The digestive system

• The body carries out digestion to convert large insoluble food molecules into smaller soluble molecules
• Large molecules like starch and proteins are too large to pass through the walls of the small intestine and into the blood
• Digestion breaks them down into smaller units, or monomers like glucose and amino acids. These are then transported in the blood (in solution in the plasma) to our cells.
• The cells use the glucose for respiration and other monomers for things like building new proteins or cell membranes
• The small intestine is adapted to speed up the diffusion of nutrients into the blood, it has:

  • a very large surface area as it's covered on villi
  • a good blood supply to maintain a steep concentration gradient
  • thin walls for a short diffusion distance
• The alimentary canal is another name for the gut
• The mouth : (Mechanical digestion) - to break down big pieces of food into smaller pieces. (Chemical digestion) - amylase breaks down carbohydrates into maltose (then glucose)
• Oesophagus: the part of the alimentary canal which connects the throat to the stomach. Muscles contract and relax to push food down to the stomach (peristalsis)
• Stomach:

  • Produces hydrochloric acid (makes the pH approx. 2) - this kills pathogens and denatures amylase from the mouth.
  • The enzyme pepsin starts to break protein down into amino acids
  • Muscles contract to churn the stomach contents
• Liver: produces bile, which is stored in the gall bladder and released into the small intestine. It neutralises stomach acid anf emulsifies fats to give them a bigger surfacse area
• Pancreas: produces enzymes - proteases, carbohydrases and lipases that break down proteins, carbohydrates and lipids
• Small intestine: Where most digestion happens - large molecules are broken down into smaller soluble ones by enzymes. the enzymes are made by the pancreas and cells lining the walls of the small intestine. These can then be absorbed through the wallod the small intestine, into the bood. The first part is the duodenum and the last part is the ileum
• Large intestine: Also called the colon, undigested material passes through here, and most water is reabsorbed into the blood.
• Rectum: The last part of the large intestine, where faeces are stored and then passed out of the body through the anus.