Human Anatomy and Physiology - I. V. Gayvoronsky 2011

Anatomy and Physiology of the Respiratory System
Upper Respiratory Tract

The External Nose, nasus externus (Greek: rhis, rhinos), is a triangular pyramid-shaped Structure located in the central part of the face. Its main anatomical parts include the ROOT, bridge, apex, and two alae (wings). The "Skeleton" of the external nose is formed by the nasal bones, the frontal processes of the Maxilla, and several nasal cartilages (Fig. 8.2). The latter include the lateral nasal Cartilage, the greater alar cartilage, 1–2 lesser alar cartilages, and accessory nasal cartilages. The root of the nose has a bony framework and is separated from the forehead by a depression known as the nasion. The alae have a cartilaginous framework and bound the anterior openings known as the nares (nostrils), through which air flows into and out of the Nasal cavity. The shape of the external nose is individual, yet it exhibits distinct ethnic characteristics. The exterior of the nose is covered by Skin, while internally the nares lead into a chamber called the nasal vestibule.

The nasal cavity, cavitas nasi, opens anteriorly through the nares and communicates posteriorly with the nasopharynx through apertures known as choanae. The nasal cavity comprises four walls: superior, inferior, and lateral. These are formed by the cranial bones and are described in section 4.3. The nasal septum runs along the midline; its "skeleton" consists of the perpendicular plate of the Ethmoid bone, the Vomer, and the septal cartilage. It should be noted that in approximately 90% of people, the nasal septum deviates from the midline to a greater or lesser extent. Minor ridges and depressions may be present on its surface, but a deviated septum is considered pathological only when it obstructs normal nasal breathing.

The nasal cavity is divided into the vestibule and the nasal cavity proper, separated by the limen nasi (nasal threshold). The limen nasi is an arched line on the lateral wall of the nasal cavity, located approximately 1 cm from the margin of the nares. The vestibule is lined with skin and covered with hairs that prevent large dust particles from entering the respiratory tract.

The nasal cavity contains three nasal conchae (turbinates): superior, middle, and inferior (Fig. 8.3). The bony framework of the first two is formed by the corresponding PARTS OF THE ethmoid bone, whereas the Inferior nasal concha is an independent bone. Beneath each nasal concha lie the superior, middle, and inferior nasal meatuses, respectively. The common nasal meatus is located between the lateral edge of the conchae and the nasal septum. Both laminar and turbulent airflow patterns occur within the nasal cavity. Laminar flow refers to smooth air movement without vortex formation, whereas turbulent flow is facilitated by the nasal conchae. This turbulence reduces the velocity of airflow through the nasal cavity; slower movement ensures better warming and purification of the air stream, creating optimal conditions for Gas Exchange in the alveoli. The nasolacrimal canal opens into the inferior nasal meatus, draining tears from the Lacrimal Apparatus into the nasal cavity.

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Fig. 8.2. External nose:

1 — lesser alar cartilage; 2 — anterior nasal spine of the maxilla; 3 — septal cartilage of the nose; 4 — nasal vestibule; 5 — greater alar cartilage; 6 — lateral cartilage; 7 — Nasal bone; 8 — frontal process of the maxilla; 9 — nasal part of the Frontal bone

Fig. 8.3. Nasal cavity:

1 — frontal sinus; 2 — sphenoid sinus; 3 — superior nasal concha; 4 — middle nasal concha; 5 — inferior nasal concha; 6 — pharyngeal opening of the auditory tube; 7 — inferior nasal meatus; 8 — nasal vestibule; 9 — middle nasal meatus; 10 — superior nasal meatus

The walls of the nasal cavity are lined with a mucous membrane, which is divided into respiratory and olfactory regions. The olfactory region is located within the superior nasal meatus and the superior nasal concha, housing the receptors of the Olfactory Organ, known as the olfactory bulbs.

The epithelium of the respiratory region is ciliated Cytology/practical/33.html">Pseudostratified columnar epithelium containing ciliated and goblet Cells. The goblet cells secrete mucus, which keeps the nasal cavity continuously moisturized. The surface of the ciliated cells features specialized micro-appendages called cilia. The cilia beat at a specific frequency, helping to propel mucus—along with trapped Bacteria and dust particles—toward the Pharynx. Vascular plexuses located in the deep layers of the mucous membrane provide warming for the incoming air.

Nasal breathing is much more physiological than Mouth breathing. In the nasal cavity, the air is purified, moistened, and warmed. Normal nasal breathing also ensures an individual's characteristic voice timbre.

Paranasal Sinuses are air-filled cavities within the Skull bones that are lined with mucous membrane and communicate with the nasal cavity via small channels. These channels open into the superior and middle nasal meatuses. The paranasal sinuses include:

✵ the maxillary sinus (antrum of Highmore), sinus maxillaris, located in the body of the maxilla;

✵ the frontal sinus, sinus frontalis, located in the frontal bone;

✵ the sphenoid sinus, sinus sphenoidalis, located in the body of the Sphenoid bone;

✵ the ethmoidal cells (anterior, middle, and posterior), cellulae ethmoidales, located within the ethmoid bone.

The paranasal sinuses develop During the first years of life. At birth, only the maxillary sinus is present (as a small cavity). The primary function of the paranasal sinuses is to provide vocal Resonance.

From the nasal cavity, the inhaled air passes through the nasopharynx and oropharynx into the Larynx. The Anatomical and physiological Features of the pharynx have been described previously.