Page 879 - Fundamentals of anatomy physiology

866 Unit 5 Environmental Exchange Esophagus
Figure 23–6 The Anatomy of the Trachea. ATLAS: Plates 42b,c

Hyoid
bone

Larynx

Trachealis
muscle

Lumen of Thyroid
trachea gland

Trachea Respiratory
epithelium
Root of
right lung Tracheal Tracheal
cartilages cartilage
Lung
tissue Location of carina The trachea LM × 3
(internal ridge) b A cross-sectional view
RIGHT LUNG
Primary Root of diameter of the trachea. This narrowing increases the tube’s re-
bronchi left lung sistance to airflow. The normal diameter of the trachea changes
Secondary from moment to moment, primarily under the control of the
LEFT LUNG sympathetic division of the ANS. Sympathetic stimulation in-
bronchi creases the diameter of the trachea and makes it easier to move
large volumes of air along the respiratory passageways.

a A diagrammatic anterior view showing the plane of section The Primary Bronchi
for part (b)
The trachea branches within the mediastinum into the right
23 The epithelium of the trachea is continuous with that of and left primary bronchi (BRONG-kı.; singular, bronchus). An
the larynx. The mucosa of the trachea resembles that of the internal ridge called the carina (ka-RI.-nuh) separates the two
nasal cavity and nasopharynx (Figure 23–2a). The submucosa bronchi (Figure 23–6a). Like the trachea, the primary bronchi
(sub-mu. -KO. -suh), a thick layer of connective tissue, surrounds have C-shaped rings, but the ends of the C overlap. The right
the mucosa. The submucosa contains mucous glands that com- primary bronchus supplies the right lung, and the left supplies
municate with the epithelial surface through a number of se- the left lung. The right primary bronchus is larger in diameter
cretory ducts. The trachea contains 15–20 tracheal cartilages, than the left, and descends toward the lung at a steeper angle.
which serve to stiffen the tracheal walls and protect the airway For these reasons, most foreign objects that enter the trachea
(Figure 23–6a). They also prevent it from collapsing or overex- find their way into the right bronchus rather than the left.
panding as pressures change in the respiratory system.
Before branching further, each primary bronchus travels
Each tracheal cartilage is C-shaped. The closed portion of to a groove along the medial surface of its lung. This groove,
the C protects the anterior and lateral surfaces of the trachea. The the hilum of the lung, also provides access for entry to pulmo-
open portion of the C faces posteriorly, toward the esophagus nary vessels, nerves, and lymphatics (Figure 23–7c). The entire
(Figure 23–6b). Because these cartilages are not continuous, array is firmly anchored in a meshwork of dense connective
the posterior tracheal wall can easily distort when you swallow, tissue. This complex is the root of the lung (Figure 23–6a).
allowing large masses of food to pass through the esophagus. The root attaches to the mediastinum and fixes the positions
of the major nerves, blood vessels, and ­lymphatic vessels.
An elastic ligament and the trachealis muscle, a band The roots of the lungs are anterior to v­ ertebrae T5 (right) and
of smooth muscle, connect the ends of each tracheal cartilage T6 (left).
(Figure 23–6b). Contraction of the trachealis muscle reduces the