digestive system

• digestion is finished at the small intestine
• bile is a green fluid secreted by the liver and is stored
• bile is added to the first part of the small intestine via the bile duct
• bile breaks down large fat globules into smaller ones which have a greater surface area than 1 large fat globule giving lipase more surface area to act on and chemical digestion is faster
• 1.At the point of 'circular muscle contracting', circular muscles contract making lumen smaller and squeezing food forward.

  2.At the point where the 'food is moved along', circular muscles relax allowing lumen to widen

  
• At the mouth (starch broken down to glucose) , processes of ingestion chemical mechanical digestion take place and in the saliva is the enzyme amylase . Teeth chop up food, salivary glands make saliva and as well as containing carbohydrase it lubricates the food making it easier to swallow
• At the stomach (protein broken down to amino acids), processes of mechanical and chemical digestion take place and the gastric juice contains the enzyme protease. As the stomach churns up the food with gastric juice (mix of hydrochloric acid + protease). This provides optimum pH for protease to work and kills bacteria
• At the pancreas, chemical digestion takes place and the pancreatic juice contains all three enzymes and is added to the first part of the small intestine through the pancreatic duct
• At the small intestine processes of chemical digestion and absorption happen and the intestinal juice contains all 3 enzymes. Digestion is completed her and the small soluble molecules can pass through the intestinal wall by diffusion into the blood stream. Can now be used by body cells
• At the large intestine, processes of absorption of water and egestion take place. Water is reabsorbed to leave semi solid waste called faeces. They are stored in the last part of the large intestine before being egested through the anus
• Bile is secreted into the small intestine where it has two effects:

  • it neutralises the acid - providing the alkaline conditions needed in the small intestine
  • it emulsifies fat - turning large droplets of fat into lots of smaller droplets, thus providing a larger surface area over which the lipase enzymes can work
• small intestine adaptations - 6m long so food can take a long time to pass through so there is more time for absorption
• small intestine adaptations - there are millions of villi so there is a short diffusion distance for the molecules to diffuse from the gut into the blood
• small intestine adaptations - villi have a surface layer, one cell thick - shorter distance for molecules to diffuse from the gut into the blood
• small intestine adaptations - villi containing blood capillaries so this provides a good transport system to all body cells. It also keeps molecules on the 'blood' side at a low concentration so the gradient is maintained
• Absorption in the small intestine

  The small intestine is well adapted to absorb small soluble food molecules across its wall and into the blood stream. The inside has millions of finger like projections called 'villi' that stick out of its wall

  
• pathway of digestion is mouth, through the esophagus, stomach, small and large intestine then leaves through the anus and is absorbed into the bloodstream
• Egestion what remains at the end of the small intestine :

  • water
  • bacteria (living and dead)
  • cells from the lining of the gut
  • indigestible substances - such as cellulose from plant cell walls
• Digestive system - labelling!!

  A) salivary glands

  B) mouth

  C) Oesophagus

  D) Liver

  E) Stomach

  F) Gall bladder

  G) Bile duct

  H) Pancreas

  I) Large intestine

  J) Small intestine

  K) Anus