The Trachea and Bronchi

The trachea (TRAY-kee-uh), or "windpipe," is a rigid tube about 12 cm (4.5 in.) long and 2.5 cm (1 in.) in diameter, lying anterior to the esophagus (fig. 22.7a). It is supported by 16 to 20 C-shaped rings of hyaline cartilage, some of which you can palpate between your larynx and sternum. Like the wire spiral in a vacuum cleaner hose, the cartilage rings reinforce the trachea and keep it from collapsing when you inhale. The open part of the C faces posteriorly, where it is spanned by a smooth muscle, the trachealis (fig. 22.7c). The gap in the C allows room for the esophagus to expand as swallowed food passes by. The trachealis muscles can contract or relax to adjust tracheal airflow. At its inferior end, the trachea branches into the right and left primary bronchi, which supply the lungs. They are further traced in the following discussion of the bronchial tree in the lungs.

The larynx, trachea, and bronchial tree are lined mostly by ciliated pseudostratified columnar epithelium (figs. 22.7b and 22.8), which functions as a mucociliary escalator. That is, the mucus traps inhaled debris and then the ciliary beating drives the mucus up to the pharynx, where it is swallowed.

Insight 22.1 Clinical Application

Tracheostomy

If the airway is obstructed with secretions or foreign matter, it may be necessary to make a temporary opening in the trachea inferior to the larynx and insert a tube to allow airflow—a procedure called tracheostomy. This prevents asphyxiation, but the inhaled air bypasses the nasal cavity and thus is not humidified. If the opening is left for long,

Saladin: Anatomy & I 22. The Respiratory System I Text I © The McGraw-Hill

Physiology: The Unity of Companies, 2003 Form and Function, Third Edition

Chapter 22 The Respiratory System 847

Adduction of vocal cords

Abduction of vocal cords

Adduction of vocal cords

Cricoarytenoid Ligament
(a)

Thyroid cartilage-Cricoid cartilage-Vocal cord Lateral cricoarytenoid muscle Arytenoid cartilage Corniculate cartilage Posterior cricoarytenoid muscle

Abduction of vocal cords

Anterior i i

Posterior

Anterior i i

Posterior

Base of tongue Epiglottis Vestibular fold Vocal cord Glottis

Corniculate-cartilage

Epiglottis Arytenoid Fold Esophagus

Figure 22.6 Action of Some of the Intrinsic Laryngeal Muscles on the Vocal Cords. (a) Adduction of the vocal cords by the lateral cricoarytenoid muscles. (b) Adducted vocal cords seen with the laryngoscope. (c) Abduction of the vocal cords by the posterior cricoarytenoid muscles. (d) Abducted vocal cords seen with the laryngoscope.

Base of tongue Epiglottis Vestibular fold Vocal cord Glottis

Corniculate-cartilage

Figure 22.6 Action of Some of the Intrinsic Laryngeal Muscles on the Vocal Cords. (a) Adduction of the vocal cords by the lateral cricoarytenoid muscles. (b) Adducted vocal cords seen with the laryngoscope. (c) Abduction of the vocal cords by the posterior cricoarytenoid muscles. (d) Abducted vocal cords seen with the laryngoscope.

the mucous membranes of the respiratory tract can dry out and become encrusted, interfering with the clearance of mucus from the tract and leading to severe infection. We can understand the functional importance of the nasal cavity especially well when we see the consequences of bypassing it.

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