Thoracic Cavity

The thoracic cavity, also known as the chest cavity, is a major body compartment in vertebrates enclosed by the thoracic wall and housing vital organs of the cardiovascular, respiratory, digestive, and nervous systems. Situated between the neck and the abdominal cavity, it provides a rigid yet flexible protective chamber essential for respiration and circulatory function. Its boundaries, subdivisions, and internal contents collectively support some of the body’s most critical physiological processes.

Structural Boundaries and Apertures

The thoracic cavity is encased by the rib cage, thoracic vertebrae, sternum, and associated muscles and fascia. Inferiorly, it is separated from the abdominal cavity by the thoracic diaphragm, a dome-shaped musculotendinous sheet crucial for breathing. Sagittal anatomical images reveal the heart positioned behind the sternum and ribs, with thoracic vertebrae posteriorly and the diaphragm forming the compartment’s lower boundary.
Two main openings provide passage for structures entering and exiting the cavity:

• The superior thoracic aperture (thoracic inlet) opens into the neck and allows the passage of vessels, nerves, and the trachea.
• The inferior thoracic aperture (thoracic outlet) is much larger and is closed off by the diaphragm, with openings that transmit the aorta, inferior vena cava, and oesophagus.

Internal Organisation and Contents

A defining internal division is the mediastinum, the central compartment between the lungs containing the heart, thymus, oesophagus, trachea, major blood vessels, and nerves. The cavity also contains three mesothelium-lined potential spaces: the two pleural cavities and the pericardial cavity.
Major organ systems within the thoracic cavity include:

• Cardiovascular system: heart, thoracic aorta, pulmonary arteries and veins, superior and inferior vena cava, azygos vein.
• Respiratory system: trachea, bronchi, lungs, and the diaphragm.
• Digestive system: thoracic portion of the oesophagus.
• Endocrine and immune structures: thymus gland.
• Nervous system components: paired vagus nerves, sympathetic chains, and the thoracic duct.

The thoracic duct, the principal lymphatic channel of the body, ascends through the cavity and empties into the venous system near the base of the neck.

Physiological Roles

The thoracic cavity facilitates respiration through the mechanical actions of the diaphragm and intercostal muscles, creating pressure changes that enable airflow. It also houses and protects the heart and major vessels, forming the structural foundation for systemic and pulmonary circulation. Neural pathways within the cavity support autonomic regulation of cardiac and respiratory functions.
The pleural membranes and cavities ensure frictionless movement of the lungs during ventilation, while the pericardium stabilises the heart’s position and protects it from excessive motion.

Clinical Significance

Injury or disease affecting the thoracic cavity can have immediate life-threatening consequences due to the vital organs contained within it. A key example is pneumothorax, which occurs when air enters the pleural cavity—often caused by penetrating trauma such as a gunshot or stabbing wound. The resulting loss of negative pressure can lead to partial or complete lung collapse, requiring urgent medical intervention.
Other conditions commonly associated with the thoracic cavity include pleural effusion, pericardial tamponade, thoracic aortic aneurysm, and infections of the mediastinum. Because the cavity transmits major neurovascular structures between the neck and abdomen, injuries involving the spine or upper torso can also compromise thoracic contents.