LADY BRACKNELL: . . . Do you smoke?
JACK: Well, yes, I must admit I smoke.
LADY BRACKNELL: I am glad to hear it. A man should always have an occupation of some kind. There are far too many idle men in London as it is.
Oscar Wilde, The Importance of Being Earnest
Lungs deliver oxygen to the body, remove carbon dioxide waste, regulate temperature and stabilize blood pH balance.
To prevent lung tissues from drying out and to prevent infections, mucus is produced consisting of proteins, salts and immune system components suspended in water. Increased mucus production in the respiratory tract is stimulated in response to many diseases, such as the common cold. However, one disease called cystic fibrosis results in the mucus becoming too viscous, therefore impeding breathing.
The lungs also contain white blood cells which release a powerful enzyme called elastase which breaks down invading pathogens but not the normal lung tissues which are protected by a second protein called alpha-1-antitrypsin. However, disruptions to this second protein can lead to lung damage and emphysema known as alpha-1-antitrypsin deficiency. Smoking also inhibits alpha-1-antitrypsin.
A further inflammatory lung disease known as sarcoidosis occurs when the immune cells collect and damage specific areas of the lungs.