The trachea is a fibroelastic tube with 15-20 C-shaped slightly separated cartilaginous rings along its length. The cartilages are aligned with each other and posteriorly, where the trachea is apposed to the oesophagus, they are deficient. This space is filled by the trachealis muscle. The hyaline cartilage helps to maintain the patency of the central lumen during inspiration.
The wall can be divided into four layers:
- mucous membrane:
- ciliated pseudostratified columnar epithelial cells; cilia move particles on 'mucociliary escalator' superiorly towards pharynx
- interspersed with:
- goblet cells; role in mucous secretion
- basal cells; progenitor of other cell types
- brush cells and dense core granule cells; possible role in sensation
- ducts of submucosal glands
- rests on lamina propria; has network of elastin fibres
submucosa:
þþ mixed seromucous glands; open via ciliated ducts into trachea
- lymphatic nodules
- cartilaginous smooth muscle layer:
- hyaline cartilage rings deficient posteriorly
- spanning deficiency is trachealis muscle and external annular ligament
- posterior deficiency facilitates passage of a food bolus through the oesophagus
- most superficial layer is a fibroelastic membrane which is the main support in the regular sections where the cartilage is absent on descent of the trachea
- adventitia: fibrous layer that blends with the adventitia of the anterior oesophagus; the close association produced by the adventitia makes spread of malignancy more common between these two structures