Section III. THE RESPIRATORY SYSTEM
The respiratory system figure 3-15) consists of the nose, pharynx, larynx,
trachea, bronchi, and the lungs (in which are found the bronchioles and the alveoli, or
air sacs). The primary function of the respiratory system is to supply the blood with
oxygen from the outside air and to effect the elimination of carbon dioxide from the
blood to the outside air. The exchanges between the air and the blood take place in the
alveoli of the lungs, which are the essential structures of respiration. The mechanics of
respiration will be discussed in greater detail later in this lesson.
3-21. THE NOSE AND PARANASAL SINUSES
a. The nose is composed of bone and cartilage. On the undersurface of the
external nose are two orifices, the nares. The nasal cavity is divided by the median
nasal septum into the right and left nasal chambers. The chambers communicate with
the exterior anteriorly by means of the nares and with the nasopharynx posteriorly by
means of the conchae.
b. On the lateral wall of each nasal chamber are three nasal conchae. Under
each concha is a meatus. Opening into each nasal chamber are the paranasal sinuses
(figure 2-35), which are named according to the bone in which each is located. The
ethmoidal sinuses, the maxillary sinuses, and the frontal sinuses open into the nasal
cavity. The opening of the sphenoidal sinus is above the superior meatus. Inhaled air
is warmed, moistened, and filtered by the nasal cavity. The filtering is done by cilia, the
hair of the mucous membrane, lining the nasal passages.
3-22. THE PHARYNX
The pharynx is a common passageway for air and food and, therefore, is also a
part of the digestive system. The oral and laryngeal parts have been discussed. The
two conchae, which are separated by the nasal septum, communicate with the pharynx
3-23. THE LARYNX
The larynx, or voice box, is in the upper and front part of the neck. It is the
passageway that connects the pharynx and the trachea. Its supporting framework is
made up of nine cartilages: the single thyroid cartilage, cricoid cartilage, epiglottic
cartilage, and the paired arytenoid, corniculate, and cuneiform cartilages. The epiglottis
guards the entrance to the larynx.