20.5 Circulatory pathways  (Page 6/162)

Thoracic aorta and major branches

The thoracic aorta begins at the level of vertebra T5 and continues through to the diaphragm at the level of T12, initially traveling within the mediastinum to the left of the vertebral column. As it passes through the thoracic region, the thoracic aorta gives rise to several branches, which are collectively referred to as visceral branches and parietal branches ( [link] ). Those branches that supply blood primarily to visceral organs are known as the visceral branches    and include the bronchial arteries, pericardial arteries, esophageal arteries, and the mediastinal arteries, each named after the tissues it supplies. Each bronchial artery    (typically two on the left and one on the right) supplies systemic blood to the lungs and visceral pleura, in addition to the blood pumped to the lungs for oxygenation via the pulmonary circuit. The bronchial arteries follow the same path as the respiratory branches, beginning with the bronchi and ending with the bronchioles. There is considerable, but not total, intermingling of the systemic and pulmonary blood at anastomoses in the smaller branches of the lungs. This may sound incongruous—that is, the mixing of systemic arterial blood high in oxygen with the pulmonary arterial blood lower in oxygen—but the systemic vessels also deliver nutrients to the lung tissue just as they do elsewhere in the body. The mixed blood drains into typical pulmonary veins, whereas the bronchial artery branches remain separate and drain into bronchial veins described later. Each pericardial artery    supplies blood to the pericardium, the esophageal artery    provides blood to the esophagus, and the mediastinal artery    provides blood to the mediastinum. The remaining thoracic aorta branches are collectively referred to as parietal branches    or somatic branches, and include the intercostal and superior phrenic arteries. Each intercostal artery    provides blood to the muscles of the thoracic cavity and vertebral column. The superior phrenic artery    provides blood to the superior surface of the diaphragm. [link] lists the arteries of the thoracic region.

Arteries of the thoracic and abdominal regions