digestion vs digestive system

digestion

noun
  • The process, in the gastrointestinal tract, by which food is converted into substances that can be utilized by the body. 

  • The processing of decay in organic matter assisted by microorganisms. 

  • The ability to use this process. 

  • The result of this process. 

  • The assimilation and understanding of ideas. 

  • Dissolution of a sample into a solution by means of adding acid and heat. 

digestive system

noun
  • A system of organs for the purpose of digesting food. 

How often have the words digestion and digestive system occurred in a corpus of books? (source: Google Ngram Viewer )