Lungs

lung The respiratory organ of air-breathing vertebrates. A pair of lungs is situated in the thorax, within the ribcage. Each consists essentially of a thin moist membrane that is folded to increase its surface area. Exchange of oxygen and carbon dioxide takes place between blood capillaries on one side of the membrane and air on the other. The lung is supplied with air through a bronchus. The lungs are covered by a thin tissue layer called the pleura. The same kind of thin tissue lines the inside of the chest cavity -- also called pleura. A thin layer of fluid acts as a lubricant allowing the lungs to slip smoothly as they expand and contract with each breath.

Bronchitis

Bronchitis is a respiratory disease in which the mucus membrane in the lungs' bronchial passages becomes inflamed.
As the irritated membrane swells and grows thicker, it narrows or shuts off the tiny airways in the lungs, resulting in coughing spells that may be accompanied by phlegm and breathlessness. The disease comes in two forms: acute (lasting from one to three weeks) and chronic (lasting at least 3 months of the year for two years in a row). People with asthma may also have asthmatic bronchitis, inflammation of the lining of the bronchial tubes.