The Tracheobronchial Tree
This follows the page describing the basic anatomy
of the lower respiratory tract.
The term "tracheobronchial tree" or "respiratory
tree" refers to the structures of bronchi and bronchioles that
terminate with
the
alveolar
ducts, sacs, and, finally,
alveoli - that are contained within the lungs. These are the structures
through which air passes into the body (usually through
the nose/mouth then the trachea). Therefore these structures are also
referred to as "airways".
This pages includes two diagrams of the airways - the main structure
of the tracheobroncial tree being shown immediately below, and a second
diagram showing the alveoli in further detail further down the page.
Larger
structures
The trachea divides to form the right- and left- primary bronchi
(as shown). Each of these divide into lobar bronchi - which supply
air to each of the lobes of the lung.
The lobar bronchi divide into segmental bronchi - which supply air
to areas of the lung that are called bronchoplumonary
segments.
Bronchopulmonary segments are functionally and anatomically distinct
from each other - which matters because a segment of diseased lung
can be removed surgically without adversely affecting the rest of
the lung.
Areas of tracheobronchial tree furthest from the trachea are collectively
called the "distal respiratory
tree".
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Above:
Anterior View of the Tracheobronchial
Tree
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Distal
Respiratory Tree
(lower airways)
As shown above, the finest (narrowest) of the bronchial air
tubes are called
"terminal bronchioles".
These lead
to "respiratory bronchioles" which are even smaller tubes whose structure
is different from the terminal bronchioles.
Respiratory bronchioles are lined by ciliated cuboidal
epithelium surrounded by smooth muscle. The respiratory bronchioles
are covered
by small "air cells" called alveoli. Alveolar ducts connects
alveoli to the respiratory bronchiole to which they are attached.
Respiratory bronchioles and alveolar ducts occupy very
similar positions on diagrams but are
distinguished physically by the differences between the structure
of their walls and the tissues that line them. E.g. respiratory
bronchioles are lined with simple ciliated cuboidal epithelium and
Clara cells whereas alveolar ducts are lined with flat nonciliated
epithelium. |
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Above: Distal Respiratory Tree (Gas Exchange Region)
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All of the alveoli are covered by fine blood
capillaries as shown in red for the top aleveolar sace (above).
Others are shown without the capillary network for clarity
of illustration of the alveoli.
The area shaded yellow is a cut-away section
to illustrate that the alveoli are not many closed spheres
but,
rather, are
many microscopic blind-ending air pouches.
Each individual alveolus opens into a larger sac (one of many
such alveoli sacs, each having many individual alveoli), that
is connected to its terminal bronchiole via an alveoli
duct. Also note the alveoli-capillary membrane which
seperates the air inside the alveolus from the blood-carrying
capillary on the outside of the alveolus. This is the membrane
through which the gases oxygen and carbon-dioxide are exchanged
during the breathing process (internal respiration). |
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Re-cap: Structure through the airways |
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1. |
Trachea 
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2.
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Bronchus
(Right- or Left- Primary Bronchus) |
3.
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Lobar
Bronchus
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4.
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Segmental
Bronchus
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5.
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Bronchus
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6.
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Bronchiole
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7.
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Terminal
Bronciole
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8.
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Respiratory
Bronchiole
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9.
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Alveolar
Duct
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10.
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Alveolar
Sac / Alveolus
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_
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| Next: Also see the pages about:
External Respiration and Internal
Respiration.
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