Aortic arch

The aortic arch, arch of the aorta, or transverse aortic arch (English: /eɪˈɔːrtɪk/) is the part of the aorta between the ascending and descending aorta. The arch travels backward, so that it ultimately runs to the left of the trachea.The arch of aorta can be seen here, with the lungs to either side and emerging from the heart, below.A branch of the vagus nerve, the recurrent laryngeal nerve, passes underneath the arch of aorta. The nerve is seen here. The aortic arch, arch of the aorta, or transverse aortic arch (English: /eɪˈɔːrtɪk/) is the part of the aorta between the ascending and descending aorta. The arch travels backward, so that it ultimately runs to the left of the trachea. At the cellular level, the aorta and the aortic arch are composed of three layers: The tunica intima, which surrounds the lumen and is composed of simple squamal epithelial cells; the tunica media, composed of smooth cell muscles and elastic fibers; and, the tunica adventitia, composed of loose collagen fibers. Innervated by barometric nerve terminals, the aortic arch is responsible for sensing changes in the dilation of the vascular walls, inducing changes in heart rate to compensate for changes in blood pressure. The aorta begins at the level of the upper border of the second sternocostal articulation of the right side, and runs at first upward, backward, and to the left in front of the trachea; then travels backward on the left side of the trachea and finally passes downward on the left side of the body of the fourth thoracic vertebra. At this point the aortic arch continues as the descending aorta.:214 The aortic arch has three branches. The first, and largest, branch of the arch of the aorta is the brachiocephalic trunk, which is to the right and slightly anterior to the other two branches and originates behind the manubrium of the sternum. Next, the left common carotid artery originates from the aortic arch to the left of the brachiocephalic trunk, then ascends along the left side of the trachea and through the superior mediastinum. Finally, the left subclavian artery comes off of the aortic arch to the left of the left common carotid artery and ascends, with the left common carotid, through the superior mediastinum and along the left side of the trachea.:216 An anatomical variation is that the left vertebral artery can arise from the aortic arch instead of the left subclavian artery. The arch of the aorta forms two curvatures: one with its convexity upward, the other with its convexity forward and to the left. Its upper border is usually about 2.5 cm. below the superior border to the manubrium sterni. Blood flows from the upper curvature to the upper regions of the body, located above the heart - namely the arms, neck, and head. Coming out of the heart, the thoracic aorta has a maximum diameter of 40 mm at the root. By the time it becomes the ascending aorta, the diameter should be < 35–38 mm, and 30 mm at the arch. The diameter of the descending aorta should not exceed 25 mm. The arch of the Aorta lies within the mediastinum. The aortic arch is the connection between the ascending and descending aorta, and its central part is formed by the left 4th aortic arch during early development. The ductus arteriosus connects to the lower part of the arch in foetal life. This allows blood from the right ventricle to mostly bypass the pulmonary vessels as they develop.