The digestive system

• A tissue is a group of cells with a similar structure to function
• an organ is a group of tissues working together for a function
• Biology sizes in order:

  Cell

  Tissue

  Organ

  Organ System

  Organism
• There are 3 main nutrients in food: Carbohydrates (starch), Proteins, and Lipids (fats). All are large molecules that have to be digested.
• During digestion, large molecules are broken down into small molecules by enzymes. Then they are absorbed into the bloodstream.
• The human digestive system

  
• Digestion

  1. Food is chewed in the mouth

  2. Carbohydrase enzymes begin to digest starch into smaller sugar molecules

  3. Food passes down the oesophagus into the stomach

  4. Protease enzymes begin digesting proteins

  5. The hydrochloric acid and churning of stomach muscles turn food into a fluid

  6. The fluid passes into the small intestine

  7. Chemicals from the liver + pancreas go into the small intestine

  8. Enzymes from the pancreas continue starch/protein digestion and begin lipid digestion

  9. The liver releases bile, speeding up digestion and neutralizing stomach acid

  10. The small intestine releases enzymes to continue digestion

  11. Now the small molecules are absorbed into the bloodstream

  12. The fluid makes its way through the large intestine

  13. Here water is absorbed into the bloodstream

  14. Finally, feces is released from the body
• Simple definition of digestion: Large food molecules are digested into smaller molecules. The products of digestion are then absorbed into the bloodstream.
• Products are used to build new carbohydrates, lipids and proteins.
• Glucose is used in respiration.