When your child breathes in, air
fills the airways in the lungs. Oxygen-rich air reaches the balloon-like air sacs
end of the airways. These sacs are called alveoli. Oxygen passes into the blood vessels
around the sacs. The blood then carries the oxygen to all parts of the body. As the
uses oxygen, it makes a waste gas (carbon dioxide). The blood carries that back to
lungs. When your child breathes out, carbon dioxide leaves the body through the airways,
windpipe, and mouth or nose.