bowel vs internal organ

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. 

internal organ

noun
  • An organ, such as the heart or colon, that is entirely within the confines of the body. 

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