The Larynx and trachea

The Larynx

The larynx or “voice box” is a cartilaginous chamber about 4 cm (1.5 in.) long. Its primary function is:

• Maintain an open passageway for air movement.
• Epiglottis and vestibular folds prevent swallowed material from moving into larynx.
• Vocal folds are primary source of sound production.

The superior opening of the larynx, the glottis,3 is guarded by a flap of tissue called the epiglottis.4 During swallowing, extrinsic muscles of the larynx pull the larynx upward toward the epiglottis, the tongue pushes the epiglottis downward to meet it, and the epiglottis directs food and drink into the esophagus dorsal to the airway. The vestibular folds of the larynx, discussed shortly, play a greater role in keeping food and drink out of the airway, however. People who have had their epiglottis removed because of cancer do not choke any more than when it was present.

In infants, the larynx is relatively high in the throat and the epiglottis touches the soft palate. This creates a more or less continuous airway from the nasal cavity to the larynx and allows an infant to breathe continually while swallowing. The epiglottis deflects milk away from the airstream, like rain running off a tent while it remains dry inside. By age two, the root of the tongue becomes more muscular and forces the larynx to descend to a lower position.

The framework of the larynx consists of nine cartilages:

• 1 Thyroid cartilage
• 1 Cricoid5 cartilage
• 1 Epiglottic cartilage
• 2 Arytenoid6 cartilages
• 2 Corniculate7  cartilages
• 2 cuneiform  cartilages

The first three are relatively large and unpaired. The most superior one, the epiglottic cartilage, is a spoon- shaped supportive plate in the epiglottis. The largest, the thyroid cartilage, is named for its shieldlike shape. It has an anterior peak, the laryngeal prominence, commonly known as the Adam’s apple. Testosterone stimulates the growth of this prominence, which is therefore significantly larger in males than in females. Inferior to the thyroid cartilage is a ringlike cricoid5 cartilage, which connects the larynx to the trachea.

The remaining cartilages are smaller and occur in three pairs. Posterior to the thyroid cartilage are the two arytenoid6 cartilages, and attached to their upper ends are a pair of little horns, the corniculate7  cartilages. The arytenoid and cuneiform cartilages function in speech, as explained shortly. A pair of cuneiform8 cartilages support the soft tissues between the arytenoids and the epiglottis. The epiglottic cartilage is elastic cartilage; all the others are hyaline.

The trachea:

The trachea, commonly called the windpipe, is a tube connecting the larynx to the primary bronchi. The trachea lies ventral to the esophagus and is held open by C-shaped carti- laginous rings. The open part of the C-shaped rings faces the esophagus, and this allows the esophagus to expand when swallowing. The mucosa that lines the trachea has a layer of pseudostratified ciliated columnar epithelium. (Pseudostrati- fied means that while the epithelium appears to be layered, actually each cell touches the basement membrane.) The cilia that project from the epithelium keep the lungs clean by sweeping mucus, produced by goblet cells, and debris toward the pharynx.

Smoking is known to destroy these cilia, and consequently the soot in cigarette smoke collects in the lungs.

If the trachea is blocked because of illness or the accidental swallowing of a foreign object, it is possible to insert a breathing tube by way of an incision made in the trachea. This tube acts as an artificial air intake and exhaust duct. The oper- ation is called a tracheostomy.