Double Circulation: Definition & Advantage

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  • 0:05 What is a Double…
  • 0:42 Some Basic Heart Anatomy
  • 2:12 How Does Blood Move…
  • 4:26 Lesson Summary
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Lesson Transcript
Laura Enzor

Laura has a Master's degree in Biology and is working on her PhD in Biology. She specializes in teaching Human Physiology at USC.

Expert Contributor
Amanda Robb

Amanda holds a Masters in Science from Tufts Medical School in Cellular and Molecular Physiology. She has taught high school Biology and Physics for 8 years.

Humans and many other organisms use a double circulatory system. This means that we have two separate circuits for blood in our body. Learn how these circuits differ and the function of each one.

What is a Double Circulation System?

The majority of mammals (including humans) utilize a double circulatory system. This means we have two loops in our body in which blood circulates. One is oxygenated, meaning oxygen rich, and the other is deoxygenated, which means it has little to no oxygen, but a lot of carbon dioxide.

Double circulatory systems are important because they ensure that we are giving our tissues and muscles blood full of oxygen, instead of a mixture of oxygenated and deoxygenated blood. While it may take a bit more energy than a single circulatory system, this system is much more efficient!

Some Basic Heart Anatomy

The organ that powers the circulatory system is the heart. The human heart pumps blood through four chambers: two atria and two ventricles. We also have four valves in our hearts that keep blood moving in one direction, preventing backflow back into the heart; two valves are found within the heart itself and two are found in the major arteries in the heart: the aorta and the pulmonary artery.

Humans have a 4-chambered heart (some organisms have only two or three chambers in their hearts; these animals are typically reptiles and fish), and we separate the heart into right and left halves. Each half of a human heart has one atrium, which sits 'on top' of one ventricle. The right and left halves of the heart are separated by a layer of muscle tissue called the septum. Keep in mind that when you look at a picture of a heart, it is shown how the heart would sit in your chest, so everything looks backwards.

There are two types of valves in the heart. The first set of valves are the atrioventricular valves that separate the atria from the ventricles. The tricuspid valve is the valve on the right side of the heart, and the bicuspid or mitral valve is the valve on the left side of the heart. The second set of valves are the semilunar valves that are found at the base of the aorta and the pulmonary artery. When you listen to your heart beat and you hear that 'lup-dub' sound, what you're hearing is the sound of these valves closing!

How Does Blood Move Through the Heart?

Let's start with the left side of the heart. Blood enters the left atrium, moves through the bicuspid, or mitral, valve, and into the left ventricle. Blood is then pushed through the aortic semilunar valve into the aorta. This blood is oxygenated and is distributed around the body, providing oxygen to our muscles and organs. Once this blood is deoxygenated, it returns to the heart through a few different veins.

Oxygenated blood moves through arteries, and deoxygenated blood moves through veins. Usually, these are shown on diagrams as red (oxygenated) and blue (deoxygenated). A simple way to remember this is that veins visit with deoxygenated blood, and arteries move away with oxygenated blood. The one big exception to this is the pulmonary artery. It carries deoxygenated blood!

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Additional Activities

A Walking Tour of the Heart

Students often struggle to envision how the blood is actually flowing through double circulation. This activity seeks to address this as students create a walking tour of the circulation. This activity will require red and blue sidewalk chalk and a large space to draw outside, as students will draw a body, the lungs, and a diagram of the heart in colored chalk. Deoxygenated parts of the circulation can be drawn in blue and oxygenated parts in red. Then, students will take themselves or a friend on a "walking" tour of the circulation and point out important structures that were taught in the lesson.


In this activity, you're going to act like a blood cell traveling through the double circulation of a human being. To create this "walking tour" you'll need red and blue sidewalk chalk and a large space to draw. Follow the directions below to draw out the circulation, then lead a friend on a walking tour through your work.

  1. Start by drawing a graphic heart in the center of your space.
  2. Divide the heart into four sections and label each of the different chambers of the heart. Use red for chambers that have oxygenated blood and blue for chambers that have deoxygenated blood.
  3. Next draw a set of lungs above the heart and a body below the heart.
  4. Next draw tubes that represent arteries and veins that connect the circulatory system. Make sure to use the correct colors for oxygenated and deoxygenated blood.
  5. Now that you have your circulation done, you can lead a friend on a walking tour of the circulation. Start in the body and flow back to the heart, then the lungs. Point out the important structures mentioned in the lesson as you go: right atrium, right ventricle, tricuspid valve, bicuspid valve, semilunar valves, left atrium and left ventricle.


  1. How did you represent red blood cells in double circulation?
  2. What could improve our model of double circulation? Were any components missing?

Expected Results

Students should be able to explain that they moved through the double circulation, just like red blood cells do. However, in this model, the red blood cells didn't actually "carry" oxygen or carbon dioxide, and this could be added in to make the model more accurate. Students might also report that their drawing could be more scientifically accurate.

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