16. Pharyngeal Arches Flashcards
What week of development do the pharyngeal arches develop in?
4th/5th
What germ layer is found in the clefts?
Endoderm
What germ layer is found in the pouches?
Ectoderm
What is derived from the 1st pharyngeal arch?
Meckel’s cartilage
Malleus and incus
What is derived from the 2nd pharyngeal arch?
Stapes
Styloid process
Stylohyoid ligament
Lesser horn of hyoid
What is derived from the 3rd pharyngeal arch?
Greater horn of hyoid
What is derived from the 4th pharyngeal arch?
Upper thyroid cartilage
What happens to the 5th pharyngeal arch?
Disappears
What is derived from the 6th pharyngeal arch?
Rest of the thyroid cartilage
Cricoid cartilage
What is derived from the 1st pharyngeal cleft?
External acoustic meatus
What happens if the 2nd, 3rd and 4th clefts don’t disappear?
Cervical cysts
Presents as lumps under the sternocleidomastoid
What is it called if cervical cysts are open to the surface?
External branchial fistula
What do internal branchial fistulas open into?
Bed of palatine tonsils
What is derived from the 1st pharyngeal pouch?
Middle ear
Eustachian tube
What is derived from the 2nd pharyngeal pouch?
Palatine tonsils
What is derived from the 3rd pharyngeal pouch?
Inferior parathyroid
Thymus
What is derived from the 4th pharyngeal pouch?
Superior parathyroid
Ultimobranchial body
What does the ultimobranchial body become?
Parafollicular cells of the thyroid
What are 2 defects in the 1st arch?
Treacher Collins
Robin Sequence