RESPIRATORY SYSTEM
The respiratory system is made up of the
structures involved in the exchange of oxygen and carbon dioxide between the
blood and the atmosphere, so-called external respiration. The exchange
of gases between the blood in the capillaries of the systemic circulation and
the tissues in which these capillaries are located is referred to as internal
respiration.
The respiratory system consists of the external nose, internal nose, and
paranasal sinuses; the pharynx, which is the common passage for air and food;
the larynx, where the voice is produced; and the trachea, bronchi, and lungs.
Accessory structures necessary for the operation of the respiratory system are
the pleurae, diaphragm, thoracic wall, and muscles that raise and lower the ribs in inspiration and expiration.
The muscles of the anterolateral abdominal wall are also accessory to forceful
expiration (their contraction forces the diaphragm upward by pressing the
contents of the abdominal cavity against it from below) and are used in
“abdominal” respiration. Certain muscles of the neck can elevate the ribs, thus
enlarging the anteroposterior diameter of the thorax, and under some
circumstances, the muscles attaching the arms to the thoracic wall can also
help change the capacity of the thorax.
In Plates 1-1 through 1-16, the anatomy of the respiratory system and
significant accessory structures is shown. It is important not only to visualize
these structures in isolation but also to become familiar with their blood
supply, nerve supply, and relationships with both adjacent structures and the
surface of the body. One should keep in mind that these relationships are
subject to the same degree of
individual variation that affects all anatomic structures. The illustrations
depict the most common situations encountered. No attempt is made to describe
all of the many variations that occur. An important and clinically valuable
concept that is worth emphasizing at this point is the convention of
subdividing each lung into lobes and segments on the basis of branching of the
bronchial tree. From the standpoint of its embryologic development, as well as
of its function as a fully established organ of respiration, the lung is indeed
the ultimate branching of the main bronchus that leads into it. Knowledge of
the subdivision of the lung on this basis is essential to anatomists,
physiologists, pathologists, radiologists, surgeons, and chest physicians
because without this three-dimensional key, there is no exact means of
precisely localizing lesions within
the respiratory system.
