"Entro" refers to the gastrointestinal tract. Enteritis, for example, is inflammation of some portion of the GI tract. Ileitis, inflammation of the ileum, would be a type of enteritis. An enteropathy would be a condition/ pathology of the GI tract which does not include enteritis/ inflammation.
Intestines are called intestines in medical terms. The medical terminology combining form meaning intestines is entero-
organ
Entero - Whole
An enterovirus is one that infects the small intestine. The combining form entero- refers to the small intestine.
The medical root word 'entero' refers to the intestines.
Whole in Spanish is entero, eg: whole chicken = pollo entero
The stomach has the thickest walls and the strongest muscle in all the GI tract organs. : )
The gastrointestinal (GI) system
Actually, the terms "osteoarthritis" and "gastroenterology" do not specifically illustrate the use of a combining vowel; rather, they showcase the use of combining forms. In "osteoarthritis," "osteo-" (bone) and "arthritis" (inflammation of joints) are combined, while "gastroenterology" combines "gastro-" (stomach) and "entero-" (intestine) with "logy" (study of). The combining vowel, typically "o," is often used in medical terminology to connect roots and suffixes, but in these examples, the combining forms are directly linked without a combining vowel.
UC affects the colon, primarily.
Liver
This is because while combining two medical root words one should keep in mind the anatomical arrangement of those root words. Whichever organ comes first anatomically, should be used first. In the above case the gastro i.e. the stomach comes before entero i.e. intestine so only the work gastroenteritis is valid.