The digestive system

• Muscle cells can contracts (get shorter)
• Muscle cells contain special protein fibres which can change their length
• Muscle cells are packed full of mitochondria which provide the energy needed for contraction.
• A tissue is a group of cells with a similar structure and function.
• An organ is a group of tissues working together for a specific function e.g. the stomach. The stomach contains muscle tissue and glandular tissue (which releases enzymes)
• Organs are grouped into organ systems which work together to form organisms
• Food contains three main nutrients: Carbohydrates (e.g. starch), protein and lipids (fats)
• Carbohydrates, proteins and lipids are large molecules. They are too large to be absorbed into the bloodstream. So they have to be digested
• During digestion, large food molecules are broken down into small molecules by enzymes. The small molecules can then be absorbed into the bloodstream.
• The digestive system is responsible for breaking down food into smaller molecules that can 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.
• Second, the food passes down the oesophagus 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 churning acting of the stomach muscles turns the food into a fluid increasing the surface area of enzymes to digest.
• The fluid from the stomach 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 for the stomach.
• The walls of the small intestine release enzymes to continue the digestion of protein and lipids.
• In the small intestine, the small food molecules produced by digestion are absorbed into the bloodstream either by diffusion or by active transport.
• the fluid makes its way through the large intestine (after being in the small intestine) where water is absorbed into the bloodstream.
• Finally, the faeces is released from the body.
• 1. In the digestive system, large food molecules are digested into smaller molecules and digested into smaller molecules and then the product of digestion and absorbed into the bloodstream.
  2. Now the products of digestion are then used by the body to build now carbohydrates, lipids and proteins.
  3. Some of the glucose produced is used in respiration.