124. The Aortic Arches

  1. The first pair of aortic arches is formed by the curving of the ventral aorta into the primitive dorsal aorta. This arch is hidden in the mandibular arch and participates in formation of the maxillary artery, and contribute to the external carotid artery
  2. The second pair of aortic arches make their appearance in the middle of week 4. They cross the second branchial arches and give rise to the stapedial and hyoid arteries. (It should be noted that arches I and II regress rapidly and are not seen after day 31)
  3. The third pair of aortic arches make their appearance at the end of week 4. They give rise to the common carotids and proximal portions of the internal carotid arteries. The latter are the short cephalic prolongations of the primitive dorsal aortas and are associated with development and supply of the brain
    1. THE INTERNAL CAROTID ARTERIES are secondarily attached to the cranial portions of the dorsal aortas, which form the remainder of the carotid artery
    2. THE ORIGIN OFTHE EXTERNAL CAROTID ARTERIES is controversial, but in later stages of development, they are found to sprout from aortic arch II (Arch I, however, has been implicated in its developmental contribution)
  4. The fourth pair of aortic arches make their appearance shortly after the third arches, at the end of week 4. Their development is different for the right and left sides
    1. ON THE RIGHT SIDE arch IV forms the proximal portion of the right subclavian artery and is continuous with the seventh segmental artery
      1. The caudal portion of the right primitive dorsal aorta disappears
      2. The distal portion of the subclavian artery forms from the right dorsal aorta and the right seventh intersegmental artery
    2. ON THE LEFT SIDE arch IV persists as the arch of the aorta, which grows significantly and is continuous with the primitive left dorsal aorta.
      1. The left subclavian artery (or seventh segmental) arises directly from the aorta
    3. THE SHORT PORTION of the right primitive ventral aorta, which persists between arches IV and VI, forms the brachiocephalic arterial trunk and the first portion of the aortic arch
  5. The fifth pair of aortic arches: in 50% of embryos, these arches are rudimentary vessels that degenerate with no derivatives. In fact, they may never even develop
  6. The sixth pair of aortic arches make their appearance in the middle of week 5 and give rise to the right and left pulmonary arteries. After pulmonary vascularization is established, the communication with the corresponding primitive dorsal aorta regresses
    1. REGRESSION is total and complete on the right side. The proximal portion of the right arch forms the proximal part of right pulmonary artery; its distal portion degenerates
    2. THE PROXIMAL PORTION OF THE LEFT ARCH persists as the proximal part of the left pulmonary artery
      1. The distal portion of the left arch, in which communication persists with the dorsal aorta until birth, forms the ductus arteriosus and diverts blood from the pulmonary artery to the aort Closure of the ductus arteriosus takes place in the neonatal period, and the functional duct becomes the anatomic ligamentum arteriosum
    3. THE DISTAL PORTIONS OF THE PULMONARY ARTERIES are derived from buds of the sixth aortic arches that grow into the developing lungs. After partitioning of the truncus arteriosus, the pulmonary arteries arise from the pulmonary trunk
  7. Summary of the aortic arches: arch I regresses; arch II regresses; arch III forms the carotid system; arch IV forms the aortic arch (on the left) and the subclavian (on the right); arch V disappears; and arch VI forms the pulmonary arteries and the ductus arteriosus (on the left)

the aortic arches: image #1