Chapter Summary

I. CONDUCTING PORTION

A. Nasal Cavity

1. Respiratory Region

The respiratory region is lined by respiratory (pseudostratified ciliated columnar) epithelium. The subepithelial connective tissue is richly vascularized and possesses seromucous glands.

2. Olfactory Region

The epithelium of the olfactory region is thick, pseudostratified ciliated columnar epithelium composed of three cell types: basal cell, sustentacular cells, and olfactory cells. The lamina propria is richly vascularized and possesses Bowman’s glands, which produce a watery mucus.

B. Larynx

The larynx is lined by a respiratory epithelium except for certain regions that are lined by stratified squamous nonkeratinized epithelium. From superior to inferior, the lumen of the larynx presents three regions: the vestibule, the ventricle, and the infraglottic cavity. The ventricular and vocal folds are the superior and inferior boundaries of the ventricle, respectively. Cartilages, extrinsic and intrinsic muscles, as well as mucous and seromucous glands are present in the larynx.

C. Trachea

1. Mucosa

The mucosa of the trachea is composed of a respiratory epithelium with numerous goblet cells, a lamina propria, and a well-defined elastic lamina.

2. Submucosa

The submucosa houses mucous and seromucous glands.

3. Adventitia

The adventitia is the thickest portion of the tracheal wall. It houses the C-rings of hyaline cartilage (or thick connective tissue between the rings). Posteriorly, the trachealis muscle (smooth muscle) fills in the gap between the free ends of the cartilage.

D. Extrapulmonary Bronchi

Extrapulmonary bronchi resemble the trachea in histologic structure.

E. Intrapulmonary Bronchi

These and subsequent passageways are completely surrounded by lung tissue.

1. Mucosa

Intrapulmonary bronchi are lined by respiratory epithelium with goblet cells. The subepithelial connective tissue is no longer bordered by an elastic lamina.

2. Muscle

Two ribbons of smooth muscle are wound helically around the mucosa.

3. Cartilage

The C-rings are replaced by irregularly shaped hyaline cartilage plates that encircle the smooth muscle layer.

Dense collagenous connective tissue connects the perichondria of the cartilage plates.

4. Glands

Seromucous glands occupy the connective tissue between the cartilage plates and smooth muscle. Lymphatic nodules and branches of the pulmonary arteries are also present.

F. Bronchioles

Bronchioles are lined by ciliated simple columnar to simple cuboidal epithelium interspersed with nonciliated Clara cells. Goblet cells are found only in larger bronchioles. The lamina propria possesses no glands and is surrounded by smooth muscle. The walls of bronchioles are not supported by cartilage. The largest bronchioles are about 1 mm in diameter.

G. Terminal Bronchioles

Terminal bronchioles are usually less than 0.5 mm in diameter. The lumen is lined by simple cuboidal epithelium (some ciliated) interspersed with Clara cells. The connective tissue and smooth muscle of the wall of the terminal bronchioles are greatly reduced.

II. RESPIRATORY PORTION

A. Respiratory Bronchiole

Respiratory bronchioles resemble terminal bronchioles, but they possess outpocketings of alveoli in their walls. This is the first region where exchange of gases occurs.

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B. Alveolar Ducts

Alveolar ducts possess no walls of their own. They are long, straight tubes lined by simple squamous epithelium and display numerous outpocketings of alveoli. Alveolar ducts end in alveolar sacs.

C. Alveolar Sacs

Alveolar sacs are composed of groups of alveoli clustered around a common air space.

D. Alveolus

An alveolus is a small air space partially surrounded by highly attenuated epithelium. Two types of cells are

present in the lining: type I pneumocytes (lining cells) and type II pneumocytes (produce surfactant). The opening of the alveolus is controlled by elastic fibers. Alveoli are separated from each other by richly vascularized walls known as interalveolar septa, some of which present alveolar pores (communicating spaces between alveoli). Dust cells (macrophages), fibroblasts, and other connective tissue elements may be noted in interalveolar septa. The blood-air barrier is a part of the interalveolar septum, the thinnest of which is composed of surfactant, continuous endothelial cells, type I pneumocyte, and their intervening fused basal laminae.

CHAPTER OUTLINE

Graphics

Graphic 13-1 Tooth and Tooth Development p. 308 Graphic 13-2 Tongue and Taste Bud p. 309

Tables

Table 13-1 Summary of the Oral Mucosa

Plates