Lungs play a critically important role by extracting oxygen from the air inhaled, which is then distributed via the bloodstream to every cell in the body. At the same time, when a cell uses oxygen, it produces waste - carbon dioxide - that is expelled by the lungs during each exhalation.
The major components of the respiratory system are the bronchi, the larger conducting airways that begin at the end of the trachea and go into the lung; the bronchioles, the more narrow airways that branch from the bronchi; and alveoli, tiny air sacs located at the end of the bronchioles where the exchange of oxygen and carbon dioxide takes place -- the respiratory zone. Blood carries oxygen from the respiratory zone to cells and returns carbon dioxide to the respiratory zone for disposal via exhalation.
When lungs become diseased, they no longer can maintain the necessary exchange of oxygen and carbon dioxide. A number of diseases and conditions can cause lungs to become so dysfunctional that one or both of them may need to be replaced through transplantation. These can include:
- Chronic Obstructive Pulmonary Disease (COPD) - This disease, which mainly includes chronic bronchitis and emphysema, involves obstruction of airflow through the airways and out of the lungs and it is usually permanent and progressive.
- Pulmonary Fibrosis or Interstitial Lung Disease (ILD) - ILD is a general term that includes many chronic lung disorders in which the lung is damaged, the walls of the air sacs become inflamed and then scarring (i.e., pulmonary fibrosis) begins in the tissue between the air sacs (interstitium). This causes the lungs to become stiff and smaller in volume.
- Cystic Fibrosis - This genetic disease is characterized by the production of abnormal secretions and damage to airways, leading to mucus build-up that impairs respiration when it occurs in the lungs.
- Bronchiectasis - In this disorder, the airways become enlarged and distended, forming pockets where infection can develop. This alters the lining of the airways, damaging the lung's cleaning system and causing dust, mucus and bacteria to accumulate and infection to occur.
- Pulmonary Hypertension - A disorder in which the pressure in the pulmonary circulation is above normal levels. This rare disorder can cause permanent damage to the lungs and become life-threatening. When there is no known cause, it is called primary pulmonary hypertension. Pulmonary hypertension that occurs as a result of other disorders is called secondary pulmonary hypertension. Pulmonary hypertension caused by an abnormal development and defects in the heart and great vessels is called Eisenmenger's syndrome.
- Sarcoidosis - A systemic disease in which chronic inflammation causes granulomas (small lumps) to develop in body tissues - often in the lungs, which may lead to scarring.
- Lymphangioleiomyomatosis - This rare disease is characterized by a proliferation of muscle cells that cause the airways, blood and lymph vessels to become obstructed.