PHARYNGEAL ARCHES

Pharyngeal Arches

Pharyngeal pouches

Contents

Nerve supply

Cartilages

Derivatives

Derivatives

Pharyngeal pouches

• Inner endodermal lined outpouchings from the primitive foregut

Pharyngeal pouches

Pharyngeal pouches

DerivativesPharyngeal pouch Derivatives

1st pouch Eustachian tube,tympanic cavity

2nd pouch Palatine tonsil,tonsillar fossa

3rd pouch Inferior parathyroid,thymus glands

4th pouch Superior parathyroid

5th pouch Ultimobranchial body,parafollicular cells of thyroid

Pharyngeal clefts

• Outer ectodermal lined grooves • 4 in number• Only the first cleft remains and contributes to

facial structure• 1st cleft gives rise to external auditory meatus

and its epithelial lining gives rise to eardrum• Rest form the cervical sinus which soon

disappears

WHEN IT GOES WRONG?

When it goes wrong

• Ectopic thymic and parathyroid tissue• Branchial cysts and fistulae• Neural crest craniofacial defects-Treacher-

Collins,DiGeorge,Robin sequence

Questions

• Why are neural crest cells considered very important for craniofacial development?

• What are the derivatives ofMeckel’s cartilage?Reichert’s cartilage?1st pharyngeal cleft?• What is the embryological basis for branchial

cysts and fistulae?