Bronchitis. Cutaway artwork of a lung showing the effects of bronchial inflammation (bronchitis). The airways of the lungs (bronchi), respond to an infection by becoming inflamed and producing mucus that is coughed up as sputum (phlegm, yellow). The mucus is seen inside the bronchi of the left lung (at right). Bronchitis also causes shortness of breath because the airways become narrowed. It is associated with both smoking and air pollution. With chronic bronchitis there is no cure and the functioning of the lungs steadily becomes reduced. The heart (lower left), pulmonary arteries (blue, centre left), vena cava veins (blue, far left) and the aorta (main body artery, red) are also seen.