DISCUSSION: What are some similarities and differences between chronic bronchitis and emphysema in terms of anatomical/cellular, chemical, and functional changes?
Chronic bronchitis and emphysema are both chronic obstructive pulmonary diseases. Both are due to serious structural changes in the lungs. Both affect proper gas exchange and the ability to breathe comfortably.
COPD is defined as “a preventable and treatable disease with some significant extrapulmonary effects that may contribute to the severity in individual patients.” In chronic obstructive pulmonary diseases, the lungs undergo pathological changes to their structure. Such diseases are thought to be due to causes such as smoking, exposure to toxic chemicals, air pollution, and as a consequence of a previous severe lung infection.
Chronic bronchitis is hypersecretion of mucus with a chronic productive cough that lasts for at least three months of the year for at least two consecutive years. Inspired irritants increase mucus production, and the size and number of mucous glands and goblet cells increase as well. The mucus is thicker and more tenacious than normal mucus. This makes it difficult to clear the mucus from the lungs. As ciliary function is impaired in this condition, clearance is further impaired. This increases the sufferer’s susceptibility to pulmonary infections.
Such infections may further increase mucus production. Eventually the bronchial walls will become thickened from edema and build-up of inflammatory cells. As this vicious cycle repeats, there will eventually be permanent narrowing of the airways. Airway obstruction leads to decreased alveolar ventilation and hypercapnia, or increased PaCO2. When PaCO2 rises, pH drops, leading to respiratory acidosis. Hypoxemia may accompany respiratory acidosis. Prolonged hypoxemia leads to complications such as cyanosis, erythemia, asterixis, myoclonus, and seizures.
Emphysema is an abnormal permanent enlargement of the acini accompanied by destruction of alveolar walls. This destruction is caused by an imbalance between proteases and antiproteases. The excess proteases break down the elastin within the septa of the alveoli. The loss of elastic recoil in the structures of the airway disrupts proper gas exchange, resulting in hypoxemia.
Emphysema is classified as either primary or secondary. Primary emphysema is the result of an inherited deficiency of a1-antitrypsin. Secondary emphysema is caused by injury to lungs due to inhalation of toxins. Smoking is often implicated in the development of emphysema.
Emphysema can be further classified as centriacinar (centrilobular) or panacinar (panlobular.) These classifications are given depending on the area of the lung affected. Septal destruction in centriacinar pneumonia occurs mostly in the upper lobes of the lung, in the respiratory bronchioles and alveolar ducts. In this type of emphysema, the alveolar sacs distal to the respiratory bronchiole remain intact. Centriacinar emphysema tends to occur in conjunction with chronic bronchitis. It tends to occur primarily in secondary emphysema.
Panacinar emphysema affects the entire acinus. It affects the lower lobes of the lung. This type of emphysema tends to affect the elderly. It also usually occurs in primary emphysema.
DISCUSSION: Include an explanation of alveolar remodeling and its consequences to efficient ventilation and external respiration.
In normal alveologenisis, the cells of the alveoli are of optimal shape for proper gas exchange. But when there is damage to the cells, they do not reform properly. They may become stretched too thin, or they may become tough and fibrous. This leads to reduction in gas-exchange surface area. With loss of alveolar gas-exchanging units and the capillary bed within them, blood oxygen levels fall and pulmonary circulatory pressure rises. When proper gas exchange is disrupted, proper pH balance is disrupted as well.
Properly functioning alveoli are imperative to oxygen uptake and carbon dioxide elimination. This exchange maintains gradients of soluble gas between blood and tissue cells. These gradients are vital to sustaining cellular metabolism. The lungs are composed of conducting airways, which connect them to the outside environment, and the parenchyma, where virtually all gas exchange occurs.
Physiological pH is maintained through the buffering of hydrogen ions (H+) with bicarbonate ions (HCO3–). These combine to form dissolved carbon dioxide in blood, which equilibrates through diffusion with alveolar gas in the lung and is then eliminated during exhalation. When the structure of the alveoli has been altered, the proper elimination of carbon dioxide is disrupted, resulting in hypoxia.
Recent Comments