Infraglottic Structures (Larynx, Trachea & Bronchi)

The Larynx

It is situated at the upper end of the respiratory tract, where it extends from the epiglottis to the lower end of the cricoid cartilage opposite to the 4th, 5th and 6th cervical vertebrae. It protects the lower respiratory tract from alimentary contents and is an organ of speech (Figure 3.3 and 3.4). It is composed of a number of cartilages which are joined together by ligaments. The movement of the cartilages is controlled by muscles. The principal cartilages are the thyroid, cricoid, and posterior (arytenoid, corniculate, and cuneiform) cartilage and the epiglottis. The laryngeal inlet is bounded anteriorly by the epiglottis, laterally by the aryepiglottic folds and posteriorly by the mucous membrane between the arytenoid cartilages.


Figure 3.3 The larynx and trachea structures

Vocal cords: These are two pearly white structures stretching from the angle of the thyroid cartilage in front to the vocal processes of the arytenoids behind (Figure 3:4). They are pale in color because they do not have the usual sub mucus tissue with blood vessels. In adults the narrowest portion of the larynx is the opening between the vocal cords. In children below the age of 10 years the narrowest portion is at the level of the cricoid cartilage. The cricoid cartilage is a complete ring that articulates with the thyroid and arytenoid cartilage. During inspiration the laryngeal inlet is opened. The cords are abducted. During expiration the cords are adducted and the opening is closed. The vestibular folds or the false vocal cords lie above the true vocal cords.


Figure 3.4 The laryngoscope view of the larynx

The Vallecula is depressions between the median and lateral glossoepiglottic folds that connect the lateral edges of the epiglottis to the base of the tongue (Figure3:4). During usage of Macintosh laryngoscope blade the tip of the laryngoscope is put into the vallecula, where it tensions the hyoepiglottic ligament to achieve indirect elevation of the epiglottis.

The laryngeal muscles can be grouped according to their actions on the vocal cords: abductors, adductors, and regulators of tension. The blood supply of the larynx is derived from branches of the thyroid arteries

The Cricothyroid Membrane joins the thyroid with the adjacent cricoid cartilage. It is close to the skin, relatively avascular, and the widest gap between the cartilage of the larynx and trachea, so it provides the best access for percutaneous (cricothyrotomy) airway rescue techniques. This technique is used in emergency condition when intubation and ventilation are impossible with the usual methods. It is normally easy to palpate, but identification may not be possible in obese patients.

Motor innervations to these muscles and the sensory innervations of the larynx are supplied by two branches of the vagus nerve: the superior and recurrent laryngeal nerves. The superior laryngeal branch of the vagus divides into an external (motor) nerve and internal (sensory) laryngeal nerves that provide sensory supply to the larynx between the epiglottis and the vocal cords. Another branch of the vagus, the recurrent laryngeal nerve, innervates the larynx below the vocal cords and the trachea.

Points to Remember:

  • To avoid injury to the cords extubate the patient during inspiration (cords abducted).
  • Topical analgesia (local anaesthetic) applied to the larynx may block the sensory branches of the superior and recurrent laryngeal nerves. This may result in a gruff voice and a change in the shape of the vocal cords.
  • The superior laryngeal or the recurrent laryngeal nerves may be injured during thyroid surgery. This injury may produce varying degrees of respiratory obstruction from hoarseness of voice to complete obstruction of the airway.
The Trachea and Bronchi

Trachea extends from the lower edge of the cricoid cartilage to the carina (extends from the 6th cervical to the 5th thoracic vertebra, lying anterior to the esophagus). It consists of C-shaped cartilage joined by fibroelastic tissue and is closed posteriorly by the longitudinal trachealis muscle (Figure3.3). 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, at the carina the trachea branches into the right and left primary bronchi. The right bronchus is wider, shorter and more vertical than the left. This has implications for the anesthetist in the following statements

  • An endotracheal tube or a tracheostomy tube which is too long will pass from the trachea into the right main bronchus.
  • Inhaled material e.g. vomitus has a greater tendency to gravitate into the right side of the chest.
Last modified: Tuesday, 15 November 2016, 12:27 PM