Branchial arch

Image:Gray41.png

The branchial arches, also known as pharyngeal arches, develop during the fourth and fifth week in uteroas a series of mesodermaloutpouchings on the left and rightsides of the developing pharynx. These grow and join in the ventral midline. The first or mandibular arch, as the first to form, separates the mouth pit or stomodeumfrom the pericardium. By differential growth the neck elongates and new arches form, so the pharynx has six arches ultimately. Pharyngeal or branchial pouches form on the endodermalside between the arches, and pharyngeal grooves (or clefts) form from the lateral ectodermalsurface of the neckregion to separate the arches. The pouches line up with the clefts, and these thin segments become gillsin fish. In mammals the endoderm and ectoderm not only remain intact, but continue to be separated by a mesoderm layer.

Each pharyngeal arch has a cartilaginousbar, a musclecomponent which differentiates from the cartilagenous tissue, an artery, and a cranial nerve.

There are 6 pharyngeal arches. More is known about the fate of the first arch than the remaining 5. The first three contribute to structures above the larynx, while the last three contribute to the larynxand trachea.

First pharyngeal arch

• Also called the "mandibular arch". Follow the link (above) for more information.

Second pharyngeal arch

• Also called the "hyoid arch"
• Skeletal contributions
  • Stapes, styloid process, hyoid
• Muscular contributions
  • Muscles of facial expression, buccinator, platysma, stapedius, stylohyoid, digastricposterior belly
• Nerve
  • Facial nerve, or the 7th cranial nerve

Third pharyngeal arch

• Skeletal contributions
  • Hyoid
• Muscular contributions
  • Stylopharyngeus
• Nerve
  • Glossopharyngeal nerve, the 9th cranial nerve

Fourth to sixth pharyngeal arches

• Skeletal contributions
  • thyroid cartilage, cricoid cartilage, epiglottic cartilage, arytenoid cartilages
• Muscular contributions
  • intrinsic muscles of larynx, pharynx; levator palati
• Nerve
  • Vagus nerve, the 10th cranial nerve.

Branchial pouches

First pouch

• This is the only pouch in which the endoderm and ectoderm remain close together, as the tympanic membrane. There is minimal mesoderm in the tympanic membrane.
• The endoderm becomes the auditory tube, middle earand mastoid antrum.
• The ectoderm becomes the external acoustic meatus

Second pouch

• Contributes to the middle ear, tonsils, supplied by the glossopharyngeal nerve.

Third pouch

• Derivatives include the inferior parathyroid glandsand thymus

Fourth pouch

• Derivatives include the superior parathyroid glands

Fifth pouch

• Regresses to form the ultimobranchial bodywhich gives rise to calcitoninsecreting parafollicular (C) cells in the thyroid gland.

References

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• McMinn, R., 1994. Last's anatomy: Regional and applied (9th ed).

This article is licensed under the GNU Free Documentation License.
It uses material from the http://en.wikipedia.org/wiki/Branchial+arch Wikipedia article Branchial arch.