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.
Comment:
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]; [homology-note] "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]" xsd:string {date_retrieved="2012-09-17", external_class="VHOG:0001203", ontology="VHOG", source="DOI:10.1111/j.1469-7580.2005.00472.x Graham A, Okabe M, Quinlan R, The role of the endoderm in the development and evolution of the pharyngeal arches. J Anat (2005)", source="http://bgee.unil.ch/"}