Digestive System

Digestive System

1. Mouth

   • adds saliva, breaks food into small pieces
   • Oesophagus
     • squeezes food towards stomach, connects mouth and stomach
     • Stomach
       • Churns food up with acid, adds protein-digesting enzymes
       • Small intestine
         • contains digestive enzymes made by the pancreas, allows nutrients to pass through the walls into the blood
         • Pancreas
           • makes digestive enzymes, secretes enzymes into small intestine
           • Large intestine
             • water passes through it's walls into the blood, undigested food passes along this tube
             • Liver
               • makes bile, processes nutrients
               • Gall bladder
                 • releases bile into small intestine when needed, stored bile made by liver

2. Chemical and mechanical processes

3. enzymes speed up chemical reactions

   • Carbohydrases
     • found in mouth, turns starch into glucose
       • e.g. amylase
   • Proteases
     • found in stomach, turns protein into amino acids
       • e.g. pepsin
   • Lipases
     • found in s. intestine, turns fats and oils into fatty acids and glycerol
       • e.g. Lipase

4. Bile

   • strongly alkaline, neutralises stomach acid, ensures optimum conditions for enzymes in s.intestine to work
   • contains salts that break down fats and oils into small droplets
     • Emulsification
       • increases surface area of fats and oils to speed up their digestion

5. Absorption in the small intestine

   • inside wall is thin with large surface area
     • absorption happens quickly and efficiently
     • lined with villi
       • increases surface area, more nutrients absorb faster
         • increases rate of diffusion
       • lacteals
         • take away fat from s.i. to ensure there's a difference in concentration
           • increases rate of diffusion
       • blood capillaries
         • take blood to different vessel, ensures there's a concentration gradient
           • increases rate of diffusion
       • One cell thick
         • less distance for nutrients to travel
           • absorption is quicker

6. Functional foods

   • have health-promoting benefits more than basic nutritional value
     • probiotics
       • contain bacteria to maintain healthy digestive system
         • Bifidobacteria
     • prebiotics
       • contain added sugars that "feed" bacteria in alimentary canal
         • Oligosaccharides
     • Plant stanol esters
       • come from plant stanols
         • found naturally in food such as wheat and maize
           • clinically proven to reduce absorption of cholesterol