Blood Circulation: Trace a Heartbeat
Understand double circulation: blood passes through the heart twice on each complete lap, once to the lungs to pick up oxygen and once to the body to deliver it, with valves preventing backflow.
Before you try
What if the heart had only two chambers? Would oxygen-rich and oxygen-poor blood mix?
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What happened?
Move a control to see what changes and why.
One cell is followed around a simplified loop. Real blood moves billions of cells at once through a branching network.
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Try these ideas
- Press Step through the journey and read what happens at each station.
- Compare the litres pumped per minute at resting and running rates.
- Watch where the cells change colour and work out why it happens there.
Why it works
Human blood does a figure of eight. The right side of the heart takes oxygen-poor blood back from the body and sends it a short way to the lungs, where it drops carbon dioxide and picks up oxygen. The left side receives that fresh blood and pushes it all round the body. Because the left ventricle has the longer, harder job, its muscular wall is the thickest of the four chambers. Valves between the chambers snap shut so blood can only flow one way.
In this simulator blood cells travel a loop through the heart, the lungs and the body, changing from purple to red as they pick up oxygen. You can change the heart rate, read the litres pumped each minute and step through the eight stations one at a time to see what happens at each. Stroke volume is fixed at 70 mL here, whereas in a real body it also rises during exercise.
Check your understanding
Question 1 of 4
How many times does blood pass through the heart in one complete lap of the body?
Why is the wall of the left ventricle the thickest?
Where does blood pick up oxygen?
What is the job of the valves between the chambers?
Explain it in your own words
What changed? Why did it happen? Where might you notice this in everyday life?
For parents & teachers
- Find your pulse, count it at rest, then after skipping, and compare.
- Ask why athletes often have a lower resting heart rate.
- Discuss why a doctor listens to the heart with a stethoscope.