Pharyngeal Arches ppt - غير معروف

Pharyngeal (Branchial) Arches

They are 6 mesodermal thickenings on both sides of pharynx. They starts to appear at the end of 4th week. Arches are covered with ectoderm (externally) and lined with endoderm (internally). Arches are separated from each other by 4 clefts on outer surface which is covered with ectodermal cells. Arches are separated from each other by 5 pouches on inner aspect (cavity of larynx) which are lined with endodermal cells.
Dr. Sherif Fahmy

Structure of each arch

Each arch is composed of mesodermal cells that give rise to bones, cartilages and muscles. Each arch has an arterial supply which is called aortic arch.
Dr. Sherif Fahmy

Each arch has a nerve supply: -Mandibular & Maxillary n. supplies derivatives of 1st arch. -Facial n. supplies derivatives of 2nd arch. -Glossopharyngeal n. supplies derivatives of 3rd arch. -Superior laryngeal br. of vagus supplies derivatives of 4th arch. -Recurrent laryngeal n. supplies derivatives of 6th arch. N.B. Pre-trematic nerve crosses from one arch to other, e.g. chorda tympani n.(branch of facial n.) supplies anterior 2/3 of tongue.

Dr. Sherif Fahmy

Fate of Pharyngeal Arches

Fate of Pharyngeal Pouches

Arch
Ventral part
Dorsal part
First pouch
Occupied by developing tongue.
Tubo-tympanic recess that gives rise to midlle ear & Eustachian tube
Second pouch
Occupied by developing tongue
Palatine tonsile
Third pouch
Thymus gland
Inferior parathyroid gland
Fourth pouch
Unknown
Superior parathyroid gland
Fifth pouch
Ultimo-branchial body which form parafollicular cells in thyroid
Dr. Sherif Fahmy

Fate of Pharyngeal Clefts

Clefts are present on outer surface between the arches, covered with ectoderm. Dorsal part of first cleft forms external auditory meatus and outer layer of ear drum. Downward growth of 2nd arch will cover the other clefts with a space inbetween called cervical sinus. Cervical sinus becomes smaller till it is completely obilterated.

Congenital Anomalies

Ectopic thymic present in neck Ectopic parathyroid tissue especially inferior parathyroid gland. Branchial cyst: Remenant of cervical sinus. Branchial fistula: Remenant of cervical sinus that communicates with skin through extenal fistula, while if it communicates with pharynx it forms internal fistula.