Thursday 3 June 2010
In the development of vertebrate animals, pharyngeal pouches (or branchial pouches) form on the endodermal side between the branchial arches, and pharyngeal grooves (or clefts) form the lateral ectodermal surface of the neck region to separate the arches.
The pouches line up with the clefts, and these thin segments become gills in fish.
1st branchial pouch
The endoderm lines the future auditory tube (pharyngotympanic " Eustachian " tube), middle ear, mastoid antrum, and inner layer of the tympanic membrane.
2nd branchial pouch
Contributes to the middle ear, palatine tonsils, supplied by the facial nerve.
3rd branchial pouch
The third pouch possesses Dorsal and Ventral wings. Derivatives of the dorsal wings include the inferior parathyroid glands, while the ventral wings fuse to form the cytoreticular cells of the thymus. The main nerve supply to the derivatives of this pouch is Cranial Nerve IX, glossopharyngeal nerve.
4th branchial pouch
Derivatives include the superior parathyroid glands and ultimobranchial body which forms the parafollicular C-Cells of the thyroid gland.
5th branchial pouch
Rudimentary structure, becomes part of the fourth pouch contributing to thyroid C-cells.