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Arteries found in the thorax.
Hey everyone! This is Nicole from Kenhub, and in this tutorial, we're going to be looking at the arteries that supply the organs and internal structures of the thorax.
The arteries of the thorax all arise from the aorta so it would be natural for us, of course, to begin there. And the aorta – the largest blood vessel in the body – arises directly from the heart which is also located in the thoracic cavity. And after arising from the heart, the aorta descends posterior to the heart through the thoracic cavity and continues into the abdominal cavity where it terminally bifurcates at approximately the level of the fourth lumbar vertebra, L4.
And, of course, the aorta can be divided into three parts. Initially, there is the very short ascending aorta which arises from the left ventricle of the heart, and the ascending aorta produces no branches. Continuous with the ascending aorta is the aortic arch which gives off three branches, and continuous with the aortic arch is the descending aorta. Shown in green is the thoracic portion of the descending aorta called the thoracic aorta, and as it descends, it produces several branches. Inferior to the diaphragm, the thoracic aorta is continuous with the abdominal aorta which will not be discussed in this tutorial.
And so now we've introduced these parts of the aorta to you, let's now jump to the branches arising from the second part of the aorta – the aortic arch. And as you can see in the image, the aortic arch ascends from the heart to the left aspect of the trachea, crosses over the left main bronchus and descends posterior to the left aspect of the esophagus. And as we mentioned previously, there are three important arteries that arise from the aortic arch and these are the brachiocephalic trunk, the left common carotid artery, and the left subclavian artery.
And of these, we're going to start with the brachiocephalic trunk which we can see highlighted in green on our image. And as you can probably guess from its direction moving superiorly and laterally, it's mainly involved in supplying blood to the right arm, head and neck and it achieves this through two branches – the right common carotid artery which courses superiorly within the right carotid sheath to supply the right side of the head and the neck and the right subclavian artery which is continuous with the right axillary artery past the lateral border of the right first rib.
And the right subclavian artery gives rise to three of its own branches – the right internal thoracic artery which subsequently gives off thymic, mediastinal and anterior intercostal branches in addition to the pericardiophrenic and musculophrenic arteries of the right side, the right vertebral artery which together with the left vertebral artery forms the basilar artery supplying the posterior portion of the Circle of Willis, and the right thyrocervical trunk which gives off the ascending cervical, the inferior thyroid, the dorsal scapular and suprascapular arteries of the right side.
While the right common carotid artery rises as a branch of the brachiocephalic trunk, the left common carotid artery arises directly from the aortic arch. It courses superiorly within the left carotid sheath supplying the left side of the head and neck. Similarly, while the right subclavian artery arises as a branch of the brachiocephalic trunk, the left subclavian artery highlighted in green arises directly from the aortic arch. And the left subclavian artery exits the thoracic cavity via the superior thoracic aperture between the anterior and middle scalene muscles. Once the left subclavian artery passes the lateral border of the first rib, it continues as the left axillary artery which supplies the left upper limb.
And let's now move on to the final part of the aorta – the descending aorta. Remember that the thoracic part of the descending aorta is called the thoracic aorta. It descends through the thoracic cavity posterior to the esophagus and anterior to and slightly to the left of the thoracic vertebral column. And the thoracic aorta gives off visceral branches primarily responsible for supplying the thoracic organs, and these branches are the bronchial arteries, the esophageal arteries, the mediastinal arteries which supply the area highlighted, and the pericardial arteries which supply the dorsal pericardium in the highlighted area.
The thoracic aorta also gives rise to the following parietal branches which supply the muscles of the thorax, and these branches are the posterior intercostal arteries, the superior phrenic arteries which course along the superior surface of the diaphragm, and the paired subcostal artery.
And just a last note that's important to mention, at approximately the level of the twelfth thoracic vertebra – T12 – the thoracic aorta enters the abdominal cavity through the aortic hiatus of the diaphragm and becomes the abdominal aorta.