Plate 66 Larynx

The larynx is the passageway for air between the oropharynx and the trachea that functions in the production of sound. It consists of a cartilaginous framework to which both extrinsic and intrinsic muscles are attached and a mucosal surface that varies in character from pseudostratified to stratified squamous in regions subject to abrasion by the air stream. The muscles move certain cartilages with respect to others, thus increasing or decreasing the opening of the glottis and increasing or decreasing the tension on the vocal folds (cords). In this way, vibrations of different wavelengths are generated in the passing air, and sound is produced.

Figure 1, larynx, monkey, H&E x15.

The vocal folds are ridge-like structures that are oriented in an anteroposterior (ventral-dorsal) direction. In frontal sections, the vocal folds (VF) are cross-sectioned, giving the appearance seen here. The two vocal folds and the space between them constitute the glottis. Just above each vocal fold is an elongated recess called the ventricle (V), and above the ventricle is another ridge called the ventricular

Figure 2, larynx, monkey, H&E x160.

The surfaces of a vocal fold and the facing ventricular fold within rectangle 1 in Figure 1 are turned 90° clockwise and shown at higher magnification in this figure. Medially, both are lined by stratified squamous epithelium (SSE).

fold (VnF) or, sometimes, the false vocal fold. Below and lateral to the vocal folds are the vocalis muscles (VM). Within the vocal fold is a considerable amount of elastic material, although it is usually not evident in routine H&E preparations. This elastic material is part of the vocal ligament. It lies in an anteroposterior direction within the substance of the vocal fold and plays an important role in phonation.

Here, the contact between surfaces is considerable. Laterally, the surfaces consist of stratified columnar epithelium (SCE). The contact between these surfaces is less wearing. Small glands (Gl) are in the lamina propria of the laryngeal mucosa.

Figure 3, larynx, monkey, H&E x160.

Rectangle 2 in Figure 1 is shown at higher magnification in this figure. It shows the junction between the stratified squamous epithelium (SSE), with its flat surface cells, and the stratified columnar epithelium (SCE), with its columnar surface cells. The lamina propria consists of loose connective tissue in which glands (Gl) are present.

Figure 4, larynx, monkey, H&E x160.

Just below the portion of the larynx shown in Figure 1, the epithelium changes again, giving way, below, to the ciliated pseudostratified columnar epithelium (PSE) shown here. Note the cylinders of cytoplasm that clearly indicate the columnar nature of the surface cells. In the upper part of the figure, the epithelium is stratified columnar; in the lower part of the figure, it is pseudostratified columnar. This distinction is difficult to make from the examination of a single sample such as that shown here, and other information is needed to make the assessment. The additional information is the presence of cilia on the pseudostratified columnar epithelium; this epithelium is typically ciliated. Although not evident in the photomicrographs, note that stratified columnar epithelium has a very limited distribution, usually occurring between stratified squamous epithelium and some other epithelial types (e.g., pseudostratified columnar here or simple columnar at the anorectal junction, Plate 60).The lamina propria is a loose cellular connective tissue, and it also shows some glands (Gl).

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