part_of starts_at ends_at primitive bladder mesenchymal layer of primitive bladder anatomical_structure The mesenchymal layer of primitive bladder (mpbl) (syn: primitive bladder mesenchyme) (TS:19-TS:21) is the mesenchyme surrounding the urothelium of primitive bladder. At TS:19-TS:20, expresses Ptch1 and Gli1. From TS:21, contains smooth muscle cells. The mesenchyme of primitive bladder (and later the bladder) is radially patterned due to differentiation of mesenchymal cells into smooth muscle cells. The layers are defined by their location, differing gene expression profiles and proliferation rates. From TS:20-TS:21 it is divided into inner mesenchyme of primitive bladder (TS:20-TS:21) and outer mesenchyme of primitive bladder (TS:20-TS:21). primitive bladder mesenchyme EMAPA:30876 mesenchyme of urogenital sinus TS19 TS21