Your heart is a strong, steady pump about the size of your fist. It pushes blood through tubes called blood vessels to every part of your body. The blood carries oxygen and nutrients your cells need to work and grow. When you run or climb stairs, your heart beats faster to deliver more oxygen. Resting helps it slow down again so the body can save energy.
Comprehension Check
What is the main job of the heart?
Why does your heart beat faster during exercise?
The Lungs at Work
Your lungs fill with air each time you breathe in. Tiny air sacs inside them pass oxygen into your blood and remove carbon dioxide, a waste gas. Breathing through your nose can warm and filter the air. When you blow up a balloon or sing a long note, your lungs and the muscles between your ribs work together to push air out in a steady stream.
Comprehension Check
What happens in the tiny air sacs of the lungs?
Which habit helps clean the air before it reaches your lungs?
Bones and Muscles Team Up
Bones give your body shape and protect organs like your brain and heart. Muscles attach to bones and pull on them to help you move. Joints are places where bones meet and bend, like your knees and elbows. To keep bones strong, eat foods with calcium and stay active. Stretching before sports helps muscles work safely and prevents injuries.
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