Chromosome: An organized structure of DNA found in cells. Chromosomes help maintain the integrity of DNA’s genetic code and regulate when genes are turned on or off. Human cells have 22 pairs of chromosomes called autosomes and two sex chromosomes, X or Y. Half the autosomes and one sex chromosome come from each of one’s parents.
Chronic bronchitis: A chronic inflammation of the bronchi, the medium-size airways in the lungs. The disease, one of two forms of chronic obstructive pulmonary disorder (COPD), is characterized by a persistent cough and an excess production of mucus.
Chronic obstructive pulmonary disease (COPD): A progressively worsening lung disease, the symptoms of which include an overproduction of mucus, shortness of breath, wheezing, and chest tightness. COPD is caused by smoking or long-term exposure to other environmental irritants such as air pollution and chemical fumes. See also, COPD under "Learn More."