3-24. THE TRACHEA
a. The trachea, or windpipe, is a somewhat rigid, noncollapsible, pipe-like tube
about 11 centimeters long. It is situated anterior to the esophagus and extends from the
level of the sixth cervical vertebra to the inferior border of the fifth thoracic vertebra
where it divides into the two bronchi. It extends into the thoracic cavity along the
b. The trachea consists of 16 to 20 C-shaped cartilages, superimposed one
upon the other, forming the anterior two-thirds of the tracheal wall. Posteriorly, these
open along the surface in contact with the esophagus. Consequently, the posterior
surface of the trachea can be forced inward to some extent to allow swallowing of
particles larger in diameter than the esophageal lumen.
3-25. THE BRONCHI
The two bronchi differ slightly. The right bronchus is about one inch in length and
the left bronchus about two inches. Each bronchus enters its corresponding lung at a
depression on the mediastinal surface, known as the hilus of the lung. As the bronchus
extends into the lung, it divides and subdivides into smaller branches (bronchioles).
Tiny air sacs, the alveoli, are at the terminal ends of the bronchioles.
3-26. THE LUNGS
a. The two lungs, one on either side within the thoracic cavity, are the essential
organs of respiration. They are separated by the heart and mediastinal structures.
Each lung is conical in shape, conforming generally to the shape of the cavity within
which it lies. The broad base rests upon the diaphragm while the apex extends about
one inch above the clavicle into the root of the neck.
b. Deep fissures into lobes divide each lung. The right lung has three lobes and
the left lung two. The substance of the lungs is light, porous, and spongy owing to its
numerous air-containing elements. The alveoli have very thin walls, and are
surrounded by a network of capillary blood vessels. It is here that the interchange of
3-27. THE PLEURA AND THE PLEURAL CAVITY
a. Each lung is invested with a serous membrane, the pulmonary or visceral
pleura. The rest of the membrane is called the parietal pleura. Different portions of the
parietal pleura are called by special names that indicate their position. From the medial
surface of each lung, the parietal pleura are reflected over the root (formed by the
bronchus, nerves, and vessels) to the posterior surface of the sternum anteriorly and to
the vertebral column posteriorly forming the mediastinal pleura. That portion lining the
inner surface of the walls formed by the ribs is the costal pleura and that covering the
top of the diaphragm is the diaphragmatic pleura.