Arch of aorta

Where is the aortic arch?

It lies in the superior mediastinum. As it leaves the ascending aorta it runs a little backward and to the left of the trachea. (StatPearls, Thorax, Heart Aorta and Thorax, Aortic Arch)

On a chest radiograph the arch shows as the aortic knob. (StatPearls, Thorax, Heart Aorta)

What are the branches of the aortic arch?

It has three major branches, in order: the brachiocephalic artery, the left common carotid artery and the left subclavian artery. OpenStax classes each as an elastic artery, while StatPearls calls the common carotids large muscular arteries. (OpenStax A&P 2e, 20.5; StatPearls, Thorax, Heart Aorta, Head and Neck, Anterior: Common Carotid Arteries and Abdomen and Pelvis: Aorta)

The brachiocephalic trunk supplies the right arm and the right side of the head and neck, the left common carotid the left side of the head and neck, and the left subclavian the left arm. (StatPearls, Thorax, Aortic Arch)

The last stretch of the arch, just past the origin of the left subclavian artery, is the aortic isthmus. (StatPearls, Thorax, Heart Aorta)

What does the aortic arch do?

StatPearls places baroreceptors in the wall of the arch. They respond to stretch and signal the brainstem through the vagus nerve, one of the main ways the body prevents quick, large swings in blood pressure. (StatPearls, Thorax, Aortic Arch)

Chemoreceptors called aortic bodies monitor the oxygen and carbon dioxide in the blood, and a change in either gas signals the brainstem to adjust breathing. (StatPearls, Thorax, Aortic Arch)

What is the ligamentum arteriosum?

Before birth the ductus arteriosus joins the pulmonary trunk to the aorta, so blood from the right ventricle can bypass the lungs. After birth it closes, and its remnant is the ligamentum arteriosum. (OpenStax A&P 2e, 20.6; StatPearls, Thorax, Heart Ductus Arteriosus)

The left recurrent laryngeal nerve passes under the arch, beside the ligamentum arteriosum, then enters the groove between the trachea and the esophagus. (StatPearls, Thorax, Mediastinum Superior and Great Vessels)

Coarctation of the aorta, a narrowing present from birth, usually sits where the ductus arteriosus joined the aorta, now marked by the ligamentum arteriosum. (OpenStax A&P 2e, 19.1; StatPearls, Coarctation of the Aorta)

How often does the arch branch differently?

The usual three branch pattern is present in about 80% of people. The commonest variant, seen in about 14%, is the bovine arch, in which both carotid arteries share a trunk with the right subclavian. StatPearls (Abdominal Aorta) calls the name a misnomer, since cattle branch differently. (StatPearls, Thorax, Brachiocephalic (Right Innominate) Arteries and Abdomen and Pelvis: Abdominal Aorta)

Where the sources differ

The sources use different landmarks for the end of the arch. OpenStax ends it at the disc between the fourth and fifth thoracic vertebrae, StatPearls (Aortic Arch) has it turn down at the fourth thoracic vertebra, and StatPearls (Heart Aorta) says it begins and ends at the level of the second rib. (OpenStax A&P 2e, 20.5; StatPearls, Thorax, Aortic Arch and Thorax, Heart Aorta)

The sources place the aortic receptors differently. StatPearls (Aortic Arch) puts the baroreceptors in the wall of the arch and the chemoreceptors, the aortic bodies, on the arch. OpenStax puts the aortic baroreceptors and chemoreceptors in the aortic sinuses of the ascending aorta, just above the aortic valve. (StatPearls, Thorax, Aortic Arch; OpenStax A&P 2e, 20.5)