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What Is the Thorax?
The thorax, also known as the chest, is a region found between the abdomen and neck region of mammals, tetrapods and humans. Thorax in humans is composed of the thoracic wall and thoracic cavity that houses different organs such as the heart, thymus gland, lungs, muscles and other internal structures.
On the lower side of the thorax is the diaphragm. The bones in the human thorax consist of the breastbone, 12 thoracic vertebrae and 12 pairs of ribs.
Structure and Anatomy
Thoracic Wall
The thoracic wall of the thorax is formed by the breastbone (sternum), cartilage, 12 pairs of ribs, 12 thoracic vertebrae and five muscles. The thoracic wall functions to help in movement, respiration and keeping the thoracic cavity safe.
The posterior thoracic wall is made up of the vertebrae and intervertebral discs. Each rib joins with two vertebral bodies and curves inferiorly, posteriorly and laterally. The true ribs articulate with the breastbone anteriorly; the false ribs have cartilaginous extensions to articulate with the sternum, while the floating ribs do not communicate with the sternum at all.
The five muscles of the thoracic wall, from deep to superficial, are transversus thoracis muscle, subcostalis, innermost intercostal, internal intercostal and external intercostal. These muscles help in respiration by expanding and contracting the thoracic cavity. They also help in the movement of the spine, girdle and pelvis.
The anterior thoracic wall is made up of breast tissue that is composed of mammary glands, nipples, fat, fibrous tissue and areolar complex.
Thoracic Cavity
The thoracic cavity is deep-seated within the thoracic walls; it lies superiorly to the diaphragm and inferiorly to the neck. This cavity houses many important organs, such as lungs, bronchi, pleura and trachea that take part in respiration; great vessels, pericardium, heart and lymphatics that take part in cardiovascular activities; vagus nerve, sympathetic chain, phrenic nerve, and recurrent laryngeal nerve that form a part of the nervous system; the thymus gland of the immune system and the oesophagus of the digestive system.
The thoracic cavity is divisible into two visible compartments, namely the mediastinum and the pleural cavity. The pleural cavities are found in pairs containing the left and right lung and the pleura. The mediastinum is located centrally, with the pleural cavities on the sides. The mediastinum arises from the inner border of the sternum in the front, and from the vertebral bodies in the back and runs through the whole length of the thoracic cavity.
A thoracic plan runs at a horizontal angle to the sternum via T4-T5 and divides the mediastinum into the superior and inferior mediastinum.
Clinical Significance
Injury or trauma to the chest can lead to the following conditions:
- Injury: Chest trauma, thoracic injury or thoracic trauma can cause death in 25% of the cases. It is caused due to obstructed blood or airflow, oesophageal perforations, or leakage in the alimentary tract. Fractures, compromised ventilation and direct lung injuries can also cause chest trauma.
- Pain: Chest pain can be related to a number of problems such as musculoskeletal, digestive or respiratory problems. While not all chest pain is related to cardiac issues, it should not be ignored. Symptoms of cardiac chest pain include pressure in the chest and intense pain in the back, arms and neck.
Pain due to non-cardiac reasons gives a burning sensation in the digestive and respiratory tract. Chest pain is also associated with a heart attack, which gives extreme discomfort in the chest, equivalent to a heavy weight placed on the body.
- Atelectasis: It is a non-cardiac chest pain that is caused when a small portion of the lung collapses due to the absence of air. In this condition, the bronchial tubes are blocked, and the person faces shortness of breath. This blockage is caused due to the presence of a tumour, mucus plug or foreign object in the bronchi.
- Pneumothorax: It is a condition in which the pleural space is filled up with air or gas. It can occur due to lung injury or lung disease. The size of the pneumothorax can increase if not operated upon. However, smaller cases tend to resolve by themselves.
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