Body Systems - 7th Grade: Circulatory System

• Put your hand on your heart. Did you place your hand on the left side of your chest? Many people do, but the heart is actually located almost in the center of the chest, between the lungs. It's tipped slightly so that a part of it sticks out and taps against the left side of the chest, which is what makes it seem as though it is located there.
  
  
• Hold out your hand and make a fist. If you're a kid, your heart is about the same size as your fist, and if you're an adult, it's about the same size as two fists.
  
  
• Your heart beats about 100,000 times in one day and about 35 million times in a year. During an average lifetime, the human heart will beat more than 2.5 billion times.
  
  
• Give a tennis ball a good, hard squeeze. You're using about the same amount of force your heart uses to pump blood out to the body. Even at rest, the muscles of the heart work hard—twice as hard as the leg muscles of a person sprinting.
  
  
• Feel your pulse by placing two fingers at pulse points on your neck or wrists. The pulse you feel is blood stopping and starting as it moves through your arteries. As a kid, your resting pulse might range from 90 to 120 beats per minute. As an adult, your pulse rate slows to an average of 72 beats per minute.
  
  
• The aorta, the largest artery in the body, is almost the diameter of a garden hose. Capillaries, on the other hand, are so small that it takes ten of them to equal the thickness of a human hair.
  
  
• Your body has about 5.6 liters (6 quarts) of blood. This 5.6 liters of blood circulates through the body three times every minute. In one day, the blood travels a total of 19,000 km (12,000 miles)—that's four times the distance across the US from coast to coast.
  
  
• The heart pumps about 1 million barrels of blood during an average lifetime—that's enough to fill more than 3 super tankers.
  
  
• lub-DUB, lub-DUB, lub-DUB. Sound familiar? If you listen to your heart beat, you'll hear two sounds. These "lub" and "DUB" sounds are made by the heart valves as they open and close. See the valves in action.
  
  

Circulatory System