The bronchi are the tubes which carry air from the trachea to the inner recesses of the lungs, where it can transfer oxygen to the blood in the alveoli. Two main bronchi, the right and left bronchus, branch off of the low end of the trachea in what is called the tracheal bifurcation. One bronchus extends into each of the right and left lung. The bronchi continue to divide into smaller passageways, called bronchioles, forming a tree- like network of branches which extends throughout the spongy lung tissue. The exterior of the bronchi are composed of elastic, cartilaginous fibres and feature annular reinforcements of smooth muscle tissue. The bronchi are able to expand during inspiration, to allow the lungs to expand, and contract during expiration as air is exhaled. Research Bronchi