Human Circulatory System
Primary 6 · Science and Elementary Technology
Human Circulatory System
Lesson 2 of 6
30 min
Let's begin
Make a fist with your hand. Your heart is about that size. It sits in the middle of your chest, tilted slightly to the left, safely protected by your ribs. It started beating before you were born, and it has never stopped for a rest. How can it keep working like that? Let us look inside.
The heart is made of cardiac muscle, a special muscle found only in the heart. It squeezes and relaxes again and again without getting tired. Each squeeze pushes blood out into the blood vessels.
The heart has four hollow spaces called chambers:
The right side of the heart (right atrium and right ventricle) deals with blood that has little oxygen, coming from the body and going to the lungs. The left side (left atrium and left ventricle) deals with oxygen-rich blood, coming from the lungs and going to the body.
A thick wall called the septum divides the left side from the right side. It keeps oxygen-rich blood and oxygen-poor blood from mixing.
Valves are flaps that work like one-way doors. They are found between each atrium and ventricle, and where the blood leaves the ventricles. They let blood flow forward and stop it from flowing backwards. The "lub-dub" sound of your heartbeat is made by the valves snapping shut.
The ventricles have thicker walls than the atria, because they must push blood much further. The left ventricle has the thickest wall of all, because it pumps blood to the whole body; the right ventricle only pumps blood next door, to the lungs.
| Blood vessel | Where it carries blood |
|---|---|
| Vena cava (superior and inferior) | From the body into the right atrium |
| Pulmonary artery | From the right ventricle to the lungs |
| Pulmonary veins | From the lungs into the left atrium |
| Aorta, the biggest artery | From the left ventricle to the whole body |
Draw a large outline of the heart and divide it into four chambers with a thick septum down the middle. Label the right atrium and right ventricle on the left of your page (because you are facing the person), and the left atrium and left ventricle on the right. Make the left ventricle wall the thickest. Add the valves, the vena cava, the pulmonary artery, the pulmonary veins and the aorta. Colour oxygen-poor blood blue and oxygen-rich blood red.
Tip
Atria are the upstairs rooms, where blood arrives; ventricles are downstairs, where the heavy pushing is done. The Left ventricle is the strongest because it Launches blood to the whole body.
Answers
What you learned today
Sources and credits
The exercises (Try it yourself and the practice questions) are written by Ganzaa.
This lesson adapts CC BY-SA material and is shared under CC BY-SA 4.0.
Quick check
Which chamber of the heart has the thickest wall?
