part of part of has part has part develops_from embryo pharyngeal arch endoderm of foregut pharyngeal pouch A conserved feature of all vertebrate embryos is the presence of a series of bulges on the lateral surface of the head, the pharyngeal arches; it is within these structures that the nerves, muscles and skeletal components of the pharyngeal apparatus are laid down. The pharyngeal arches are separated by endodermal outpocketings, the pharyngeal pouches.[well established][VHOG] AAO:0011113 An internal pocketing of pharyngeal endoderm that contacts a region of ectoderm (a pharyngeal cleft) and interdigitates in the anterior and posterior directions with the pharyngeal arches. EFO:0003627 EHDAA:1086 EHDAA:1669 EHDAA:579 EHDAA:617 EMAPA also includes a distinct pouch endoderm EMAPA:32752 FMA:293063 Outpocketings of pharyngeal endoderm that interdigitate with the neural crest derived pharyngeal arches. The pouches later fuse with the surface ectoderm to form the gill slits. Crump et al, 2004.[TAO] TAO:0001106 The pouches are polarized structures. For example, whereas the rostral half of each pouch expresses Bmp-7, the caudal half expresses FGF-8 and the dorsal aspect of each pouch is marked via its expression of Pax-1. each pouch has an individual sense of identity. Shh expression is a prominent early feature of the caudal endoderm of the second arch, and individual pouches mark the anterior limits of expression of Hox genes within the pharyngeal endoderm; Hox-a2 has a rostral boundary at the second pouch, Hox-a3 at the third pouch and Hox-a4 at the most caudal pouch[PMID:16313389] UBERON:0004117 UMLS:C0231067 VHOG:0001203 XAO:0000282 ZFA:0001106 branchial pouch pharyngeal pouches uberon visceral pouch visceral pouches upper respiratory tract epithelium embryonic tissue early pharyngeal endoderm pharyngeal arch system