They are important for lung function, since their purpose is the exchange of oxygen and carbon dioxide. When the airways are blocked by a mucous plug, foreign object, or tumor, the alveoli are unable to fill with air and collapse of lung tissue can occur in the affected area.
Testing Positive for Marijuana Does Not Indicate Impairment Someone can test positive for marijuana days or even weeks after they last used it. by Dr. Carl Hart @drcarlhart. AAs Oregonians consider their vote on tax and regulation of marijuana, it is important for them to have access to sound information grounded in science.
1 For moderate smokers it is 1-2 weeks. Frequent users can test positive more than 2 weeks, and in rare cases marijuana can stay in the system of heavy smokers more than a month.  Hair. This kind of test is less common and key factors do not have any impact on its marijuana detection time.