part of adult midgut region R3ab adult midgut region adult midgut region R3a 2014-06-05T17:29:32Z fly_anatomy.ontology FBbt:00110898 region B of the adult middle midgut Subregion at the anterior end of the adult midgut region R3. It is composed of copper cells (cuprophilic cells) interspersed with interstitial cells. The posterior region R3b is distinguishable from R3a by gene expression.