Smoker's Lung
Pathology Photo Essay
Medical Author: Michael C. Fishbein, M.D.
Medical Revising Editor: Jay W. Marks, MD
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.
Table of Contents
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.
Figure 1: NORMAL 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.
Figure 2: 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.
Figure 3: 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.)
Next: What processes determine normal function of the lung? »
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