part of epithelial cell adult midgut cell of proventriculus adult proventriculus epithelial cell adult midgut epithelial cell adult proventriculus epithelial zone 5 adult proventriculus zone 5 epithelial cell 2024-06-21T10:21:15Z FBbt:00059335 PV5 cell fly_anatomy.ontology Epithelial cell of the fifth zone of the adult proventriculus epithelium (King, 1988). These are very tall columnar cells. Their apical end is drawn out into a cytoplasmic peg which projects into the lumen. They secrete the third layer of the peritrophic membrane (Zhu et al., 2024). There are approximately 1600 of these cells in the adult proventriculus.