Trachea is thin walled, rigid tube continuing with larynx and terminates in two chief bronchi.
- The following layers are recognized:
- Mucosa
- Submucosa
- A layer of fibroelastic membrane with hyaline cartilage rings and
- Adventitia
- Mucosa
- It is lined by pseudostratified ciliated columnar epithelium with numerous Goblet cells between the ciliated columnar cells.
- The basement membrane is distinct.
- The lamina propria contains numerous elastic fibres and a fibro-elastic membrane may be formed in the deeper zone, separating the lamina propria form the submusosa.
- Submucosa
- It consists of loose connective tissue and contains, mixed or mucous glands.
- The framework of trachea consists of series of regularly arranged C-shaped rings of hyaline cartilage. The open segment of C is dorsal and between the free cartilage, smooth muscle bundles (trachealis) are present. Most of the muscle fibres are arranged transversely. A fibroelastic membrane, which blends with the perichondrium extends between the adjacent cartilages and also between the open ends of the cartilaginous rings enclosing the smooth muscle bundles. This fibro elastic membrane is called the tracheal annular ligament.
- The adventitia has collagenous and elastic tissue with adipose tissue and contains blood vessels and nerves.
- Species differences
- In the horse, ruminant and pig, the smooth muscle fibres lie inside the ends of rings of cartilage, but in the dog and cat they lie outside the ring. In man, it connects the two ends.
