Aortic Arch Formation
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Notes
Aortic Arches
Pharyngeal arches form weeks 4-5; each arch has its own cranial nerve and artery.
Week 5
- Dorsal aortae are fused distally.
- Ventrally, the truncus arteriosus and aortic sac extend cranially.
- Arch arteries 1, 2, 3, 4, and 6 arise from the aortic sac and terminate at the dorsal aortae.
- Be aware that some texts refer to 5th aortic arch arteries; however, even if present, they degenerate early and leave no adult derivatives.
Week 7
- Portions of the dorsal aortae and arches 1 and 2 are degenerating.
- Arch 3 grows bilaterally and gives rise to the common and internal carotid arteries; the external carotid arteries sprout from the third arch.
- The truncus arteriosus and aortic sac are elongated, and are continuous with the fourth arches, which grow asymmetrically:
- The left portion is larger than the right, and is continuous with the remaining dorsal aorta.
- The 6th aortic arch gives rise to the ductus arteriosus and the pulmonary arteries, which will eventually anastomose with arteries developing in the lungs.
- During development, the ductus arteriosus shunts blood from the pulmonary trunk to the aorta, bypassing the lungs; after birth, the ductus arteriosus closes and remains as the ligamentum arteriosum.
Week 8
- Single aorta now comprises ascending, arch, and descending portions.
Notice that the subclavian arteries are asymmetrical, as the right subclavian artery is a division of the brachiocephalic artery.
Aortic arch origins:
- The ascending, proximal arch, and brachiocephalic artery are derivatives of the aortic sac and truncus arteriosus (be aware that some intertextual variation exists).
- The proximal portion of the right subclavian artery arises from the right fourth aortic arch.
- The portion of the aorta between the left common carotid and subclavian arteries is derived from the left fourth aortic arch.
- The descending aorta is derived from the fused dorsal aorta.
- The common carotid artery and proximal portions of the internal carotid arteries are derived from the third aortic arch.
- The rest of the internal and external carotid arteries and the left subclavian artery are not direct derivates of the arches.
- The ductus arteriosus and pulmonary arteries comprise components of the sixth aortic arch.
- The pulmonary trunk, like the proximal aorta, arises from the truncus arteriosus.
- Because of the asymmetrical growth of the aortic arches, the final location of the right and left recurrent laryngeal nerves is also asymmetrical:
Summary of the derivatives of the aortic arches:
- Remnants of the first aortic arches contribute to the maxillary arteries of the face.
- Remnants of the second aortic arches contribute to the stapedial and hyoid arteries.
- The third aortic arches give rise to the common carotid arteries and proximal portions of the internal carotid arteries.
- The left fourth aortic arch gives rise to a portion of the adult aortic arch; the right aortic arch gives rise to the proximal portion of the right subclavian artery.
- The sixth aortic arch gives rise to the pulmonary arteries and ductus arteriosus.
Clinical correlation:
- Patent ductus arteriosus occurs when the vessel persists after birth, allowing left to right blood shunting. The size of the opening determines subsequent heart defects.