One word for describing the area of the abdomen is "abdominal" (upper abdominal, lower abdominal. ) The abdomen is often divided into quadants for specific descriptions of areas, RUQ of the abdomen.

Another word is "gastric" : the word gastric usually applies to digestive processes which occur in the abdomen.

Gastrointestinal is another word for a system of the body located in the abdomen.
Abdominal
Abdominal (general), Pelvic, Abdominopelvic, Inguinal (lower abdomen; groin)
Abdominal means pertaining to the abdomen.
Abdominal, however the abdomen are divided into nine regions:

1. epigastric
2. right hypocondriac
3. left hypocondriac
4. right lumbar
5. umbilical
6. left lumbar
7. right iliac
8. hypogastric
9. left iliac