Figure 184

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). xlO. b. High magnification of the area of the ventricular fold indicated

dense connective tissue stratified squamous .epithelium dense connective tissue stratified squamous .epithelium vocal s

ligament vocal s

ligament 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. X240. 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. x240.

false vocal cords (see Fig. 18.5). These folds do not have the intrinsic muscular investment of the true vocal cords and, therefore, do not modulate in phonation. They and the ventricle, however, are important in creating sound resonance.

Stratified squamous and ciliated pseudostratified columnar epithelium line the larynx

The luminal surface of the vocal cords is covered with stratified squamous epithelium, as is most of the epiglottis.

In human respiratory mucosa, ciliated pseudostratified epithelium may change to stratified squamous epithelium. This transformation is a normal occurrence on the rounded, more exposed portions of the turbinates, on the vocal folds, and in certain other regions. Changes in the character of the respiratory epithelium may, however, occur in other ciliated epithelial sites when the pattern of airflow is altered or when forceful airflow occurs, as in chronic coughing. Typically, in chronic bronchitis and bronchiectasis, the respiratory epithelium changes in certain regions to a stratified squamous form. The altered epithelium is more resistant to physical stress and insult, but it is less effective functionally. In smokers, a similar epithelial change occurs. Initially, the cilia on ciliated cells lose their synchronous beating pattern due to noxious elements in smoke. As a result, removal of mucus is impaired. To compensate, the individual begins to cough, thereby facilitating the expulsion of accumulated mucus in the airway, particularly in the trachea. With time, the number of ciliated cells decreases because of chronic coughing. This reduction in ciliated cells further impairs the normal epithelium and results in its replacement with stratified squamous epithelium at affected sites in the airway.

Epithelial alterations of this kind are referred to as metaplasia, i.e., a reversible change from one type of fully differentiated adult cell to a different type of adult cell. A given mature cell does not change to another type of mature cell; rather, basal cell proliferation gives rise to the new differentiated cell type. These cellular changes are considered to be controlled and adaptive.

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.

18.4). The connective tissue of the larynx contains mixed mucoserous glands that secrete through ducts onto the laryngeal surface.

A Disquistion On The Evils Of Using Tobacco

A Disquistion On The Evils Of Using Tobacco

Among the evils which a vitiated appetite has fastened upon mankind, those that arise from the use of Tobacco hold a prominent place, and call loudly for reform. We pity the poor Chinese, who stupifies body and mind with opium, and the wretched Hindoo, who is under a similar slavery to his favorite plant, the Betel but we present the humiliating spectacle of an enlightened and christian nation, wasting annually more than twenty-five millions of dollars, and destroying the health and the lives of thousands, by a practice not at all less degrading than that of the Chinese or Hindoo.

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