Monday, 13 June 2016

Pharyngeal Pouches Derivatives at a glance


Mesenchyme for formation of the head region is derived from paraxial mesoderm and lateral plate mesoderm, neural creast and thickened region of ectoderm known as ectodermal placodes.




The most typical feature in development of the hea and neck is formed by the pharyngeal or branchial arches.These arches appear in the fourth and fifth weeks of development and contribute to the characteristic external appearance of the embryo.Initialy they consist of bars of mesenchymal tissue separated by deep cleafts known as pharyngeal ( branchial ) cleft.Simultaneously ,with development of the arches and clefts ,a number of outpocketing ,the pharyngeal gut ,the pharyngeal pouch,appears along the lateral walls of the pharyngeal gut,the most cranial part of the foregut.
The pouch penetrate the surrounding the mesenchyme, but do not establish an open communication with the external clefts. Therefore the term pharyngeal (arch, cleft, and pouch) has been adopted for the human embryo.




The human embryo has five pairs of pharyngeal pouches . The last one of these is atypical and considered as a part of the fourth. Since the epithelial endoderm lining of the pouch gives rise to a number of important organs. the fate of each pouch is given bellow :




Structures developed from pharyngeal pouch

Pouch
Derivatives
1st  pouch
1.       Middle ear cavity(primitive tympanic)
2.      Auditory tube ( from tuubotympanic recess)
3.       Endodermal lining of tympanic membrane
2nd pouch
1.       Palatine tonsil
3rd pouch
1.       Inferior parathyroid gland
2.      Thymus
4th pouch
1.       Superior parathyroid gland
2.      Lateral thyroid element
5th pouch
1.       Ultimobranchial body which later forms the parafollicular cells or C cell of thyroid gland





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*Data are collected and concise only for post graduate student. Pictures are  collected from Google.






*Data are collected from Langman's Medical Embryology

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