Digestive system

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Digestive system

  • Oesophagus: carries food from mouth to stomach, adapted for transport not absorbtion. It is made of a thick muscular wall.
  • Stomach: a muscular sac with glands that produce enzymes. Stores and digests food using enzymes. The wall is covered in mucus to prevent the stomach from digesting itself.
  • Small intestine: a long muscular tube. Food is further digested by enzymes. The inner walls contain villi, which increase surface area. The villli have microvilli which adapt the small intestine for the absorption of digestion products. 
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Digestive system

  • Large intestine: absorbs water. Food within the intestine becomes drier and thicker, forming faeces. 
  • Rectum: the final section of the intestine. Stores the feaces, before being removed by the anus.
  • Salivary glands: secrete amylase into the mouth to digest starch.
  • Pancreas: produces pancreatic juices. Contains proteases, lipases and amylase.
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What is digestion?

  • Physical and chemical breakdown.


  • large molecules broken down into smaller molecules to provide a larger surface area for chemical digestion. 
  • food is broken down by the teeth, and churned by the stomach walls. 


  • breaks down large, insoluble molecules into smaller, soluble ones. 
  • hydrolysis is the splitting up of molecules by adding water to the chemical bonds that hold them together. 
  • enzymes are specific to a protein.
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  • Carbohydrases: break down carbohydrates into monosaccharides.
  • Lipases: break down lipids into fatty acids.
  • Proteases: break down proteins into amino acids.
  • Amylase: break down starch into maltose.
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Absorption and Assimilation

  • once they have been broken down molecules are absorbed into the blood from the small intestine. 
  • they are carried to different parts of the body and built up into large molecules again.
  • these molecules are then used in body tissues or in a body process. This is called assimilation
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