We’re studying the lungs and the respiratory system this week. The miracle of our breathing always blows me away every time I teach this. It’s a miracle when a newborn baby takes its first breath, but every breath that you and I take is no less a miracle. Our lungs have about 700 million microscopic air sacs called alveoli. They would cover a tennis court if we could lay them all out side by side. Each alveolus is embraced by tiny capillaries through which only one red blood cell can flow at a time. In the fraction of a second that blood cells flow by each tiny air sac, they attract oxygen molecules through the fine delicate membrane that separates the blood from the air. All told, our blood cells absorb or extract about a cup of pure oxygen from the air in our lungs every minute of the day. Then our arteries carry this oxygen-rich blood to every cell in the body. Our vitality and our very lives are totally dependent on this incredible process that goes on 24 hours a day. It truly is miraculous.