Tough cells and old age.
D000328:Adult; D000368:Aged; D000375:Aging; D001991:Bronchitis / Q000473:pathology; D002453:Cell Cycle; D002455:Cell Division; D002470:Cell Survival; D005260:Female; D006801:Humans; D008168:Lung / Q000473:pathology; D008297:Male; D008875:Middle Aged; D011656:Pulmonary Emphysema / Q000473:pathology; D012907:Smoking