Thorax

The thorax (chest) is the body cavity between the root of the neck and the abdomen. The thoracic cavity houses many vital organs, such as the heart, lungs (pleura), esophagus, trachea, thymus gland, breasts, and the great vessels(1).

The bony rib cage surrounds the thorax. This structure, which includes the thoracic vertebrae and 12 pairs of ribs, is supported by muscles and ligaments. The thorax can be split into several components that contain important structures: the thoracic wall, thoracic cavity, neurovasculature (arteries and veins), and internal organs.

Thoracic Wall

The chest wall (thoracic wall) consists of a skeletal framework, muscles, and neurovasculature that form a strong and flexible cage(2).

The thoracic wall protects the thoracic cavity contents and generates the negative pressure necessary for respiration(3).

The two major openings of the thorax are the superior thoracic aperture and the inferior thoracic aperture. The superior thoracic aperture opens towards the neck. Meanwhile, the diaphragm covers the inferior thoracic aperture almost completely, separating it from the abdominal cavity. The thoracic skeleton consists of the sternum, 12 pairs of ribs, 12 thoracic vertebrae, and interconnecting joints. These structures form the skeletal scaffold of the thorax(4).

Meanwhile, the main thoracic joints include the intervertebral discs, sternocostal, sternoclavicular, costovertebral, costochondral, and interchondral joints. Intercostal spaces are anatomical spaces that run between every two adjacent ribs. Each space contains intercostal muscles (external, internal, and innermost) and the intercostal neurovascular bundle (intercostal vein, artery, and nerve)(5).

The muscles of the thorax are responsible for breathing actions. Other thoracic muscles also form the thoracic wall to contribute to the general movement of the trunk, neck, and upper limbs(6).

These muscles include the transversus thoracis, subcostals, levatores costarum, serratus posterior superior, and serratus posterior inferior muscles. They all attach to the ribs and their cartilages to provide further support and strength for the thorax(7).

Thoracic Cavity

The thoracic wall encloses a cavity or space filled with various anatomical structures. Due to numerous structures present in the thoracic cavity, several compartments aid in the structures’ localization(8).

The division of the thoracic cavity is known as the mediastinum. It is further divided into the superior, anterior, middle, and posterior mediastinal cavities. The thoracic cavity communicates with the neck through the superior thoracic aperture. Meanwhile, the inferior thoracic aperture allows communication with the abdominal cavity through anatomical spaces piercing the diaphragm(9).

Additionally, the thoracic cavity’s inferior boundary is the respiratory diaphragm. This boundary separates the thoracic and abdominal cavities(10).

There are various organs, nerves, thoracic blood vessels, and lymph nodes inside each cavity and compartment.

Neurovasculature

The great vessels of the thorax are the aorta, superior vena cava, inferior vena cava, pulmonary artery, and pulmonary veins. Several major veins and arteries travel through the thorax and originate from the main artery (aorta)(11).

The aorta arises from the heart’s left ventricle and arches superiorly and posteriorly. Near its origin, the aorta supplies blood to the heart through the left and right coronary arteries. The major veins of the thorax collect all the deoxygenated blood from the muscles and organs and bring them into the superior vena cava(12).

The three largest thoracic arteries are the brachiocephalic trunk, left common carotid artery, and left subclavian artery. Visceral arteries that also supply blood to various thoracic organs include bronchial, esophageal, pericardial, and small mediastinal arteries(13).

Internal Organs

The thorax contains vital organs and structures, including the heart, lungs, thymus, esophagus, and trachea. One of the most vital organs situated in the thorax is the heart. This organ receives blood directly through coronary circulation and consists of four chambers (two atria and two ventricles)(14).

The heart valves regulate the blood flow between the atria and ventricles(15).

These valves include left atrioventricular (mitral), right atrioventricular (tricuspid), aortic, and pulmonary valves. The right side of the heart handles deoxygenated blood (low in oxygen and high in carbon dioxide). In contrast, the left side pumps oxygenated blood (high in oxygen and low in carbon dioxide). Meanwhile, the lungs occupy the pleural cavities that function as the site of respiration and gas exchange. These bilateral structures consist of lobes and bronchopulmonary segments separated by fissures(16).

Air enters and leaves the lungs through a network of passageways, such as the trachea, bronchi, bronchioles, and alveoli. The parietal (outer) and visceral (inner) pleura are the two layers that surround each lung. The parietal pleura is attached to the chest wall, while the visceral pleura covers the lungs and adjoining structures through bronchi, blood vessels, and nerves(17).

Several structures that enter each lung via the root (hilum) are the principal bronchus, bronchial vessels, two pulmonary veins, pulmonary artery, pulmonary autonomic plexus, lymph nodes and vessels, and connective tissues.

1. Kudzinskas, A., & Callahan, A. L. (2020). Anatomy, Thorax. In StatPearls [Internet]. StatPearls Publishing.
2. Ibid.
3. Ibid.
4. Ibid.
5. Ibid.
6. Ibid.
7. Ibid.
8. Stoddard, N., & Lowery, D. R. (2020). Anatomy, Thorax, Mediastinum. In StatPearls [Internet]. StatPearls Publishing.
9. Ibid.
10. Ibid.
11. Roberts, K. P., & Weinhaus, A. J. (2005). Anatomy of the Thoracic Wall, Pulmonary Cavities, and Mediastinum. In Handbook of Cardiac Anatomy, Physiology, and Devices (pp. 25-50). Humana Press.
12. Ibid.
13. Ibid.
14. Moorman, A., Webb, S., Brown, N. A., Lamers, W., & Anderson, R. H. (2003). Development of the heart: (1) formation of the cardiac chambers and arterial trunks. Heart (British Cardiac Society), 89(7), 806–814. https://doi.org/10.1136/heart.89.7.806
15. Ibid.
16. Roberts, K. P., & Weinhaus, A. J. op. cit.
17. Ibid.