small intestine
• Role of pancreas

  Produces protease, amylase and lipase enzymes. Pancreas releases these into the small intestine
• Role of large intestine

  Where excess water is absorbed from the food
• Role of small intestine

  • Produces protease, amylase and lipase enzymes to complete digestion
  • also where the digested food is absorbed out of the digestive system into the blood
• Role of rectum

  where faeces are stored before going through the anus
• A: Salivary glands

  B: Oesophagus

  C: Stomach

  D: Liver

  E: Gall bladder

  F: Pancreas

  G: Small intestine

  H: Large intestine

  
• Digestive enzymes break down large food molecules into smaller soluble molecules that can be absorbed into the bloodstream
• An enzyme is a protein that catalyses chemical reactions in an organism

  • Catalyst: substance that speeds up a chemical reaction without being used up
• An enzyme’s active site is the part of the enzyme that a substrate binds with
• A substrate is a substance in the chemical reaction that the enzyme catalyses
• Enzymes only catalyse specific reactions because an enzyme’s active site is a specific shape.

  • only certain substrates fit the active site so an enzyme can only catalyse specific reactions
• Lock and key method

  • Only a substrate that exactly fits an enzyme’s active site can bind to the enzyme
  • when the substrate binds, the enzyme catalyses the reaction
• Induced fit model

  • An alternative model
  • the active site changes shape to tightly bind to a substrate that’s roughly the right shape
• When an enzyme is denatured:

  • It’s active site changes shape
  • the substrate won’t fit the active site
  • the enzyme can’t catalyse any more reactions
• Two things that causes an enzyme to denature:

  • high temperatures
  • pH value that is too low or too high
• How does changing temperature affect the rate of an enzyme catalyses reaction?

  • As temperature increases, the rate of an enzyme catalysed reaction increases- particles have more kinetic energy
  • if the temperature gets too high, the enzymes denature and rate of reaction decreases 
• The optimum temperature and pH the enzyme has means its which an enzyme works best
• Metabolism: the sum of all reactions happening in a cell or organism
• Carbohydrases

  • Made in salivary glands, pancreas and small intestine
  • breaks down carbohydrates to simple sugars. Amylase is a carbohydrate that breaks down starch into maltose
• Proteases

  • Made in the stomach, pancreas and small intestine
  • breaks down proteins into amino acids
• Lipases

  • Made in the pancreas and small intestine
  • breaks down lipids to glycerol and fatty acids
• • The products of digestion are used to make proteins, carbohydrates and lipids
  • some of the glucose made by digestion is used in respiration
• Role of bile

  • Made in the liver and stored in the gall bladder
  • it's alkaline to neutralise hydrochloric acid from the stomach
  • emulsifies fats to form small droplets increasing the surface area
  • the alkaline conditions and large surface area increase the rate of fat breakdown by lipase