Posterior Mediastinum - LO 2
2. Discuss the parietal and visceral branches of the thoracic aorta.
The descending aorta runs from the arch of the aorta (near T4 vertebral level) to its bifurcation into the common iliac aa. (near L4). The descending aorta is divided into thoracic and abdominal parts by the diaphragm (near T12) delimiting the boundary between them.
The thoracic aorta compliments and anastomose with branches of the internal thoracic a. (from first part of subclavian a.) to supply blood to the wall of the thorax, and also supplies elements of the thoracic viscera; thus, the thoracic aorta has both parietal (serving the wall) and visceral branches.
Parietal branches:
Parietal brs. of the thoracic aorta typically exit the vessel posterolaterally, with posterior intercostal aa. typically servicing the 3rd - 11th intercostal spaces, and the subcostal aa. supplies the body wall below the 12th rib. Parietal brs. of the thoracic aorta typically anastomose with branches of the internal thoracic aa. (eg anterior intercostal brs. and musculophrenic brs.) to serve the thoracic wall.
Visceral branches:
Visceral brs. of the thoracic aorta typically exit the vessel anterolaterally to supply structures within the thorax, including the: bronchi, esophagus, elements of the mediastinum, pericardium, and the superior surface of the diaphragm.
Typically, there are three bronchial aa.:
two left bronchial aa., and
one right bronchial a., which may either originate from the right third posterior intercostal a., or from one of the two left bronchial aa.
The bronchial aa. supply the bronchi, tissues of the lung, bronchopulmonary (hilar) lymph nodes, the proximal portion of the esophagus, etc.
Distal to the bronchial aa. are:
mediastinal brs., which serve tracheobronchial lymph nodes and other tissues of the posterior mediastinum,
pericardial brs., which serve the posterior portion of the pericardium,
esophageal aa., which supply the remainder of the esophagus, and
superior phrenic aa., which service the diaphragm.
