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Have a Heart
The idea for this week's experiment came to me while I
was moving our stuff into the hotel where we will be staying for the next 3
weeks. The room is on the second floor and we do not travel light. Basically
we take everything except the kitchen sink. We would probably take that as
well, but it is too hard to disconnect. After the 14th trip up the stairs, I
started to think about muscles and how they get tired. One thing lead to
another, and soon I had this week's experiment written. Why do your muscles get
tired? And more important, why does your heart, which is also a muscle, not get
tired?
To find out, you will need:
Your heart is a group of muscles which pump the blood
through your body. To get an idea of its size, make a fist. That is about the
same size as your heart. Pretending for a minute that your fist is your heart,
lets take the idea a little farther. Open you hand about half way and then
close it again. If you do that over and over, you can imagine that it is your
heart beating. You can even make heart sounds (bump-bump) if you (bump-bump)
want to. (bump-bump)
Keep this pretend heart beating as you read this. Soon
your hand will begin to get tired. If you keep opening and closing your hand
even after you are tired, it will begin to hurt. Why?
When you move your muscles, a chemical reaction takes
place. Normally, this chemical reaction needs oxygen. We get this oxygen when
we breath. The air moves into your lungs and the oxygen is absorbed by your
blood. Your blood carries the oxygen to your muscles. As long as the muscle
has plenty of oxygen, everything is fine and it can keep on moving.
If the muscle uses up oxygen faster than the blood can
deliver it, then what happens? The muscle does not instantly shut down when the
oxygen runs out.
Instead, a different chemical reaction takes over. It
lets your muscles move even if they do not have enough oxygen. The problem with
this backup system is that the reaction makes a chemical called lactic acid.
This acid irritates the muscle, making it hurt. If you overdo it, your muscles
will be sore the next day. Keep overdoing it and you can damage the muscle.
If your heart is made of muscle, why doesn't it get
tired? After all, your heart beats all day and all night, for your entire
life. A large part of the answer has to do with blood. Your heart is between
your lungs. Blood picks up oxygen from the lungs and flows directly to the
heart. This insures that the heart always has plenty of oxygen, so it does not
get tired. The one exception is if the blood vessels that lead to your heart
get blocked. Then the heart muscles run low on oxygen and get tired. The pain
that you feel is what tells you that you are having a heart attack.
Athletes exercise regularly to increase the blood
flowing to their muscles. If the muscles get more blood, they get more oxygen.
Then they can work harder and longer before they get tired. Right now, I could
use some extra oxygen, so I could unload the rest of our stuff.
Have a good
week.
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