The luminal surface of the vocal cords is covered with stratified squamous epithelium, as is most of the epiglottis (Plate 70, page 690). The epithelium serves to protect the mucosa from abrasion caused by the rapidly moving air stream. The rest of the larynx is lined with the ciliated, pseudostratified columnar epithelium that characterizes the respiratory tract (see Fig. 19.5 and Plate 70, page 690). The connective tissue of the larynx contains mixed mucoserous glands that secrete through ducts onto the laryngeal surface.
The trachea is a short, flexible, air tube about 2.5 cm in diameter and about 10 cm long. It serves as a conduit for air; additionally, its wall assists in conditioning inspired air. The trachea extends from the larynx to about the middle of the thorax, where it divides into the two main (primary) bronchi. The lumen of the trachea stays open because of the arrangement of the series of cartilaginous rings.
vestibule of the larynx stratified squamous epithelium
FIGURE 19.5 • Photomicrograph of a frontal section of the larynx. a. This photomicrograph shows three parts of the larynx: the vestibule above the ventricular folds, the ventricles between the vestibular folds and superior to the vocal folds, and the infraglottic cavity that extends from the vocal folds to the cricoid cartilage. Note that mucous glands are prominent in the ventricular folds and are covered by the typical pseudostratified ciliated epithelium. The vocal fold is composed of the epithelium, vocal ligament, and underlying vocalis muscle. Numerous lymph nodules are also present within the mucosa of the larynx (arrows). 10. b. High magnification of the area of the ventricular fold indicated by the upper rectangle in a shows on the left the pseudostratified ciliated epithelium that lines most of the larynx. Many nonsmoking adults and virtually all smokers exhibit patches of stratified squamous epithelium, as seen on the right of the micrograph. 240. c. High magnification of the area of the vocal fold indicated by the lower rectangle in a reveals normal stratified squamous epithelium at this site. Just beneath the epithelium is the connective tissue known as Reinke’s space. This clinically important site lacks lymphatic vessels and is poorly vascularized. The vocal ligament, inscribed by the dashed line, is seen at the bottom of the micrograph. 240.
The wall of the trachea consists of four definable layers:  Mucosa, composed of a ciliated, pseudostratified epithelium and an elastic, fiber-rich lamina propria  Submucosa, composed of a slightly denser connective tissue than the lamina propria  Cartilaginous layer, composed of C-shaped hyaline cartilages  Adventitia, composed of connective tissue that binds the trachea to adjacent structures
A unique feature of the trachea is the presence of a series of C-shaped hyaline cartilages that are stacked one on top of each other to form a supporting structure (Fig. 19.6). These cartilages, which might be described as a skeletal framework, prevent collapse of the tracheal lumen, particularly during  FOLDER 19.1 Clinical Correlation: Squamous Metaplasia in the Respiratory Tract