Smoker's lung introduction
Picture of normal airway and lung
Cigarette smoking is associated with a wide variety of abnormalities throughout the body that cause not only illness, but also, all too often, death. Indeed, if all deaths from diseases related to smoking (lung disease, heart disease, and cancers of many different organs) were considered, a case could be made for cigarette smoking as the leading cause of death in industrialized countries. Ironically, it is also the most preventable cause of death in our society!
This photo essay will focus on smoker's lung. The term "smoker's lung" refers to the structural and functional abnormalities (diseases) in the lung caused by cigarette smoking. First, the normal structure and function of the lung will be described and illustrated. Then, the structural and functional abnormalities caused by smoking will be described and illustrated.
What is the structure of the normal lung?
We have a right lung and a left lung that reside in the chest cavity and surround the heart. A thin membrane called the pleura covers the outer surface of the lung. The air we breathe gets into the lung through an airway (path for air). Figure 1 is a diagram showing the main parts of the airway and lung.
The airway consists of the oral and nasal cavities, which connect to the voice box (larynx), which connects to the windpipe (trachea). Note in the diagram that the windpipe splits into two air passages called bronchi, one going to each lung (right and left main bronchi). The trachea and larger bronchi contain C-shaped rigid bars of cartilage in their walls. The cartilage helps to keep the airway from collapsing when there is negative pressure in the airway, as occurs when we breathe in (inhale or inspire). The right lung has three separate sections (upper, middle, and lower lobes), while the left lung has just an upper and a lower lobe. Each lobe has its own bronchi and blood supply.
Further along in the airway, within the lung, the bronchi continue to divide into ever-smaller (narrower) tubes, much like the branches of a tree. (Hence, the term tracheobronchial tree.) The walls of the bronchi contain muscles that can cause the airway to expand (widen) or contract (narrow). For example, during exercise, the airway expands to increase airflow (ventilation). Conversely, when exposed to polluted or very cold air, the airway contracts to protect the downstream tissues from injury. The smaller branches of the bronchial tree, called bronchioles, also contain muscle, but they lack cartilage. Notice in Figure 1 that the very smallest bronchioles (respiratory bronchioles) connect directly to tiny air sacs in the lung, called alveoli. Figure 2 shows a microscopic section of a normal bronchial wall.
Picture of normal bronchial wall
In this picture, you can see that the bronchial wall contains cartilage and muscle, as described above. Also, note that different types of cells make up the lining (epithelium) of the bronchi (as well as of the trachea and bronchioles). One type of cell is called a goblet cell because of its shape. The goblet cells produce mucus, which lubricates the airways and traps inhaled foreign material (e.g., bacteria, viruses, and pollutants). Other cells in the epithelium are called ciliated cells, which are discussed in the next paragraph. Beneath the surface of the airway, the goblet cells and other epithelial cells are clustered into structures called bronchial glands. These glands secrete additional mucus and other lubricating fluids.
Inflammatory cells are also in the normal bronchial wall. Look again at Figure 2 and observe that they are scattered beneath the lining of the airway. These inflammatory cells, also known as white blood cells, include neutrophils, lymphocytes, and macrophages. Their job (in this situation) is to destroy and/or engulf any inhaled foreign material that becomes trapped in the mucus. In doing so, however, inflammatory cells create debris. To help dispose of the debris, most of the cells that line the airway have hair-like processes called cilia. These ciliated cells sweep and push the foreign material and debris up into the larger airways where they can be coughed up or spit out.
The lung resembles a sponge and is composed of millions of alveoli. This structure provides a huge surface for gas exchange that has been estimated to be equal to the size of a tennis court. (These tiny air sacs can be seen with a magnifying glass.) Figure 3 is a microscopic section of a normal lung, showing the alveoli.
Picture of normal lung alveoli
The wall (alveolar septum) of each alveolus contains a very small blood vessel called a capillary. Blood flows slowly through each capillary to allow time for the lung to perform its main function, which is the exchange of gas (oxygen and carbon dioxide). The actual site for gas exchange is pictured in the high magnification section on the right side of figure 3. Thus, the capillary blood picks up oxygen (O2) from the inhaled air in the alveoli. At the same time, the capillary blood releases the body's waste gases, most importantly carbon dioxide (CO2), into the alveoli. (Waste gases are by-products of the body's metabolism.)