Branchial arch
Schematic of developing fetus with first, second and third arches labeled.
Floor of pharynx of human embryo about twenty-six days old.
Gray's	subject #13 65
Carnegie stage	10
MeSH	Branchial+Arches

In the development of vertebrate animals, the pharyngeal arches (also called branchial arches or gill arches in fish) are anlage for a multitude of structures. In humans, they develop during the fourth week in utero as a series of mesodermal outpouchings on the left and right sides of the developing pharynx. In fish, the branchial arches give rise to gills.

[edit] Development

These grow and join in the ventral midline. The first arch, as the first to form, separates the mouth pit or stomodeum from the pericardium. By differential growth the neck elongates and new arches form, so the pharynx has six arches ultimately.

Each pharyngeal arch has a cartilaginous stick, a muscle component which differentiates from the cartilaginous tissue, an artery, and a cranial nerve. Each of these is surrounded by mesenchyme. Arches do not develop simultaneously, but instead possess a "staggered" development.

[edit] Relations

Pharyngeal or branchial pouches form on the endodermal side between the arches, and pharyngeal grooves (or clefts) form from the lateral ectodermal surface of the neck region to separate the arches. ^[1]

The pouches line up with the clefts, and these thin segments become gills in fish.

In mammals the endoderm and ectoderm not only remain intact, but continue to be separated by a mesoderm layer.

[edit] Specific arches

There are six pharyngeal arches, but in humans the fifth arch only exists transiently during embryologic growth and development. Since no human structures result from the fifth arch, the arches in humans are I, II, III, IV, and VI. ^[2]

More is known about the fate of the first arch than the remaining four. The first three contribute to structures above the larynx, while the last two contribute to the larynx and trachea.

[edit] Use in staging

The development of the pharyngeal arches provide a useful morphological landmark with which to establish the precise stage of embryonic development. Their formation and development corresponds to Carnegie stages 10 to 16 in mammals, and Hamburger-Hamilton stages 14 to 28 in the chicken.

[edit] See also

Pattern of the branchial arches. I-IV branchial arches, 1-4 branchial pouches (inside) and/or pharyngeal grooves (outside)
a Tuberculum laterale
b Tuberculum impar
c Foramen cecum
d Ductus thyreoglossus
e Sinus cervicalis

• Aortic arches
• Branchial pouch
• Branchial cleft cyst
• Congenital cartilaginous rest of the neck

[edit] References

1. ^ "Lecture 24. Branchial Apparatus". http://www.med.howard.edu/anatomy/gas/wk7/Lecture%2024.htm. Retrieved 2007-09-09. 
2. ^ "Text for Pharyngeal Arch Development". http://isc.temple.edu/marino/embryology/parch98/parch_text.htm. Retrieved 2007-09-09. 
3. ^ "marshall.edu". http://musom.marshall.edu/anatomy/grosshom/z_devbranc.html. Retrieved 2007-09-09. 
4. ^ ^{a b} Netter, Frank H.; Cochard, Larry R. (2002). Netter's Atlas of human embryology. Teterboro, N.J: Icon Learning Systems. p. 227. ISBN 0-914168-99-1. 
5. ^ ^{a b} Kyung Won, PhD. Chung (2005). Gross Anatomy (Board Review). Hagerstown, MD: Lippincott Williams & Wilkins. ISBN 0-7817-5309-0. 

[edit] External links

• Graham A, Okabe M, Quinlan R (2005). "The role of the endoderm in the development and evolution of the pharyngeal arches". J. Anat. 207 (5): 479–87. doi:10.1111/j.1469-7580.2005.00472.x. PMID 16313389. http://www.blackwell-synergy.com/doi/full/10.1111/j.1469-7580.2005.00472.x?cookieSet=1.