Circulation & Breathing Together
Understand how the circulatory and respiratory systems work together: the lungs oxygenate the blood, the heart pumps it around the body, cells use the oxygen and produce carbon dioxide waste, and the blood carries the waste back to the lungs to be breathed out
What a learner can do afterwards
- Describe the cycle: lungs add oxygen to blood → heart pumps oxygenated blood to body → cells use oxygen → blood returns carbon dioxide to lungs
- Explain why heart rate and breathing rate increase during exercise (muscles need more oxygen)
- Measure their own resting and post-exercise heart rate and explain the difference
1 · Read
When you run, your leg muscles need more oxygen to keep going. Your respiratory system and your circulatory system work as one team to deliver it. Air reaches your lungs, and oxygen passes into the blood there. Your heart pumps that oxygen-rich blood out to cells all over your body. The cells use the oxygen and make carbon dioxide waste, and the blood carries that waste back to the lungs to be breathed out.
Zara starts jogging. Her leg muscles burn fuel fast and need more oxygen. Her heart pumps faster to rush oxygen-rich blood to those muscles, and her lungs breathe faster to bring in more oxygen and clear out the extra carbon dioxide.
When your muscles work harder, they use up oxygen faster and make more carbon dioxide waste. That is why your heart rate and your breathing rate climb together during exercise, not just one of them.
Lungs, heart, and cells work as one team: oxygen goes in, carbon dioxide goes out, and exercise speeds up the whole cycle.
The rewritten readings were written for this dataset.
More to read
How lungs and blood work together
Breathing and circulation share a job. Air enters through your mouth or nose and travels along the trachea to your lungs. There, oxygen crosses from tiny air sacs into blood. These parts belong to the respiratory system.
Your heart pumps blood along blood vessels. Together, they form the circulatory system. Blood delivers oxygen throughout your body. Most body cells need it to release energy from food. They produce carbon dioxide, a waste gas that blood returns to the lungs for you to breathe out.
The lungs exchange the gases. The heart and vessels keep blood moving between the lungs and the rest of your body. This cycle continues while you are awake and while you sleep.
Following air into your lungs
Your respiratory system brings oxygen into blood and removes carbon dioxide made by your cells. Blood carries the gases between your lungs and body.
Air can enter your mouth or nose. Your nose adds warmth and moisture. Its hairs and mucus help catch dust and germs, though they cannot catch everything. Air then passes through the trachea, a firm tube in your throat that divides into a branch for each lung.
Within each lung, more branches form ever smaller tubes. Millions of air sacs called alveoli sit at their ends. Thin blood vessels surround these sacs.
Across the thin walls, oxygen moves into blood as carbon dioxide moves into the sacs. You breathe the carbon dioxide out. This swap is called gas exchange. It takes place as you breathe.
The jobs of blood's different parts
Blood contains several parts with different tasks.
Inside red blood cells, a protein named hemoglobin binds oxygen in the lungs. As blood reaches tissues needing oxygen, the protein releases it. Hemoglobin also carries part of the carbon dioxide travelling back to the lungs.
White blood cells help defend you by fighting germs.
Platelets are small cell fragments. They collect where a blood vessel is damaged and help make a clot that stops bleeding.
A pale yellow fluid called plasma carries the blood cells and platelets. Most of plasma is water. It also transports nutrients from food. Together, these parts carry oxygen and nutrients to tissues and take wastes away.
Blood's oxygen round trip
Blood connects your lungs with tissues throughout your body. Oxygen first crosses the walls of the lung's air sacs. Most binds to hemoglobin inside red blood cells for transport.
Your heart sends this oxygen-rich blood to the tissues. Hemoglobin releases oxygen where it is needed, including muscles working during a run. Cells use the oxygen to get energy from food.
Carbon dioxide made by those cells enters the blood for the return journey. At the lungs, it moves into the air sacs and leaves when you breathe out. Blood takes up oxygen again, ready for another circuit.
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