Respiratory Tract and Thorax

Trachea: The trachea is a cartilaginous and fibromuscular tube that extends from the inferior aspect of the cricoid cartilage (sixth cervical vertebra level) to the main carina (fifth thoracic vertebra level). Its length is 1012 cm in adults (of which 2-4 cm is extrathoracic and 6-9 cm intrathoracic). The tracheal wall has four different layers: mucosa, submucosa, cartilage or muscle, and adventitia. The posterior tracheal wall lacks cartilage and instead is supported by a thin band of smooth muscle.