In medical terminology, the chest (or the thorax) comprises of a bony-cage which contains the two lungs, the heart along with the other structures in the mediastinum, which is the space between the two lungs.
The bony-cage is the major part of the chest-wall. It includes twelve ribs on each side attached to the sternum (i.e. the breast-bone) in the front and to the spine (the vertebrae) at the back. Inferiorly, the chest is separated from the abdomen by the two diaphragms, while superiorly, the thoracic cage is bound by the first rib and the clavicle on each side. The thoracic cage is supported by a number of inter-costal and vertebral muscles. The inside of the chest wall is lined by a smooth membrane – the parietal pleurae. Similarly, the lungs on the outside are lined by visceral pleurae. The parietal and visceral pleurae together form a potential space between them i.e. the pleurae cavity.
The mediastinum is the central part of thorax between the two lungs on each side. Mediastinum is continuous with the structures in the neck above and with the abdominal structures below through different openings. Mediastinum contains the heart along with the major vessels (aorta and main pulmonary arteries), esophagus (food pipe), several nerves, lymphatics and lymph nodes.
The lungs have the following important components:
- Tracheo-bronchial tree: The air tubes which conduct air (from outside atmosphere) through the nose and the mouth to the interior of the lungs – the alveoli.
- Alveoli: These are the tiny, bubble like structures which contain the air and constitute the main gas-exchange areas in the lungs.
- Lung interstitium: This consists of spaces between the alveoli, contains pulmonary capillaries, nerves, lymphatics, collagen and loose areolar tissues,.
Involvement in diseases
Different diseases are known to involve different parts of lungs or the respiratory system. There however is no strict compartmentalization. A disease which starts in one part can also involve the other part. Based on the principal site of involvement, the diseases are broadly classified as follows:
- Diseases of trachea-bronchial tree – asthma, chronic bronchitis, tracheitis and laryngitis, chronic obstructive lung disease, bronchiectasis, bronchiolitis, tumours.
- Alveolar diseases: Pneumonias, alveolar proteinosis, tuberculosis
- Interstitial diseases: Interstitial lung diseases e.g. pulmonary fibrosis, sarcoidosis, hypersensitive pneumonia, tuberculosis and others
- Pleural diseases: Pleural effusions, pneumothorax, emphysemas; pleural tumours.
- Mediastinal diseases: Tumours, sarcoidosis, tuberculosis
- Pulmonary vascular diseases – Pulmonary hypertension; vasculitis
- Diseases of respiratory control system: Sleep apnoea syndrome and other ventilator control diseases.
The classification given above is meant to give a broad, general idea. A host of systemic diseases as well as the diseases of other organs (e.g. cardiac, renal or neurological diseases) can also involve the lungs. Moreover, the list of diseases is not complete.
There are many other diseases which may be relatively uncommon, but not unknown. Each disease and each patient have different characteristics which need to be kept in mind.
