agents from reaching the air sacs. However, this can also lead to respiratory
distress.
A very important feature of the trachea is the action of cilia, hair-like
structures that beat rhythmically back and forth in the air passage (Figure
7.1a). With a speed of 1300 beats per minute, billions of cilia function like a
broom to sweep noxious foreign agents out of the system.
The condition commonly called bronchitis is caused by infection of the air
passages, starting at the nose and extending through the bronchioles. Acute
bronchitis may result from inhaled irritants, such as smoke, dust, and
chemicals. It can also be due to allergy. Chronic bronchitis usually develops
slowly and appears in people past the midway point of their lives. It occurs
approximately four times more often in men than in women, and more often
among city dwellers than rural residents. The most significant symptom is
cough, which may be constant or intermittent. Mucus is almost always
coughed up, which may be clear or may contain pus or streaks of blood. In
many cases, because the patient is not severely ill or incapacitated, medical help
is not sought, and so the cough and expectoration persist.
7.2.1.3 Alveoli
There are about 400 million alveoli in the lungs of a healthy adult. The inner
surfaces of the alveoli, continuous with the bronchioles, bronchi, and trachea,
are technically outside the body as they are in contact with the atmosphere. If
the walls of all the air cells were spread out as one continuous area, they would
cover a surface the size of a tennis court. Because this immense surface is
compacted into the small space of two lungs, the walls of the air cells are
extremely thin. This is essential to allow absorption of O 2 from air and
dispersal of CO 2 waste gases to take place (Figure 7.1b). Particulate matter that
reaches the alveoli and is deposited is usually 1mm or less in diameter.
Particulates with a diameter less than 0.5 mm are small enough to behave like
gases.
There are four types of cells in the alveoli: alveolar epithelial cells,
endothelial cells, large alveolar cells, and alveolar macrophages. Alveolar
epithelial cells are responsible for the exchange of CO 2 and O 2 ; alveolar
endothelial cells are endowed with various protective properties; and large
alveolar cells and alveolar macrophages carry out oxidative and synthetic
processes that defend the lungs against invading organic and inorganic
materials.
Macrophages play a well-known phagocytic role in the lungs and other
tissues. They engulf an organism or a particle by membrane invagination and
pouch formation, and are one of the most important components of the
immune response. A number of environmental agents, such as silica, asbestos,
cigarette smoke, carbon monoxide (CO), sulfur dioxide (SO 2 ), nitrogen dioxide
(NO 2 ), formaldehyde, and aflatoxin and other mycotoxins, can either depress
or enhance the phagocytic function of macrophages.
Defense Responses to Toxicants
101
[16:53 26/8/04 P:/CRC PRESS/4365 MING-HO.751 (1670)/4365-007.3d]
Ref: 4365 MING-HO YU Chap-007 Page: 101 99-110
distress.
A very important feature of the trachea is the action of cilia, hair-like
structures that beat rhythmically back and forth in the air passage (Figure
7.1a). With a speed of 1300 beats per minute, billions of cilia function like a
broom to sweep noxious foreign agents out of the system.
The condition commonly called bronchitis is caused by infection of the air
passages, starting at the nose and extending through the bronchioles. Acute
bronchitis may result from inhaled irritants, such as smoke, dust, and
chemicals. It can also be due to allergy. Chronic bronchitis usually develops
slowly and appears in people past the midway point of their lives. It occurs
approximately four times more often in men than in women, and more often
among city dwellers than rural residents. The most significant symptom is
cough, which may be constant or intermittent. Mucus is almost always
coughed up, which may be clear or may contain pus or streaks of blood. In
many cases, because the patient is not severely ill or incapacitated, medical help
is not sought, and so the cough and expectoration persist.
7.2.1.3 Alveoli
There are about 400 million alveoli in the lungs of a healthy adult. The inner
surfaces of the alveoli, continuous with the bronchioles, bronchi, and trachea,
are technically outside the body as they are in contact with the atmosphere. If
the walls of all the air cells were spread out as one continuous area, they would
cover a surface the size of a tennis court. Because this immense surface is
compacted into the small space of two lungs, the walls of the air cells are
extremely thin. This is essential to allow absorption of O 2 from air and
dispersal of CO 2 waste gases to take place (Figure 7.1b). Particulate matter that
reaches the alveoli and is deposited is usually 1mm or less in diameter.
Particulates with a diameter less than 0.5 mm are small enough to behave like
gases.
There are four types of cells in the alveoli: alveolar epithelial cells,
endothelial cells, large alveolar cells, and alveolar macrophages. Alveolar
epithelial cells are responsible for the exchange of CO 2 and O 2 ; alveolar
endothelial cells are endowed with various protective properties; and large
alveolar cells and alveolar macrophages carry out oxidative and synthetic
processes that defend the lungs against invading organic and inorganic
materials.
Macrophages play a well-known phagocytic role in the lungs and other
tissues. They engulf an organism or a particle by membrane invagination and
pouch formation, and are one of the most important components of the
immune response. A number of environmental agents, such as silica, asbestos,
cigarette smoke, carbon monoxide (CO), sulfur dioxide (SO 2 ), nitrogen dioxide
(NO 2 ), formaldehyde, and aflatoxin and other mycotoxins, can either depress
or enhance the phagocytic function of macrophages.
Defense Responses to Toxicants
101
[16:53 26/8/04 P:/CRC PRESS/4365 MING-HO.751 (1670)/4365-007.3d]
Ref: 4365 MING-HO YU Chap-007 Page: 101 99-110