Blood and Circulation
Every minute of every day, your heart is working tirelessly to keep you alive. The sheer amount of pumping it does is truly astonishing. Let us find out exactly how much traffic is moving through your body's personal transport system!
How Much Work Does Your Heart Actually Do?
Over once a second, every single day! Bill Nye the Science Guy shows us that your heart never takes a break. It is a powerful muscle that continually pumps blood, beating around 100,000 times a day just to keep your body functioning.
Thousands of litres! Even though you only have about 5 litres of blood inside you, your heart works so efficiently that it recirculates that same blood over and over, effectively pumping thousands of litres through your blood vessels every 24 hours.
Put Your Instincts to the Test
Think about what you already know about your body. Pick an answer for each question, then see if your instincts were right.
Arteries! Remember what Bill Nye the Science Guy says: "A" is for Arteries, and "A" is for Away. They carry oxygen-rich blood out to the rest of your body through strong, thick walls.
To fight off sickness and disease! White blood cells act like your body's personal security team. They travel through your circulatory system, hunting down viruses and bacteria to keep you healthy.
5 litres! In the episode, Bill Nye the Science Guy demonstrates this volume. It is roughly equivalent to two and a half large, two-litre bottles of soda moving through your body right now.
Understanding the Science
Tap each card to uncover the incredible components that make up your blood and the highway system it travels on.
Key Concepts
Red Blood Cells
Tap to learn moreThese are the delivery trucks of your circulatory system. They carry oxygen from your lungs to every single tissue and muscle in your body, and they pick up waste carbon dioxide to carry back to the lungs.
White Blood Cells
Tap to learn moreThis is your body's defence force. As Bill Nye the Science Guy demonstrates, these cells patrol your bloodstream looking for invaders, fighting off infections and diseases to keep you well.
Platelets
Tap to learn morePlatelets are tiny cell fragments that stick together to form complex nets and clots. They are essential for stopping you from bleeding when you get a scrape or cut.
Plasma
Tap to learn moreThis is the liquid component of your blood. Plasma is actually a yellowish colour! It acts as the river that carries all the red cells, white cells, platelets, and nutrients around your body.
Arteries
Tap to learn moreThese are the strong, thick-walled blood vessels that carry oxygen-rich blood away from your heart and distribute it to the rest of your body under high pressure.
Veins
Tap to learn moreOnce your cells have dropped off their oxygen, veins act as the return highway. They carry the darker, deoxygenated blood back to the heart so it can be sent to the lungs for a fresh supply.
Capillaries
Tap to learn moreThese are the microscopic bridges connecting arteries to veins. Capillaries have walls so thin that oxygen, nutrients, and carbon dioxide can easily pass right through them into your tissues.
The Heart Chambers
Tap to learn moreYour heart is divided into four distinct rooms called chambers. The top two are the atria, and the bottom two are the ventricles. They squeeze in perfect coordination to keep your blood flowing smoothly.
Try It: The Capillary Exchange Mission
Your leg muscle is working hard! Empty red blood cells are flowing into your lungs. You have two jobs to keep the muscle energised:
1. In the Lungs (Left): Tap the floating Oxygen (O2) molecules to load them onto passing empty cells.
2. In the Muscle (Right): Tap the bright red, loaded cells to drop off the O2 into the muscle and swap it for CO2 waste!
Science Fact: Fortunately for us, this two-way exchange happens entirely automatically through a process called passive diffusion. It is all part of a larger biological mechanism known as homeostasis, which keeps our body perfectly in balance. When you exercise, your body automatically alters your heart rate to ensure your muscles get exactly as much oxygen as they need while rapidly removing waste carbon dioxide!
Apply Your Knowledge
Let us see if you can connect the microscopic components of your circulatory system to their vital jobs.
Match the Concepts
Click an object to select it, then click the matching description to place it.
Real-World Challenge
Imagine you have just run a very fast race. Your muscles need a lot more oxygen than usual. Based on what you have learned about the circulatory system and homeostasis, describe the chain of events that happens in your body to get that extra oxygen down to your legs and remove the extra carbon dioxide.
What Has Changed Since This Episode Aired
This episode first aired in 1994. While the core science of the circulatory system remains completely accurate, our understanding of some details has been refined.
Updated: We now emphasise in modern biology that human blood is never actually blue. Deoxygenated blood is simply a darker, deeper shade of red. Veins only appear blue through our skin because of how human tissue scatters and absorbs different wavelengths of light. It is an optical illusion!
Updated: While a plug is correct, modern science has mapped out exactly how this happens through a complex process called the "coagulation cascade". We now know it involves over a dozen different chemical clotting factors working together like a molecular domino effect to build a sturdy net over a wound.
Test Your Understanding
Answer these questions and get instant feedback. How many can you get right?
Results
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Reflection
If you could shrink down to the size of a red blood cell and travel through your own circulatory system, what part of the journey do you think would be the most exciting to see? Why?
Episode Discussion
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