5.1: Introduction to Pulmonology
The main function of the respiratory system is two-fold: (1) to deliver oxygen to the cells
of the body and (2) remove
... [Show More] carbon dioxide from the body. This is accomplished through
the combination of the upper respiratory tract working in communication with the lower
respiratory tract. A diagram of the anatomy of the respiratory tract is shown in Figure 5.1.
The upper respiratory tract(URT) is outside the chest cavity and includes the nose, and
nasopharynx (down to the larynx). The lower respiratory tract(LRT) includes the organs
within the chest including the trachea, bronchial tree, and lungs. When a person breathes
in air, oxygen diffuses across the alveoli (microscopic sacs) in the lungs where it is
exchanged for carbon dioxide. The diffused oxygen is then taken to the rest of the body
through the circulatory system.
Figure 5.1 Anatomy ofthe Respiratory Tract. Above is a diagram of the anatomy of the respiratory tract broken
down between the Upper Respiratory Tract (URT) and the Lower Respiratory Tract (LRT).
There are several common diseases that affect the airways and this exchange of gas, the
most common of which are asthma and chronic obstructive pulmonary disease (COPD).
Asthma is the general term for recurrent and reversible shortness of breath resulting
from the narrowing of the bronchi and bronchioles.
COPD consists of both emphysema and chronic bronchitis.
Emphysema is a disease process involving inflammation of the alveoli.
Chronic Bronchitis is characterized by chronic inflammation or irritation on the lower
respiratory tract, specifically the bronchi.
The primary drugs used in the treatment of both asthma and COPD include
bronchodilators and a variety of anti-inflammatory and antiallergic agents.
Pathophysiology
All three of these diseases have one primary similarity in that they all involve obstruction
of airflow through the airways.
Chemical Mediators are defined as a substance released from mast cells and white blood
cells during inflammation and allergic reactions. As such, chemical mediators are
responsible for most of the symptoms and complications associated with asthma and
COPD. The only chemical mediator with a known involvement where drug therapy has
been shown to help patient symptoms is leukotrienes. Leukotrienes are potent
bronchoconstrictors with a long duration of action. They stimulate receptors responsible
for bronchoconstriction, edema and other inflammatory actions. There is a class of drugs
called leukotriene inhibitors that inhibit these actions and have an important role in
treating asthma specifically.
Asthma
The narrowing of the bronchioles can be caused by bronchospasm, inflammation, edema
and the production of mucus. This ultimately obstructs airflow meaning that the carbon
dioxide cannot get out and the oxygen cannot get in.
There are different types of asthma. Some asthma is caused by outside factors such as
allergens; this is often referred to as allergic asthma. Conversely, intrinsic asthma is
caused by unknown factors. In some cases, certain factors have precipitated the asthma
attack such as respiratory infections, stress, or cold weather. It is not fully understood why
some people seem to be predisposed to asthma attacks.
Emphysema
Emphysema occurs when the air spaces within the bronchioles enlarge as a result of the
destruction of the alveolar walls. As the alveolar walls are destroyed, there is less surface
area available for oxygen and carbon dioxide exchange. The cause of this appears to be
enzymes that are released in response to inflammation. These enzymes are increased by
air pollution, tobacco smoke, and other irritants to the respiratory tract. Hyperinflation is
the result of the air spaces being enlarged. These patients have difficulty expelling air from
the lungs. This results in a reduction in gas exchange and the feeling of shortness of
breath. Emphysema causes irreversible lung damage over time. [Show Less]