Introduction to the Thorax

The thorax, commonly known as the chest, is the upper portion of the trunk extending from the neck to the diaphragm. It is a complex region that not only houses vital organs like the heart and lungs but also provides a protective framework thanks to its bony and muscular structures. The thorax is defined superiorly by the thoracic inlet (or superior thoracic aperture) and inferiorly by the diaphragm, which plays a crucial role in respiration .

The Thoracic Wall

The thoracic wall forms a sturdy yet flexible cage that protects the internal organs. Its main components include:

• Bony Skeleton:

  • Sternum: The flat bone in the midline of the chest that serves as an attachment point for several muscles.

  • Ribs: Twelve pairs of ribs curve around the thorax, attached posteriorly to the thoracic vertebrae and anteriorly to the sternum (either directly or via costal cartilages).

  • Thoracic Vertebrae: Twelve vertebrae that form the posterior boundary of the thoracic cage.

• Joints and Spaces:

  • Intercostal Spaces: These are the gaps between adjacent ribs that contain intercostal muscles, veins, arteries, and nerves, each playing a role in both protection and the mechanics of breathing.

  • Joints: Connective interfaces include costovertebral joints, sternocostal joints, and costochondral joints that allow the rib cage to move during respiration .

• Musculature:

  • Layers of intercostal muscles (external, internal, and innermost) facilitate the expansion and contraction of the rib cage.

  • Additional muscles such as the transversus thoracis, subcostal muscles, and accessory muscles (e.g., serratus posterior) contribute to the thoracic wall’s motion and stability.

The Thoracic Cavity

Inside the thorax lies the thoracic cavity, which itself can be divided into distinct compartments:

• Mediastinum:

  • This central compartment is bordered laterally by the pleural cavities. It is further subdivided into superior and inferior regions (with the inferior mediastinum often split into anterior, middle, and posterior compartments).

  • Within the mediastinum reside key structures such as the heart, the roots of the great vessels, the trachea, the esophagus, and the thymus. The heart is encased in the pericardium for additional protection.

• Pleural Cavities:

  • Flanking the mediastinum on each side, these cavities house the lungs. Each lung is enveloped by a double-layered pleural membrane that produces lubricating fluid for smooth respiratory movements.

  • Notably, the lung anatomy is characterized by lobes: the right lung typically has three lobes, while the left lung has two, accommodating the position of the heart .

Neurovascular Structures and Their Significance

The thorax is traversed by major neurovascular bundles that are essential for supplying blood and innervation to both the chest wall and the internal organs:

• Arterial Supply:

  • The aorta, which arches and descends through the thorax, gives off several key branches, including the brachiocephalic trunk, left common carotid, and left subclavian arteries.

  • Additional arteries, such as the internal thoracic arteries, further supply the chest wall.

• Venous Drainage:

  • Major veins such as the superior vena cava (SVC) and azygos venous system collect deoxygenated blood from the thoracic structures and return it to the heart.

• Nervous Innervation:

  • The intercostal nerves, which arise from the thoracic spinal nerves, ensure the sensory and motor innervation of the thoracic wall.

  • Moreover, important autonomic plexuses in the thorax help regulate functions of the heart, lungs, and other organs .