1.2 Energy subsystem phonation
1.2.1 Respiratory system: the lungs, bronchi, and trachea
The lungs have a sponge like and soft texture and are honeycombed with epithelium, having a 50 times larger surface area in total than the outer surface of human skin.
The airways are divided into an upside-down tree like structure with trachea and bronchi, the trachea divides into the two main bronchi that enter the roots of the lungs. The bronchi continue to divide within the lung, and after multiple divisions, give rise to bronchioles.
The trachea has an inner diameter of about 25 millimetres (1.0 in) and a length of about 10 to 16 centimetres (4 to 6 in). There are about fifteen to twenty incomplete C-shaped cartilaginous rings that reinforce the anterior and lateral sides of the trachea to protect and maintain the airway, leaving a membranous wall (pars membranacea) dorsally without cartilage.