Lesson 1
A cell shaped like a squished donut
Most cells are bumpy blobs. Red blood cells are different. They are round and flat, and pushed in on both sides, like a donut that forgot to make its hole.
That shape is a clever trick:
- More room for oxygen. The flat shape has lots of outside surface, so oxygen can get in and out fast.
- Super bendy. Some of your blood tubes are so tiny that red blood cells have to fold up to squeeze through in a single line.
- No nucleus! Grown-up red blood cells throw out their nucleus. That makes more space to carry oxygen.
Wow!
You have about 25 trillion red blood cells. That's more than any other kind of cell in your body!
Lesson 2
The great oxygen delivery
Every cell in your body needs oxygen to make energy. Without it, the power plants (mitochondria) stop working. Red blood cells make sure that never happens. Here is their trip:
- 1. Pick up. You breathe in. In your lungs, red blood cells grab oxygen from the air.
- 2. Pump. Your heart pushes the blood out through tubes called arteries.
- 3. Drop off. In your toes, brain, tummy, everywhere, the cells hand out oxygen.
- 4. Take out the trash. They help carry a waste gas called carbon dioxide back to your lungs, and you breathe it out.
The secret helper inside each red blood cell is called hemoglobin (HEE-muh-glow-bin). It grabs onto oxygen like a hand. Hemoglobin is also what makes your blood red!
Try this
Put two fingers on the side of your neck or on your wrist and feel your pulse. Each bump is your heart pushing red blood cells along. Count the bumps for 15 seconds, then multiply by 4. That's how many times your heart beats in a minute!
Wow!
A red blood cell can make a whole trip around your body in about one minute.
Lesson 3
Made inside your bones
Your bones are not just hard sticks. Inside the big ones is a soft, spongy stuff called bone marrow. It's a red blood cell factory!
Bone marrow makes about 2 million new red blood cells every second. It has to, because red blood cells wear out. All that squeezing through tiny tubes is hard work.
- A red blood cell lives for about 4 months (around 120 days).
- Old, worn-out cells get caught by your spleen and liver.
- Your body recycles the iron from old cells to build new ones. Nothing goes to waste!
Wow!
Since you started reading this lesson, your bones have made tens of millions of brand new red blood cells.
Lesson 4
Helping your red blood cells
To build hemoglobin, your body needs a metal called iron. Yes, there's a tiny bit of metal in your blood! You get iron from foods like:
- Beans, lentils, and peas
- Spinach and other dark green leaves
- Meat, chicken, fish, and eggs
- Some breakfast cereals that have iron added
When someone doesn't have enough red blood cells, it's called anemia (uh-NEE-mee-uh). Their body doesn't get enough oxygen, so they can feel tired, weak, or look pale. Doctors can check this with a blood test and help them feel better.
Try this
Run in place for 30 seconds, then notice your breathing and heartbeat. They speed up! Your muscles are asking for more oxygen, so your body sends more red blood cells their way.
Quiz
Red blood cell quiz