Stan Christy, age 12, of Utica, N.Y., for his question:
How dons the heart beat?
The heart is a small four‑roomed house. The outer walls are made of thick, strong muscle and inside there is a center wall. This is a partition which divides the house into two separate parts, each part having a small upstairs room and a larger downstairs room. Even in a grown man, the heart is smaller than a grapefruit. For such a little house, it has a huge stack of chimneys. They are the blood vessels which lead the blood to and from the heart.
In a way, the heart really is a house. It is the powerhouse of the body. Its job is to keep the blood stream circulating. The blood carries oxygen and dissolved foods to the body calls and gathers up waste materials. Some of the body cells perish in a few moments without fresh oxygen. So the heart must keep the blood flowing around in a circuit day and night. The circuit is a wonderful network of blood vessels loading to each part of the body and back to the heart.
The blood leading from the heart is loaded with oxygen to deliver to the body calls. These blood vessels are the arteries. The blood leading back to the heart are veins. They have delivered their oxygen and picked up a load of waste carbon dioxide.
The heart is divided into two separate parts for a very good reason. The used blood in the veins must not mix with the fresh blood in the arteries. It must be sent to the lungs to be purified before it is sent on a trip through the arteries. The right side of the heart deals with the used blood ‑ receives the fresh blood from the lungs and pumps it on its way around the body.
The small upstairs rooms are called auricles. The layer downstairs rras are the ventricles. The heart works us a pump, relaxing and contracting. The upstairs tenses first, then the downstairs and the whole heart relaxes for a fraction of a second. There is a system of doors which open and shut to help the heart pump.
As the heart relaxes, two big veins are used blue into the right auricle and one big artoryiours fresh blood into the left auricle. Then the auricles begin to contract. This forces open a valve trapdoor in the floor of each auricle. The blood is pushed down into the ventricles with a "lub" sound.
Now the ventricles contract. The blood is pumped up with a sudden "dub" sound. On the right side it forces open a valve door loading to a huge vein which carries the used blood to the lungs. Here the blood filters through spongy tissues, giving up its carbon dioxide and taking on a fresh supply of oxygen, on the loft side, the contracting, ventricle forces upon a valve leading to the great aorta. This big artery divides and subdivides, sending fresh blcou to every part of the body.
The heart beats lub‑dub, lub‑dub about 70 times a minute. It beats day and night and in a normal life time it may beat lub‑dub two or three billion times. What's more, your little heart was happily beating away even before you were born.