The thoracic section of the aorta begins at the T5 vertebra and extends to the T12 level at the diaphragm, initially progressing through the mediastinum to the left of the spinal column. Throughout its course in the thoracic segment, the thoracic aorta emits various offshoots known collectively as visceral and parietal branches. The branches that predominantly supply blood to visceral organs are termed visceral branches and include bronchial, pericardial, esophageal, and mediastinal arteries, each named for the tissues they nourish.
Each bronchial artery, typically two on the left and one on the right, delivers systemic blood to the lungs and visceral pleura, apart from the blood directed to the lungs for oxygenation through the pulmonary circuit. The bronchial arteries accompany the respiratory branches from the bronchi to the bronchioles. There is a significant, though not complete, mixing of systemic and pulmonary blood at connection points in the smaller branches of the lungs. This might appear paradoxical—the merging of systemic arterial blood, rich in oxygen, with pulmonary arterial blood, deficient in oxygen—but the systemic vessels also carry nutrients to the lung tissue, similar to their function elsewhere in the body. The mixed blood drains into the standard pulmonary veins, while the distinct bronchial artery branches drain into the bronchial veins.
Each pericardial artery supplies blood to the pericardium, the esophageal artery to the esophagus, and the mediastinal artery to the mediastinum. The other branches of the thoracic aorta, labeled as parietal or somatic branches, include the intercostal and superior phrenic arteries. Each intercostal artery supplies the muscles of the thoracic cavity and the spinal column, and the superior phrenic artery nourishes the upper surface of the diaphragm.
