Heart and Blood

Core Idea

Your heart is a muscle in your chest that pumps blood through your body all day and all night. Blood travels through tubes called blood vessels to every part of you. Blood carries oxygen from your lungs and nutrients from your food to all your body parts, and it carries waste away.

How It's Best Learned

Feel your heartbeat by placing your hand on your chest. Find your pulse on your wrist. Jump up and down for 30 seconds and notice how your heart beats faster. Talk about why your heart speeds up when you exercise.

Common Misconceptions

• Children may think their heart looks like a Valentine's heart shape (the real heart looks more like a fist).
• Some children think blood is blue in veins and red in arteries (blood is always red, just different shades).
• Children may not realize the heart is a muscle that never rests.

Explainer

Put your hand on the left side of your chest. Can you feel it? That steady thump-thump is your heart beating. Your heart is a muscle about the size of your fist, and its job is to pump blood through your entire body. It beats about 100,000 times every single day — and it never stops, not even when you sleep.

Blood is a red liquid that flows through a network of tubes called blood vessels. These vessels reach every part of you — from the top of your head to the tips of your toes. If you could stretch out all your blood vessels in a line, they would wrap around the Earth more than twice! Blood vessels come in different sizes: big ones near your heart and tiny ones (thinner than a hair) reaching into your fingers and toes.

Blood is like a delivery truck for your body. When blood passes through your lungs, it picks up oxygen — the gas you breathe in. Then your heart pumps this oxygen-rich blood out to your muscles, brain, skin, and organs. Your body parts use the oxygen for energy. The blood also picks up nutrients from the food you digest and delivers those too. On the way back, blood picks up waste that your body does not need and carries it to your lungs (where you breathe out carbon dioxide) and your kidneys (which filter out other waste).

Why does your heart beat faster when you run or play? Because your muscles are working hard and need more oxygen and energy. Your heart speeds up to pump blood faster, delivering supplies more quickly. When you rest, your muscles calm down and your heart slows back to its normal pace. Your heart always adjusts to match what your body needs — faster during exercise, slower during rest, steady while you sleep.