Abstract
You know when you’re racing really fast—so fast that your heart is pounding, and you can’t catch your breath? Have you ever wondered why that happens? Imagine you are racing—when you take a deep breath, you breathe in air and your lungs pull oxygen into your blood, then oxygen races to your hungry leg muscles. All that work by your muscles to make energy creates carbon dioxide waste, which travels back to the lungs, and we exhale with a sigh of relief. As you and your muscles work harder to run faster and further, your muscles require more oxygen to make more energy. Over time, with continued exercise, your heart and lungs respond by becoming more efficient at delivering oxygen and making energy. There are even ways to measure how hard your body is working during exercise, and this article will tell you how!
Highlights
You know when you’re racing really fast—so fast that your heart is pounding, and you can’t catch your breath? Have you ever wondered why that happens? Imagine you are racing—when you take a deep breath, you breathe in air and your lungs pull oxygen into your blood, oxygen races to your hungry leg muscles
All that work by your muscles to make energy creates carbon dioxide waste, which travels back to the lungs, and we exhale with a sigh of relief
Oxygen-containing blood is pumped by the heart through the blood vessels to the muscles, where it can be used by mitochondria to make energy from sugar
Summary
A protein in red blood cells that can carry four oxygen molecules. lungs. A protein in red blood cells that can carry four oxygen molecules. All the alveoli together have a surface area about the size of a tennis court, which makes the lungs very e cient at pulling out oxygen from air (Figure ). Hemoglobin, the protein in red blood cells that makes them look red, has a high attraction for oxygen and can carry four oxygen molecules at a time. The blood cells are ready to race back to the heart through blood vessels! The heart is responsible for receiving oxygen-rich blood from the lungs and pumping it out to all the organs, like the brain, stomach, and skeletal muscles. A protein in muscle cells that can take oxygen from hemoglobin
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