adult midgut constriction adult midgut constriction R3-R4 2014-06-05T17:29:32Z Marianes and Spradling (2013) designate this boundary as a distinct subregion (iron region). One of the two large constrictions of the adult midgut. It corresponds to an area where the midgut abruptly folds and turns up. It is the most dorsal point of the midgut. The cells in this area accumulate ferritin. It separates region 3 (R3) from region 4 (R4). FBbt:00110917 BR3-R4 fly_anatomy.ontology boundary R3-R4