bowel vs digestive system

bowel

noun
  • The entrails or intestines; the internal organs of the stomach. 

  • A part or division of the intestines, usually the large intestine. 

  • The (deep) interior of something. 

digestive system

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

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