part of epithelial cell adult midgut cell of proventriculus adult proventriculus epithelial cell adult midgut epithelial cell adult proventriculus epithelial zone 4 adult proventriculus zone 4 epithelial cell 2024-06-21T10:20:39Z PV4 cell FBbt:00059334 fly_anatomy.ontology Epithelial cell of the fourth zone of the adult proventriculus epithelium (King, 1988). These cells are short to cuboidal columnar cells with long apical microvilli that project loosely into the proventriculus lumen. They secrete the second layer of the peritrophic membrane (Zhu et al., 2024). There are approximately 200 of these cells in the adult proventriculus.