Finally, in the bronchi, but not the bronchioles, there is also a layer of cartilage below the submucosa which stiffens the bronchus and helps to keep it open.
After the first three generations of bronchi, however, the airways become more narrow, called bronchioles - 'little bronchi', and these can stay open without the need for cartilage.
During inhalation, air reaches your lungs by traveling down your trachea, then it continues through the bronchi and the bronchioles and ends up in the alveoli.
The lower respiratory system begins with the larynx, or voice box, and includes the trachea, or wind pipe, bronchi, bronchioles, and alveoli within the lungs.
Occasionally in the sputum there might be curschmann spirals, which are spiral shaped mucus plugs or basically elongated mucous casts from small bronchi of people with bronchial asthma.
The trachea is part of the conducting zone, and it branches into right and left primary bronchi, carrying air to and from the right and left lung, respectively.