Yup. About 20 times a minute, you breathe in. When you do,

you inhale air and pass it through your nasal passages

where the air is filtered, heated, moistened and enters the

back of the throat. Interestingly enough, it's the

esophagus or foodpipe which is located at the back of the

throat and the windpipe for air which is located at the

front. When we eat, a flap -- the epiglottis -- flops down

to cover the windpipe so that food doesn't go down the

windpipe.

So -- back to breathing -- the air has a long journey to

get to your lungs. It flows down through the windpipe, past

the voice box or vocal cords, to where the lowermost ribs

meet the center of your chest. There, your windpipe divides

into two tubes which lead to the two lungs which fill most

of your ribcage. Inside each of your sponge-like lungs,

tubes, called bronchi, branch into even smaller tubes much

like the branches of a tree. At the end of these tubes are

millions of tiny bubbles or sacs called aleoli. Spread out

flat, all the air sacs in the lungs of an adult would cover

an area about the third of a tennis court.