The Human Respiratory System - Computational Fluid and Particle Dynamics in the Human Respiratory System - page 28

correct passageway, either the oesophagus or the trachea, by being controlled by the
epiglottis. The epiglottis is a flap of elastic cartilage tissue that acts as a lid to cover
the trachea when food is swallowed in order to prevent objects entering the larynx
(see later Sect. 2.4 Larynx). During swallowing, the soft palate and its uvula point
upwards closing the nasopharynx so that neither air nor food can pass through it,
thus breathing is momentarily stopped. The connection opens and closes to equalise
the air pressure in the middle ear to that of the atmosphere for the conduction of
sound. The surface of the nasopharynx is covered by pseudo-stratified columnar ep-
ithelium. This is the same epithelium found in the nasal cavity and similarly the same
mechanism of mucous secretion from goblet cells in the epithelium to filter, warm,
and humidify the inhaled air occurs here. In the oropharynx and laryngopharynx,
the surface is lined with non-keratinizing stratified squamous epithelium which is
needed as it is exposed to food moving through the passageway.

2.3.3 Variations and Disease of the Pharynx

Some disease of the pharynx that may have an effect on the airway geometry and
airflow includes:
• Pharyngitis—Inflammation of the pharynx, which can be acute or chronic with

many different causes such as bacteria or viruses. This can result in swelling and
redness of the oropharynx and enlarged tonsils, restricting the passageway for
breathing and swallowing.

• Tonsillitis—Inflammation of the tonsils, which is commonly caused by viral or

bacterial infection. The tonsils become enlarged and this restricts the airway
opening from the oral cavity to the oropharynx, causing breathing and swallowing
problems.

• Pharyngeal Cancer—Cancer arising in the pharynx from the squamous epithelial

cells can restrict the airway, altering the natural flow of air in the pharynx.

2.4 Larynx

2.4.1 Anatomy of the Larynx

The larynx is commonly known as the voice box as it houses the vocal folds that are
responsible for sound production ( phonation ). It serves as a sphincter in transmitting
air from the oropharynx to the trachea and also in creating sounds for speech. It
is found in the anterior neck, connecting the hypopharynx with the trachea, which
extends vertically from the tip of the epiglottis to the inferior border of the cricoid
cartilage (Fig. 2.9 ). At the top of the larynx is the epiglottis which acts as a flap that