The correct answer is C. Each pharyngeal arch contains mesoderm. Some of this mesoderm gives rise to blood vessels that are within the pharyngeal arch. These blood vessels are called aortic arches.
- Arch 3 gives rise to an aortic arch that contributes to the common carotid artery and the internal carotid artery bilaterally.
- Arch 4 gives rise to an aortic arch that contributes to the arch of the aorta on the left side and the right subclavian artery on the right side.
The internal carotid arteries branch into the middle and anterior cerebral arteries that form the anterior circulation of the brain. These supply the frontal, parietal and temporal lobes of the brain. The subclavian arteries give rise to the vertebral arteries that join to form the vertebrobasilar or posterior circulation of the brain. These supply the brain stem, cerebellum, and occipital lobe. The anterior and posterior circulations are linked by the posterior communicating arteries to form the circle of Willis.
Pharyngeal arches 1 (choice A) and 2 (choices A and B) give rise to aortic arches that contribute to the maxillary artery and the stapedial artery, respectively.
Arch 5 (choice D) degenerates early in fetal development and therefore has no corresponding aortic arch. Arch 6 (choice E) gives rise to an aortic arch that contributes to the pulmonary artery and the ductus arteriosus on the left and the pulmonary artery on the right.
*Nerves are not derived from pharyngeal arch; they grow into the arch.
This is a multi-step question.
What is the question asking?
Which pharyngeal arches contain blood vessels that develop into the arteries that supply blood to the brain?
What is the first step?
The first step is to determine which adult blood vessels supply blood to the brain. The brain receives its blood supply from the internal carotid arteries (anterior circulation) and vertebral arteries (posterior circulation). The vertebral arteries are branches of the subclavian arteries.
What is the next step?
The next step is to determine which embryonic pharyngeal arches contain arteries that become these arteries that supply the brain. The internal carotid artery arises from the third aortic arch. The subclavian artery, which gives rise to the vertebral artery, arises from the fourth aortic arch.
Can other answers be eliminated?
Any choice that includes a pharyngeal arch other than the third and fourth arches can be eliminated.
- The first arch (choice A) degenerates.
- The second arch (choices A and B) degenerates.
- The fifth arch (choice D) does not exist.
- The sixth arch (choice E) contains an artery that becomes the pulmonary artery.
What is the single best answer and why?
The third and fourth arches (choice C) contain arteries (aortic arches) that develop into the carotid (common and Internal) artery and the aortic arch and subclavian arteries, respectively. The brain receives its blood supply from the internal carotid artery (third arch) and the vertebral arteries, which are branches of the subclavian arteries (fourth arch).
MedEssentials (4th Ed.): pp. 428
First Aid (2019): pp. 605.1
First Aid (2018): pp. 601.1
First Aid (2017): pp. 587.1
