The human body likes to be in a balance. For example, if you are hungry then you will eat to stop the hunger. The circulatory system is important because it also helps the body maintain balance. The circulatory systemís job is to transport oxygen and nutrients to the cells throughout the body and to get rid of waste materials such as carbon dioxide. This system consists of the heart, blood vessels, and blood.
Now, think of your blood vessels as being the bus routes that your bus takes every morning to school and back home. Some of these routes will go on main roads, which have two or more lanes. Other roads will be smaller with just one lane like the streets that you live on. Just like the roads, because of its sizes the arteries and veins are like the main roads and the capillaries are like the small streets.
Next, imagine that each bus is the individual blood that takes you from one place to the other. Think of your blood as being the different bus that different students take because of where he or she lives. Unlike the buses, the blood can make trillions of stops in only 30 seconds. The blood never leaves your body because it keeps being re-used by the body. The only time it leaves the body is when you cut yourself or when the nurse draws out your blood to be examined. For this reason, the circulatory system in humans is referred to as a closed system.
Finally, the heart is like the bus headquarters. It is the central location that tells the blood which route and direction to flow in. The heart is the pump that puts pressure on the blood allowing it to flow to the different cells in the body. Throughout the average human life, the heart will contract (beat) about 3 billion times. It will only stop for about a fraction of a second between beats!
Other Interesting Sites
1. Find a Heartbeat
2. Picture of a Real Heart
3. Circulatory System Movie Clip
4. Listen to Different Beats
5. What is the Circulatory System?
6. Blood Flow Cycle
7. Virtual Body Tour