The image reproduced here shows the bronchial tree demonstrated by the radiological procedure known as bronchography. X-ray opaque material is aspirated into the respiratory system to reveal the shape of the major branches of the tree. Note that the X-ray has been taken obliquely from the side to show the air passages to best advantage against the thoracic skeleton.
The trachea is the continuation of the conducting portion of the respiratory system below the larynx. It lies in the neck anterior to the oesophagus and branches to form the right and left primary or principal bronchi. The right bronchus is shorter, wider and more vertical than the left and so the right bronchus will normally be the site of inhaled foreign objects.
The primary bronchi branch to form the secondary or lobar bronchi (three on the right and two on the left). The lobar bronchi branch regularly to give rise to tertiary or segmental bronchi (ten on each side). As the segmental bronchi branch repeatedly, the diameter of the air passages and the cartilage content decrease. Distally, the arbitrary division between a bronchus and a bronchiole is based on the presence or absence of cartilage in the wall.
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