CHAPTER 2: THORAX PART II: THE THORACIC CAVITY Flashcards
OBJECTIVES
■■ To understand the general arrangement of the thoracic viscera and their relationship to one another and to the chest wall.
■■ To be able to define what is meant by the term mediastinum and to learn the arrangement of the pleura relative to the lungs. This information is fundamental to the comprehension of the function
and disease of the lungs.
■■ Appreciating that the heart and the lungs are enveloped in
serous membranes that provide a lubricating mechanism for these mobile viscera and being able to distinguish between such terms as thoracic cavity, pleural cavity (pleural space),
pericardial cavity, and costodiaphragmatic recess.
■■ To learn the structure of the heart, including its conducting system and the arrangement of the different chambers and valves, which is basic to understanding the physiologic and pathologic features of the heart.
The critical nature of the
blood supply to the heart and the end arteries and myocardial
infarction
is emphasized.
■■ To understand that the largest blood vessels in the body are located within the thoracic cavity, namely, the aorta, the pulmonary arteries, the venae cavae, and the pulmonary veins.
Trauma to the chest wall can result in disruption of these
vessels, with consequent rapid hemorrhage and death.
Because these vessels are hidden from view within the
thorax, the diagnosis of major blood vessel injury is often
delayed, with disastrous consequences to the
patie
What are the bounderies of the Chest Cavity?
The chest cavity is bounded by the chest wall and below by the diaphragm. It extends upward into the root of the neck about one fingerbreadth above the clavicle on each side (see
Fig. 3.5).
The diaphragm, which is a very thin muscle, is the only structure (apart from the pleura and the peritoneum) that separates the chest from the abdominal viscera.
The
chest cavity can be divided into a median partition, called the mediastinum, and the laterally placed pleurae and lungs (Figs. 3.1, 3.2, and 3.3).
What is the only structure (apart from the pleura and the peritoneum) that separates the chest from the abdominal viscera.
The diaphragm, which is a very thin muscle, is the only structure (apart from the pleura and the peritoneum) that separates the chest from the abdominal viscera.
The chest cavity can be divided into a :
- median partition, called the mediastinum,
- and the laterally placed pleurae andlungs (Figs. 3.1, 3.2, and 3.3).
Describe the mediastinum.
The mediastinum, though thick, is a movable partition that extends superiorly to the thoracic outlet and the root of the neck and inferiorly to the diaphragm.
It extends anteriorly to the sternum and posteriorly to the vertebral column.
The mediatstinum contains the:
It contains the remains of the thymus, the heart and large blood vessels, the trachea and esophagus, the thoracic duct and lymph nodes, the vagus and phrenic nerves, and the sympathetic trunks.
The mediastinum is divided into __________-by an imaginary plane passing from the sternalangle anteriorly to the lower border of the body of the 4th thoracic vertebra posteriorl
superior and inferior mediastina
The inferior mediastinum
is further subdivided into the ___________
- middle mediastinum
- which consists of the pericardium and heart; the anterior mediastinum, which is a space between the pericardium and the sternum
- and the posterior mediastinum,
- which lies between the pericardium and the vertebral column.
For purposes of orientation, it is convenient to remember
that the major mediastinal structures are arranged in
the following order from anterior to posterior
What are the bounderies of the Superior Mediastinum?
Superior Mediastinum
The superior mediastinum is bounded by
- front :manubrium sterni
- behind: first four thoracic vertebrae (see Fig. 3.2).
What are the contents of the Superior Mediastinum?
- (a) Thymus,
- (b) large veins,
- (c) large arteries,
- (d) trachea,
- (e) esophagus and
- thoracic duct, and
- (f) sympathetic trunks
What are the contents of the Inferior Mediastinum?
- (a) Thymus,
- (b) heart within the pericardium with the phrenic nerves on each side
- , (c) esophagus and thoracic duct,
- (d) descending aorta, and
- (e) sympathetic trunks
What are the bounderies of inferior mediastinum?
The inferior mediastinum is bounded in
- front: body of the sternum and
- behind by the lower eight thoracic vertebrae
Deflection of Mediastinum
In the cadaver, the mediastinum, as the result of the hardening effect of the preserving fluids, is an inflexible, fixed structure.
In the living, it is very mobile; the lungs, heart, and large arteries are in rhythmic pulsation, and the esophagus distends as each bolus
of food passes through it.
If air enters the pleural cavity (a condition called pneumothorax), the lung on that side immediately collapses and the mediastinum is displaced to the opposite side.
This condition reveals
itself by the patient’s being breathless and in a state of shock; on examination, the trachea and the heart are found to be displaced
to the opposite side.
Mediastinitis
The structures that make up the mediastinum are embedded in loose connective tissue that is continuous with that of the root of the neck.
Thus, it is possible for a deep infection of the neck
to spread readily into the thorax, producing a mediastinitis.
Penetrating wounds of the chest involving the esophagus may produce a mediastinitis.
In esophageal perforations, air escapes into the connective tissue spaces and ascends beneath the fascia to the root of the neck, producing subcutaneous emphysema
What is subcutaneous emphyema?
In esophageal perforations, air escapes into the connective tissue spaces and ascends beneath the fascia to the root of the neck, producing subcutaneous emphysema
Mediastinal Tumors or Cysts
Mediastinal Tumors or Cysts
Because many vital structures are crowded together withinthe mediastinum, their functions can be interfered with by an enlarging tumor or organ.
A tumor of the left lung can rapidly
spread to involve the mediastinal lymph nodes, which on enlargement may compress the left recurrent laryngeal nerve, producing paralysis of the left vocal fold.
An expanding cyst or
tumor can partially occlude the superior vena cava, causing severe congestion of the veins of the upper part of the body.
Other pressure effects can be seen on the sympathetic trunks, phrenic nerves, and sometimes the trachea, main bronchi, and esophagus
Mediastinoscopy
Mediastinoscopy is a diagnostic procedure whereby specimens of tracheobronchial lymph nodes are obtained without opening the pleural cavities.
A small incision is made in the
midline in the neck just above the suprasternal notch, and the superior mediastinum is explored down to the region of the bifurcation of the trachea.
The procedure can be used to determine
the diagnosis and degree of spread of carcinoma of the bronchus.

FIGURE 3.1 Cross section of the thorax at the level of the eighth thoracic vertebra. Note the arrangement of the pleura and pleural cavity (space) and the fibrous and the serous pericardia.
The pleurae and lungs lie on either side of the mediastinum within the chest cavity (Fig. 3.3).
Before discussing the
pleurae, it might be helpful to look at the illustrations of
the development of the lungs in Figure 3.4.
Each pleura has two parts:
- a parietal layer
- a visceral layer
What does the parietal layer lines?
a parietal layer, which lines
the thoracic wall,covers the thoracic surface of thediaphragm
and the lateral aspect of the mediastinum and
extends into the root of the neck to line the undersurface
of the suprapleural membrane at the thoracic outlet
What is the visceral layer?
visceral layer, which completely covers the outer surfaces
of the lungsandextends into the depths of the interlobar
fissures
What is the pulmonary ligament?
The two layers of the pleura become continuous with one another by means of a cuff of pleura that surrounds the structures
entering and leaving the lung at the hilum of each lung
(Figs. 3.3, 3.4, and 3.5).
To allow for movement of the pulmonary
vessels and large bronchi during respiration, the
pleural cuff hangs down as a loose fold called the pulmonary ligament
What is pleural cavity?
The parietal and visceral layers of pleura are separated
from one another by a slitlike space, the pleural cavity
(Figs. 3.3 and 3.4).