digestive system

• oesophagus 


  carries food from the mouth to the stomach
• stomach 


  a muscular sac with an inner layer/glands that produces enzymes.

  • mechanicfal digestion - churning
  • chemical digestion - enzymes (protease breaks down proteins into amino acids
• ileum 


  a long muscular tube. food is further digested by enzymes produced by its walls and glands. the inner walls are folded into villi, which gives a large surface area. this is further increased by millions of tiny projections called microvilli, on the epithelial cells of the villi
• the large intestine 


  absorbs water
• rectum


  where faeces are stored before being removed via the anus in a process called egestion
• salivary glands 


  situated near the mouth. they pass their secretions via a duct in the mouth. these secretions contain amylase, which hydrolyses starch into maltose
• pancreas


  a large gland situated below the stomach. it produces a secretion called pancreatic juice. this secretion contains protease to hydrolyse proteins, lipase to hydrolyse lipids and amylase to hydrolyse starch
• carbohydrase


  hydrolyse carbohydrates into monosaccharides

  lactase - galactose and glucose

  sucrase - fructose and glucose
• adaptations of the villi

  • villi and microvilli increase surface area
  • mitochondria provide ATP for active transport
  • one cell thick so short diffusion pathway
  • rich network of blood capillaries to maintain a concentration gradient
  • contain muscle so are able to move and churn the contents of the ileum, maintaining a high concentration gradient
• lipid digestion

  • lipids digested into monoglycerides and fatty acids
  • MG and FAs associate with bile salts to produce micelles
  • when micelles make contact with ileum in cell membrane, they break down releasing MGs and FAs which are non-polar so diffuse into cell
  • treansported to smooth ER and joined to make triglycerides
  • transported to golgi apparatus and associate with cholesterol and lipoproteins to form chylomicrons
  • chylomicron is released into lacteal vessel by exocyosis
  • chylomicrons are hydrolysed by enzymes on cell membranes releasing MGs and FAs into the cell
• endopeptidase (protein digestion)


  hydrolyse the peptide bonds between amino acids in the central region of a protein molecule forming a series of peptide molecules
• exopeptidase (protein digestion)


  hydrolyse the peptide bonds on the terminal amino acids of the peptide molecules formed by endopeptidases. in this way they progressively release dipeptides and single amino acids
• dipeptidase (protein digestion)


  hydrolyse the bond between the two amino acids of a dipeptide.