The trachea bifurcates forming the two principal bronchi. These branch to form lobar bronchi (which supply the lobes of the lungs i.e. three on the right and two on the left); these then undergo further divisions to form ten segmental bronchi on each side. Each segment of the lung is an independant functional unit. The airways continues to divide, becoming smaller with each division. The wall of the bronchus has the following components:
Respiratory epithelium lines the bronchus, it stains darkly purple in this section.
Lamina propria is a thin layer deep to the epithelium which cannot be distinguished in detail in this section. It is rich in elastic tissue and capillaries. Bundles of pink staining, smooth muscle fibres form a boundary between the lamina propria and the submucosa.
Submucosa contains serous bronchial glands which lie in groups between irregular sections of purple staining cartilage.
Cartilage becomes more irregular in shape as the airway divides and it may be seen as several blocks in a transverse section of the bronchial wall. As the bronchi continue to branch, the cartilage element is reduced until it finally disappears from the wall of the bronchioles.
Fibrous coat surrounds the bronchus. This section shows how the bronchus is embedded in respiratory tissue consisting of a network of alveoli.
SUPPLEMENTARY: