Atlas of Anatomy
6 Thoracic Cavity
Divisions of the Thoracic Cavity
The thoracic cavity is divided into three large spaces: the mediastinum (p. 76) and the two pleural cavities (p. 102).
Fig. 6.1 Thoracic cavity
Coronal section, anterior view.
Fig. 6.2 Divisions of the mediastinum
Fig. 6.3 Transverse sections of the thorax
Computed tomography (CT) scan of thorax, inferior view.
Arteries of the Thoracic Cavity
The arch of the aorta has three major branches: the brachiocephalic trunk, left common carotid artery, and left subclavian artery. After the aortic arch, the aorta begins its descent, becoming the thoracic aorta at the level of the sternal angle and the abdominal aorta once it passes through the aortic hiatus in the diaphragm.
Fig. 6.4 Thoracic aorta
A tear in the inner wall (intima) of the aorta allows blood to separate the layers of the aortic wall, creating a “false lumen” and potentially resulting in life-threatening aortic rupture. Symptoms are dyspnea (shortness of breath) and sudden onset of excruciating pain. Acute aortic dissections occur most often in the ascending aorta and generally require surgery. More distal aortic dissections may be treated conservatively, provided there are no complications (e.g., obstruction of blood supply to the organs, in which case a stent may be inserted to restore perfusion). Aortic dissections occurring at the base of a coronary artery may cause myocardial infarction.
Veins of the Thoracic Cavity
The superior vena cava is formed by the union of the two brachiocephalic veins at the level of the T2-T3 junction. It receives blood drained by the azygos system (the inferior vena cava has no tributaries in the thorax).
Fig. 6.5 Superior vena cava and azygos system
Fig. 6.6 Azygos system
Lymphatics of the Thoracic Cavity
The body's chief lymph vessel is the thoracic duct. Beginning in the abdomen at the level of L1 as the cisterna chyli, the thoracic duct empties into the junction of the left internal jugular and subclavian veins. The right lymphatic duct drains to the right junction of the internal jugular and subclavian veins.
Fig. 6.7 Lymphatic trunks in the thorax
Anterior view of opened thorax.
Fig. 6.8 Lymphatic pathways in the thorax
Fig. 6.9 Lymphatic drainage by quadrants
Fig. 6.10 Thoracic lymph nodes
Transverse section at level of tracheal bifurcation (T4), inferior view. The thoracic lymph nodes can be divided into three broad groups: nodes of the thoracic wall (pink), pulmonary nodes (blue), and mediastinal nodes (green). For details of lymphatics of the mediastinum, see pp. 100–101.
Nerves of the Thoracic Cavity
Thoracic innervation is mostly autonomic, arising from the paravertebral sympathetic trunks and parasympathetic vagus nerves. There are two exceptions: the phrenic nerves innervate the pericardium and diaphragm (p. 54), and the intercostal nerves innervate the thoracic wall (p. 58).
Fig. 6.11 Nerves in the thorax
Anterior view of opened thorax.
The autonomic nervous system innervates smooth muscle, cardiac muscle, and glands. It is subdivided into the sympathetic (red) and parasympathetic (blue) nervous systems, which together regulates blood flow, secretions, and organ function.
Fig. 6.12 Sympathetic and parasympathetic nervous systems in the thorax