With Valentine's Day in February, the human heart can be a good science topic to explore. The heart is the major organ of the circulatory system which moves blood throughout our bodies. But this system is hard to look at alone because it works along with other parts of the body. Let's take a look at one of these other parts, or at two of them, the lungs.
If you asked most people what the lungs do, they would probably say that the lungs breathe in oxygen and breathe out carbon dioxide. This isn't really true. The lungs breathe in air and breathe out air. Want proof? If our lungs breathed in oxygen and breathed out carbon dioxide would it help someone who has stopped breathing to give them mouth to mouth resuscitation? Of course not! They would only get carbon dioxide. How could a crowd of people ride in a tiny elevator if we took all the oxygen from each breath we inhaled and exhaled only carbon dioxide? Everyone would soon faint.
What really happens? We breathe air into our lungs. The blood passing through the tiny capillaries in our lungs takes some of the oxygen out of the air and adds some carbon dioxide into our lungs. When we breathe out, the air that leaves our lungs has a little more carbon dioxide and a little less oxygen than it did. It also has a little more moisture in it. Our lungs are coated with moisture so that gases can move between them and our blood. You can see a little of this moisture when you blow your breath out on a cold day.
Once our blood is loaded with oxygen, it is pumped throughout our bodies so that our cells can get both oxygen and food. Inside our cells, oxygen is used to burn the food to release energy for the cell to survive. This controlled burning is called respiration. It makes heat which keeps our temperature up. It also makes wastes which must be gotten rid of by our lungs (carbon dioxide) when we breathe out, and by our kidneys and our intestines when we go to the bathroom.