The Human Respiratory System - Computational Fluid and Particle Dynamics in the Human Respiratory System - page 23

Fig. 2.5 Frontal view of a
human face showing the
locations of the paranasal
sinuses: frontal, ethmoid, and
maxillary sinuses

passage are the oval-shaped orifices of the posterior nares, ( choanae ) approximately
1.5-3.0 cm in diameter. The choanae are openings that allow air to pass from the
main nasal passage, into the nasopharynx. Once air has passed through the posterior
nares, it has left the nasal cavity and enters the next major segment of the upper
respiratory tract—the pharynx (Fig. 2.5 ).
The paranasal sinuses are four pairs of empty air spaces that open or drain into
the nasal cavity. They are located in the frontal, sphenoid, ethmoid, and maxillary
bones and as such their names are taken from where they are located. The frontal
sinuses are located just above the orbit (eye sockets) and don't develop until around
the age of seven. The maxillary, the largest of the sinuses extends laterally (into
the maxilla) on either side of the nose and is present at birth and grows with the
body's development. The sphenoid sinuses lie in the body of the sphenoid bone,
deep in the face just behind the nose. This sinus does not develop until adolescence.
The ethmoid sinuses are not single large cavities but rather a collection of small air
pockets, located around the area of the bridge of the nose. This sinus is also present
at birth, and grows with development.

2.2.2 Physiology of the Nose and Nasal Cavity

The nose and its internal nasal cavity provides a passageway for the air to pass
through to the lungs, warms and moistens (humidifies) the inhaled air, filters and
cleans the inhaled air from any foreign particles, resonates sounds for speech, and
houses the olfactory receptors for smell. At the entrance of the nasal cavity in the
vestibule region, the surface wall is made up of stratified squamous epithelium (same
as the external skin) which contains sebaceous glands, and nose hairs ( vibrissae ),
serving to filter out inhaled particulates. In the main nasal passage the walls are
lined with respiratory mucosa . This is made up of a pseudo stratified ciliated