Digestivfe system

• Food contains three main nutrients: carbohydrates (eg starch) , protein and lipids (fats) All of these are large molecules which are too large to be absorbed into the bloodstream. So they have to be digested.
• During digestion, large food molecules are broken down into smaller molecules by enzymes. The small molecules can then be absorbed into the bloodstream.
• First, food is chewed in the mouth. Enzymes in the saliva begin to digest the starch into smaller sugar molecules.
• The food then passes down the oesophagus and into the stomach. In the stomach, enzymes begin the digestion of proteins. The stomach also contains hydrochloric acid which helps the enzymes to digest proteins. The food spends several hours in the stomach.
• The churning action of the stomach muscles turns the food into a fluid increasing the surface area for enzymes to digest.
• The fluid now passes into the small intestine. At this point chemicals are released into the small intestine from the liver and the pancreas. The pancreas releases enzymes which continue the digestion of starch and protein. They also start the digestion of lipids
• The liver releases bile which helps to speed up the digestion of lipids. Bile also neutralises the acid released from the stomach. The walls of the small intestine releases enzymes to continue the digestion of proteins and lipids.
• In the small intestine, the small food molecules produced by digestion are absorbed into the bloodstream either by active transport or by diffusion
• Now the fluid makes its way through the large intestine where water is absorbed into the bloodstream. Finally the faeces are released from the body.
• The salivary glands are located in the mouth and produce saliva/ releases digestive juices and the teeth start to break down food