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ANATOMY & PHYSIOLOGY

ANATOMY OF THE CHEST WALL & PLEURA

The physiology of respiration and the anatomy of the chest wall are intricately connected. The chest wall is an airtight, expandable, cone-shaped cage comprised of a vast array of skin, fat, muscle, bone, and vital organs. This design serves to facilitate protection of the vital organs as well as ventilation and gas exchange. Normal ventilation occurs when expansion of the rib cage and simultaneous diaphragmatic excursion create negative intrathoracic pressure, allowing inward flow of air.

The function of the chest wall is made possible by its segmentally arranged anatomy. The ventral wall of the bony thorax extends from the suprasternal notch to the xiphoid, approximately 18 cm in the adult. It is formed by the manubrium, sternum, and xiphoid process. The remainder of the anterior wall and the lateral walls are formed by 12 ribs. The first seven pairs of ribs articulate directly with the sternum, the next three pairs connect to the lower border of the preceding rib, and the last two terminate in the wall of the abdomen. The sides of the chest wall consist of the upper 10 ribs, which slope obliquely downward from their posterior attachments. The posterior chest wall is formed by the 12 thoracic vertebrae, their transverse processes, and the 12 ribs (Figure 19–1). The upper ventral portion of the thoracic cage is covered by the clavicle and the subclavian vessels. Laterally, it is covered by the shoulder girdle and axillary nerves and vessels; dorsally, it is covered in part by the scapula.

Figure 19–1.

The thorax, showing rib cage, pleura, and lung fields.

The superior aperture of the thorax (also called the thoracic inlet or the thoracic outlet) is a downwardly slanted 5- to 10-cm kidney-shaped opening bounded by the first costal cartilages and ribs laterally, the manubrium anteriorly, and the body of the first thoracic vertebra posteriorly. The inferior aperture is bounded by the 12th vertebra and ribs posteriorly and the cartilages of the 7th to 10th ribs and the xiphisternal joint anteriorly. The diaphragm comprises a large portion of the lower thoracic cavity.

The blood supply and innervation of the chest wall are via the intercostal vessels and nerves (Figures 19–2 and 19–3). The upper thorax also receives vessels and nerves from the cervical and axillary regions. Blood supply to the underside of the sternum arises from bilateral internal thoracic artery branches, which arise from the intercostal vessels laterally.

Figure 19–2.

Transverse section of thorax.

Figure 19–3.

Intercostal muscles, vessels, and nerves.

The entirety of the thoracic cavity is ...

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