Circulation Station


Put your fingers on your wrist. Feel something throbbing just below the surface of your skin? It’s your pulse, letting you know that your heart is working hard. Each time your heart beats, it pumps blood along a network of tubes called blood vessels. This network, along with your heart, is known as the circulatory system, and it reaches every cell in your body. Your blood travels in a never-ending cycle, delivering supplies and taking away wastes. Within your blood, red blood cells have a specialized task. They pick up oxygen in your lungs and carry it to your body’s tissues and organs. Your blood then transports carbon dioxide back to the lungs where you can breathe it out.

The Body’s Superhighway


Welcome to the hardest working muscle in your body. Your heart powers the circulatory system. Think of your heart as two pumps, working side by side. One pump receives oxygen-poor blood from your body and pushes it next door to your lungs where it picks up oxygen. The other pump receives oxygen-rich blood back from your lungs and gives it a boost out to your body.


Your lungs are specially equipped to do a very important job. Take a deep breath. Your spongy lungs have just filled with air and allowed oxygen to pass into your blood. Now breathe out. Your lungs have worked again—this time letting gasses you don’t need, like carbon dioxide, pass from your blood back out into the air.


Your arteries (ar-tuh-reez) are blood vessels that carry oxygen-rich blood from your heart out to the rest of your body. These muscular tubes have thick strong walls to handle the high pressure of freshly pumped blood. In illustrations arteries are usually colored red because the blood inside of them is bright red—a sign that red blood cells are carrying lots of oxygen.


Your capillaries (cap-ill-air-ies) are tiny blood vessels that distribute blood from your arteries (ar-tuh-reez) to the billions of cells in your body, and then to your veins (vayns). The walls of capillaries are very thin—so thin that nutrients and oxygen can pass right through them. As red blood cells pass through the capillaries, they drop off the oxygen that your cells need to live, and pick up the waste gas, carbon dioxide.


Veins (vayns) are blood vessels that carry your oxygen-poor blood back to the heart. This is a pretty difficult job. When blood flows to your toes, it’s a downhill ride. Getting the blood back up to your heart is a little harder. The veins in your arms and legs have little flap-like valves that help prevent blood from flowing backwards.

Complete the Loop

Around and Around We Go
Your blood circulates around your body more than a thousand times a day.
Imagine for a moment that you are a red blood cell. See if you can complete the tasks below.

Task: You are a red blood cell and have just arrived at the heart. Where do you go to pick up oxygen?

Task: You are in the lungs and have just loaded up with oxygen. Where do you go next?

Task: The heart is ready to pump you out to tissues and organs that need the oxygen you are carrying. Do you travel through an artery or vein?

Task: You need to deliver oxygen to the organ that does your thinking. Where do you go?

Task: You have delivered oxygen to the brain and have picked up the waste gas, carbon dioxide. You are ready to drop off your carbon dioxide and pick up some more fresh oxygen. Do you travel through an artery or vein?

A Doctor Making a Difference

Helen Brooke Taussig was a frail child who suffered from the learning problem, dyslexia (dis-lex-ee-uh). When she grew older, she also lost her hearing. Nevertheless, she beat the odds to become a doctor and make an important medical discovery. Dr. Taussig worked with “blue babies,” whose color at birth indicated that they were not getting enough oxygen. Some of these babies died immediately. Others only lived a few years.

Dr. Taussig discovered that these babies had poor blood flow between their hearts and lungs. She worked with Dr. Alfred Blalock and his brilliant technician, Vivien Thomas, and developed a new heart operation for “blue babies.” In 1944 they had their first success. Since then, the lives of many children have been saved.

Red arrow surrounded by a red circle pointing to the top of the page  Back to top