Respiratory System
Learning objectives
1. Recognize major parts of the respiratory track: trachea, bronchi, bronchioles, terminal bronchioles, respiratory bronchioles, alveolar duct, and alveoli.
2. Understand the blood-air interface in the alveolus and know the function of the type I and II pneumocyte and alveolar macrophage.
The respiratory system functions in the exchange of gases between the external and internal environments. Major parts of the system include the nasal cavity, larynx, trachea, bronchi, and pulmonary alveoli. Some regions of the respiratory system are specialized for conduction of gases and other areas function primarily in the exchange of gases. Filtration mechanisms exist in both regions. The function of each part of the respiratory system is reflected in the structure of its wall: the type of epithelium and its apical modifications, intraepithelial and subepithelial glands, cartilaginous rings and plates, smooth muscle and elastic tissue, and the relationship of capillary endothelium to alveolar epithelium.
| Segment | Characteristics |
| Conducting | |
| Trachea | Cartilage rings, pseudostratified ciliated epithelium with goblet cells, glands in submucosa |
| Bronchi | Plates of cartilage, smooth muscle, pseudostratified ciliated epithelium with goblet cells, glands may be present |
| Bronchioles | No cartilage, smooth muscle, no glands
Larger: pseudostratified ciliated epithelium with goblet cells Smaller: simple columnar or cuboidal, ciliated epithelium Terminal: Simple cuboidal ciliated epithelium with non-ciliated Clara (club) cells |
| Respiratory | |
| Bronchioles | Alveoli form out-pocketings from walls of bronchiole, smooth muscle in non-respiratory portions of walls
Initial segment: both ciliated and Clara (club) cells Distal segment: Clara (club) cells predominate |
| Alveolar ducts and alveoli | Squamous epithelium (type I pneumocytes), surfactant cells (type II pneumocytes), macrophages |