Biomedical Engineering Reference
In-Depth Information
FIGURE 9.1
Anatomical arrangement of the
components of the respiratory system. Air enters
from either the nose (nasal cavity) or the mouth
and passes into the pharynx. From here, air
passes through the larynx, the trachea, and the
primary bronchi. The bronchioles continually
divide until the air reaches the alveoli where gas
is exchanged with the cardiovascular system.
Only the conducting portion of the respiratory
system is shown in this figure.
Nasal cavity
Pharynx
Upper respiratory system
Larynx
Trachea
Bronchus
Lower respiratory system
Esophagus
Bronchioles
Right
lung
Left
lung
passes through the upper portion of the respiratory system, which is composed of various
passageways that deliver air to the lungs. The initial conduits for air to flow are typically
the nose, the nasal cavity, the mouth, the pharynx, the larynx, and the trachea (
Figure 9.1
).
All of these passageways, with the exception of the mouth, are lined with a mucous mem-
brane, which act as a first-line defense against toxins or particulate matter within the air.
The mucous membrane traps toxins and particulate matter and brings them into close
proximity with white blood cells for removal and/or destruction. The other major function
of these conducting passages is to warm atmospheric air to body temperature and to
humidify atmospheric air to body conditions. Under very dry conditions, it is common for
the nasal cavity to lose its moisture and then the blood capillaries in the nose rupture,
causing a nosebleed, because all of the moisture has been used to humidify the atmo-
spheric air.
The respiratory system is composed of many branching conducting pathways, to effec-
tively transport and deliver the air into a close proximity with the cardiovascular system.
This branching pathway also increases the available surface area for gas exchange. The
branching respiratory passageways begin with the trachea, which branches into the right
and left bronchi (
Figure 9.2
). Each bronchi divides into smaller secondary bronchi, which
branches into smaller tertiary bronchi. These tertiary bronchi divide approximately three
to five times into smaller bronchi within the lungs. Eventually, the bronchi give rise to
bronchioles, which themselves divide approximately five times, eventually branching into
the terminal bronchioles. Terminal bronchioles have an internal diameter in the range of
500
m and there are approximately 6000 terminal bronchioles that arise from each tertiary
bronchi (there are approximately 20 tertiary bronchioles in the lungs). This branching
structure is very similar to the arterial vascular branching pattern between the single large
aorta and the many terminal arterioles.
The larger conducting pathways within the lungs are surrounded by cartilage. Cartilage
is relatively stiff and acts to protect the airways from collapsing or over-expanding during
μ
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