Circulatory (blood) system
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Bernard Nebel.
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The heart is the main organ of the circulatory system. However, please don’t get hung up on details of the heart. Rather, keep kid’s focus on the fact that the basic role of the circulatory (blood) system is to transport nutrients within body from places of entry to where they are used—always the countless individual cells of the body—and wastes from where the are produced—again all the individual cells of the body—to points of exit. (Use the above as examples.)
The real business part of the circulatory system is the millions of capillary beds that permeate every organ and tissue. It is at, and only at, the capillary beds that things actually enter or leave the blood stream. Here is a micro-photo video of blood flowing through capillaries.
Type into your browser: capillary beds images for further illustrations of capillary beds. Have kids note that all capillary beds are connecting pathways between arteries coming from the heart and veins going back to the heart. The capillary beds assure that all cells of the body are in close contact with the blood to receive nutrients and dispose of wastes. The following video illustrates these points:
The main organ of the circulatory system is of course the heart, which keeps the blood flowing on its continuous circuit from heart through arteries to capillary beds in all parts of the body and from each capillary bed through veins back to the heart. The following video describes heart function. You can ignore the complex terminology but help kids analyze how the valves and the contractions of the heart muscle keep blood flowing in a single direction. Have kids note how the heart is really two pumps in one. One pumping blood through the lungs; the other pumping blood to all other parts of the body, through capillary beds back to the heart. The course of blood circulation thus follows a figure eight pattern.
Discuss how having blood go through the lungs on every circuit speaks to the significance energy metabolism in keeping the body functioning.
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