Anita Baslock, age 10, of Huntsville, Ala., for her question:
DO ALL ANIMALS HAVE A HEART LIKE OURS?
The circulation of blood throughout the body depends on one tireless muscle the heart. Every day of the year it does its job, beating about 70 times per minute, 100,000 times a day. Though it weighs less than a pound and is only about the size of your fist, in a lifetime of 70 years it will pump enough blood to fill a skyscraper.
If we were going to divide all the animals into groups, we could do it in a number of ways. One of the easiest might be to put those with a backbone in one group and those without a backbone in another group. Some of the animals without backbones have hearts of sorts, but none of them has a heart like ours. Fish, frogs, snakes, birds and people belong to the group of animals that have a backbone, but even their hearts are different.
The circulatory system of any animal with a backbone is called a closed system. All the blood is contained in the heart and a network of large and small tubes called arteries and veins. In most cases tubes that bring blood to the heart are called veins, and tubes that carry blood away from the heart are called arteries.
The heart of a person is divided into four chambers. The two upper chambers are called atria, and the two lower chambers are called ventricles. The heart works by contracting and relaxing at a nice even pace. First the two upper chambers contract, forcing blood into the relaxed lower chamber. The lower chambers then contract, pumping the blood out to the body and the lungs in and out, in and out, all day long.
Most fish have a two chambered heart. This is the simplest kind of heart creatures with backbones have. Lungfish, however, are different from the other fish because they have a heart that contains three chambers. The frogs, toads and other amphibians have a three chambered heart like the lungfish.
Crawly snakes and most of their reptilian cousins have a three chambered heart like the toads and frogs. The toothy crocodiles and alligators are exceptions to the rule, for theyhave a four chambered heart. Birds have hearts similar to the alligators and crocodiles, except that theirs are a bit better developed. In mammals a group that includes dogs, cats, bears and many other animals the heart always has four chambers.
Many times when we visit our doctor he will listen to our heart through his stethoscope. What he hears is a sort of lub dub sound caused by the closing of valves inside the heart. And sometimes, if things aren't going just right, the sounds will be different and alert the doctor that corrective action is needed.