The breathing system takes in alveoliattackbloodbronchiolescancercapillariescarboncellsExhaledexpelledincreaseincreasesoxygentrachea and removes alveoliattackbloodbronchiolescancercapillariescarboncellsExhaledexpelledincreaseincreasesoxygentrachea dioxide. When we breathe in, alveoliattackbloodbronchiolescancercapillariescarboncellsExhaledexpelledincreaseincreasesoxygentrachea travels in the air through the alveoliattackbloodbronchiolescancercapillariescarboncellsExhaledexpelledincreaseincreasesoxygentrachea and bronchi, into the alveoliattackbloodbronchiolescancercapillariescarboncellsExhaledexpelledincreaseincreasesoxygentrachea and finally reaches numerous sac-like structures called alveoliattackbloodbronchiolescancercapillariescarboncellsExhaledexpelledincreaseincreasesoxygentrachea. The thin surfaces of the alveoli are in contact with alveoliattackbloodbronchiolescancercapillariescarboncellsExhaledexpelledincreaseincreasesoxygentrachea vessels called alveoliattackbloodbronchiolescancercapillariescarboncellsExhaledexpelledincreaseincreasesoxygentrachea. At the alveoli, oxygen enters the blood to be carried to alveoliattackbloodbronchiolescancercapillariescarboncellsExhaledexpelledincreaseincreasesoxygentrachea in the body. Waste carbon dioxide in the alveoliattackbloodbronchiolescancercapillariescarboncellsExhaledexpelledincreaseincreasesoxygentrachea is excreted at the alveoli and alveoliattackbloodbronchiolescancercapillariescarboncellsExhaledexpelledincreaseincreasesoxygentrachea in the air we breathe out. alveoliattackbloodbronchiolescancercapillariescarboncellsExhaledexpelledincreaseincreasesoxygentrachea air contains more carbon dioxide than inhaled air. The rate of breathing alveoliattackbloodbronchiolescancercapillariescarboncellsExhaledexpelledincreaseincreasesoxygentrachea with exercise. Smoking can alveoliattackbloodbronchiolescancercapillariescarboncellsExhaledexpelledincreaseincreasesoxygentrachea the risk of lung infection, alveoliattackbloodbronchiolescancercapillariescarboncellsExhaledexpelledincreaseincreasesoxygentrachea and heart alveoliattackbloodbronchiolescancercapillariescarboncellsExhaledexpelledincreaseincreasesoxygentrachea.