Section of trachea (human, adult, high magnification)

Stain: Azan. On top: the epithelium (1) is pseudostratified with cilia and goblet cells (white droplets) on a distinct basement membrane (↓, undulating thick deep-red line) followed by a small proper lamina (2). The submucosa (3) starts where the fibrous tissue (elastic fibers reinforced with collagen) becomes denser and deep blue (elastic fibers are almost masked due the staining). Mixed seromucous tracheal glands (4) (left side) and an excretory duct (5) draining into an epithelial invagination are localized within the submucosa. Below the perichondrium (*) of hyaline cartilage (6) which artifactually is separated from the submucosa.