RELATIONSHIPS OF THE
TRACHEA AND MAIN BRONCHI
The trachea begins at the lower border of the
larynx (just below the cricoid cartilage) at about the level of the sixth
cervical vertebra and ends at about the level of the upper border of the fifth
thoracic vertebra, where it divides into the two main bronchi. The thyroid
gland lies on the anterior and both lateral aspects of the highest part of the
trachea.
As the aorta arches over the root of
the left lung, it first lies anterior to the trachea and then on its left side.
The major arteries arising from the aortic arch are in close relationship with
the trachea. The brachiocephalic (innominate) artery at first is anterior to the
trachea and then is on its right side before dividing into the right common
carotid and right subclavian arteries. The left common carotid artery is first
anterior to and then on the left lateral aspect of the trachea.
The left brachiocephalic (innominate)
vein crosses from left to right, anterior to the trachea and partly separated
from it by the major branches of the aortic arch. The right brachiocephalic
vein is separated from the trachea by the right brachiocephalic artery.
The beginning of the right main
bronchus lies ante- rior to the esophagus. As it courses inferiorly and
laterally to divide into the lobar bronchi, it is posterior to the right
pulmonary artery. The bronchus crosses in front of the azygos vein and is separated
from the thoracic duct by the esophagus. The relationship to other structures
at the root of the lung is shown in Plate 1-13. The beginning of the left main
bronchus also lies anterior to the esophagus, from which it runs laterally and
inferiorly to reach the hilum of the left lung. Because its course is less
vertical than that of the right main bronchus (less in a direct line with the
trachea), foreign bodies are a little more likely to enter the right bronchus
than the left.
The left recurrent laryngeal nerve
arises from the left vagus nerve as it crosses the arch of the aorta and swings
posteriorly to loop around the aortic arch just lateral to the ligamentum
arteriosum. This nerve then runs cranially in the groove between the trachea
and the esophagus to reach the larynx.
The esophagus starts as a continuation
of the pharynx at the lower border of the larynx and continues through the
thorax. It then passes through the esophageal aperture of the diaphragm to
enter the abdominal cavity and terminate at the stomach.
The ligamentum arteriosum, the remnant
of the ductus arteriosus, runs from the beginning of the left pulmonary artery
to the undersurface of the arch of the aorta. In fetal life, the ligamentum
arteriosum shunts blood from the pulmonary artery to the aorta, so that fetal
blood does not pass through the pulmonary circulation.
The vagus nerves split into several
bundles below the root of the lung and form the esophageal plexus on the
surface of the esophagus. Other contributions to the plexus come from the
sympathetic trunks and splanchnic nerves. At the lower end of the plexus, two trunks
are formed, which pass through the esophageal aperture of the diaphragm. The
anterior trunk is mostly derived from the left vagus and the posterior trunk mostly
from the right vagus.
Also worthy of note are the pulmonary
veins, shown cut at the roots of the right and left lungs; the parietal pleura,
cut to expose the lungs, each of which is covered by visceral pleura; the cut
edge of the pericardium; and the inferior vena cava passing through the
diaphragm.
