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Embryo a arch
Arches, pouches, clefts
| Question | Answer |
|---|---|
| Anterior extensions of dorsal aortae into head | Distal 2/3 of ICA |
| Aortic sac of truncus arteriosus | External carotid arteries |
| 1st aortic arch | Regresses at 4 weeks (small portion forms part of maxillary artery) |
| 2nd aortic arch | Regresses (except for very small amount which forms stapedius and hyoid arteries) |
| 3rd aortic arch | Common carotid arteries and proximal 1/3 of ICA |
| Left 4th aortic arch | Part of arch of aorta, btwn left common carotid and left subclavian aa |
| Right 4th aortic arch | Proximal part of right subclavian |
| 5th aortic arch | Transient |
| Proximal left 6th aortic arch | Proximal part left pulmonary artery |
| Distal left 6th aortic arch | Ductus arteriosus |
| Proximal right 6th aortic arch | Proximal right pulmonary artery |
| Distal right 6th aortic arch | Regresses |
| Left subclavian artery forms from | Left 7th intersegmental artery |
| Right subclavian artery forms from | Proximal: right 4th aortic arch Distal: right 7th intersegmental |
| Aortic sac of truncus arteriosus forms | Brachiocephalic artery, proximal arch of aorta |
| What forms arch of aorta | Aortic sac of truncus arteriosus, left 4th aortic arch, left dorsal aorta |
| 1st pharyngeal pouch | Tubotympanic recess--forms middle ear and auditory tube |
| 2nd pharyngeal pouch | Tonsilar fossa and palatine tonsils |
| Dorsal 3rd pouch | Inferior parathyroid |
| Ventral 3rd pouch | Thymus |
| Dorsal 4th pouch | Superior parathyroid |
| Ventral 4th pouch | Ultimobranchial body |
| 1st pharyngeal cleft | External auditory meatus, outer ectodermal eardrum |
| 2nd, 3rd, 4th clefts | No derivatives |
| What happens to clefts 2,3,4 | 2nd arch grows caudally, overlaps 3,4; fuses with epicardial ridge, forming cervical sinus. |