# What is blood made of?

An episode of [Science for Kids / Science's Not Boring: The Kids Science Podcast](https://invisiblenetwork.ai/podcast/1896928296), 13 Aug 2026, 11 min.

Audio: https://www.buzzsprout.com/2624612/episodes/19607630-what-is-blood-made-of.mp3

Have you ever scraped your knee and wondered, what is blood actually made of? It is not just red water—it is a microscopic superhero team living inside you! Join Mira and Finn as they shrink down and race through your veins on a 60,000-mile biological superhighway! Did you know your blood vessels are long enough to wrap around the entire Earth twice? Discover the amazing secrets of your body, from millions of squishy red blood cells delivering oxygen, to shape-shifting white blood cells called macrophages that eat dangerous germs whole! Learn how sticky platelets weave superglue nets to plug leaks just like a submarine hatch. You will also find out about the Dutch scientist who first spotted these tiny cells in 1674, and even travel the animal kingdom to uncover bizarre creatures with bright blue and neon green blood! Get ready for a mind-blowing journey inside the human body that proves science is definitely not boring!

## Transcript

[0:00] SPEAKER_00: Welcome to Science Is Not Boring by Kidopoly.com.
[0:04] SPEAKER_00: I'm Mira! And I'm Finn! Today we're zooming inside the human body to explore something that keeps you alive every single second of every single day.
[0:15] SPEAKER_01: Wait, is it an alien parasite?
[0:17] SPEAKER_01: Please tell me it's not an alien parasite.
[0:20] SPEAKER_00: No! It's blood! Give yourself a little scratch, and out comes something red and warm.
[0:27] SPEAKER_00: But blood isn't just red water, it is actually a microscopic superhighway.
[0:32] SPEAKER_00: And here is a mind-blowing fact to start us off.
[0:36] SPEAKER_00: Ooh, lay it on me! If you took all the blood vessels, which are the tubes carrying blood, out of an adult's body and laid them end to end, they would stretch for about 60,000 miles.
[0:52] SPEAKER_00: How far is that exactly?
[0:54] SPEAKER_00: That is long enough to wrap around the entire Earth over two whole times.
[0:58] SPEAKER_00: And you have all that packed inside you right now.
[1:02] SPEAKER_00: Inside me?
[1:03] SPEAKER_00: But I'm only four feet tall.
[1:05] SPEAKER_00: How does that even fit?
[1:07] SPEAKER_00: Most of them are totally microscopic.
[1:09] SPEAKER_00: Today we are going to shrink down and journey through your veins to find out what blood is really made of, how it races around this giant track, and how it magically mends its own leaks.
[1:21] SPEAKER_01: Okay, so if I scrape my elbow, I see red liquid.
[1:25] SPEAKER_00: And it usually feels kind of warm, right?
[1:28] SPEAKER_00: Exactly.
[1:29] SPEAKER_00: Blood deep inside your body is actually a toasty 98.6 degrees Fahrenheit, which is your normal body temperature.
[1:37] SPEAKER_00: But it's not just red water.
[1:40] SPEAKER_00: Then what is it made of?
[1:42] SPEAKER_00: Over half of your blood, about 55%, is a yellowish liquid called plasma.
[1:48] SPEAKER_00: Plasma is 90% water, mixed up with salts, sugars, and proteins.
[1:54] SPEAKER_00: Wait, if over half my blood is yellow liquid, why does it look bright red?
[1:59] SPEAKER_00: Because of the red blood cells! A single drop of blood, the size of a pinhead, holds about 5 million red blood cells.
[2:08] SPEAKER_00: They completely overpower the yellow colour.
[2:11] SPEAKER_00: Five million in one tiny drop?
[2:14] SPEAKER_00: What do they look like if you zoom in?
[2:16] SPEAKER_00: Imagine millions of tiny, squishy red donuts, but the hole in the middle isn't punched all the way through.
[2:23] SPEAKER_00: Who even figured that out?
[2:25] SPEAKER_00: You can't just see them with your eyeballs.
[2:27] SPEAKER_00: You're right.
[2:28] SPEAKER_00: Back in 1674, a Dutch fabric merchant named Anthony van Leeuwenhoek made his own supermagnifying glass lenses.
[2:37] SPEAKER_00: He pricked his finger, looked at his blood, and became the first person to accurately describe human red blood cells.
[2:44] SPEAKER_01: That is so brave.
[2:46] SPEAKER_01: Sticking your own finger just to see what's inside.
[2:49] SPEAKER_00: He wrote that he saw tiny round particles floating in a clear liquid.
[2:54] SPEAKER_00: He was looking at the body's ultimate delivery fleet, and he didn't even know the full story yet.
[2:59] SPEAKER_00: So if they are a delivery fleet, what are these squishy red donuts delivering on the superhighway?
[3:05] SPEAKER_00: Oxygen! Every time you breathe in, red blood cells grab oxygen from your lungs and race to deliver it to every single corner of your body, from your brain down to your little toe.
[3:17] SPEAKER_01: How fast do they drive on this 60,000 mile highway?
[3:21] SPEAKER_00: Super fast.
[3:23] SPEAKER_00: One red blood cell can zip through your whole body and make it all the way back to your heart in just 20 to 60 seconds.
[3:31] SPEAKER_00: That's like a roller coaster.
[3:33] SPEAKER_00: But what pushes them so fast?
[3:35] SPEAKER_00: Do they have tiny engines?
[3:37] SPEAKER_00: Your heart is the engine.
[3:40] SPEAKER_00: It's a powerful muscle that beats about a hundred thousand times a day.
[3:44] SPEAKER_00: It pumps 2,000 gallons of blood every single day.
[3:50] SPEAKER_00: 2,000 gallons?
[3:51] SPEAKER_00: That's enough to fill a giant tanker truck.
[3:54] SPEAKER_00: But wait, how do they fit into my toes?
[3:57] SPEAKER_00: To reach every cell, the blood vessels get smaller and smaller.
[4:01] SPEAKER_00: The smallest tubes, called capillaries, are only 8 micrometers wide.
[4:07] SPEAKER_00: How small is 8 micrometers?
[4:10] SPEAKER_00: That is about one-tenth the thickness of a single human hair.
[4:14] SPEAKER_00: The red blood cells literally have to fold themselves in half just to squeeze through in a single file line.
[4:21] SPEAKER_00: That sounds exhausting.
[4:23] SPEAKER_00: Squeezing and racing all day long.
[4:25] SPEAKER_00: Do they ever wear out?
[4:27] SPEAKER_00: They do.
[4:28] SPEAKER_00: Because they work so hard, a red blood cell only lives for about 120 days.
[4:34] SPEAKER_00: But your bone marrow, the squishy inside of your bones, pumps out two million brand new red blood cells every single second to replace them.
[4:45] SPEAKER_00: 2 million new cells a second?
[4:48] SPEAKER_01: My bones are working overtime! But hey, if the blood is always racing around under high pressure, why doesn't it all just spray out when I get a cut?
[4:57] SPEAKER_00: That is where your biological repair crew comes in.
[5:00] SPEAKER_00: They are called platelets and they look like tiny spiky plates.
[5:04] SPEAKER_00: Spiky plates?
[5:06] SPEAKER_00: Are they dangerous?
[5:07] SPEAKER_00: Only to the leek.
[5:09] SPEAKER_00: The second a blood vessel tears, platelets rush to the scene.
[5:13] SPEAKER_00: Within seconds, they stick to the edges of the cut and to each other, acting like sticky biological superglue to plug the hole.
[5:21] SPEAKER_00: Oh, it's like throwing a giant net over a leak in a submarine.
[5:25] SPEAKER_00: Literally, they weave a net of sticky protein threads called fibrin.
[5:30] SPEAKER_00: It traps the passing red blood cells to form a clump, which eventually dries into a hard scab on your skin.
[5:36] SPEAKER_00: Okay, that fixes the leak.
[5:38] SPEAKER_01: But what if nasty dirt and germs sneak in before the submarine hatch closes?
[5:43] SPEAKER_00: Then your body calls in the heavy artillery, the white blood cells.
[5:47] SPEAKER_00: You have about 4,500 to 11,000 of them in every drop of blood, constantly patrolling for invaders.
[5:55] SPEAKER_00: Are they like tiny knights with microscopic swords?
[5:58] SPEAKER_00: Even wilder! They are shape-shifting warriors.
[6:02] SPEAKER_00: One famous type is the macrophage, which literally means big eater.
[6:08] SPEAKER_00: Wait, it eats the germs?
[6:10] SPEAKER_00: Yes.
[6:11] SPEAKER_00: When a macrophage spots a bacteria, it crawls after it, stretches out gooey arms called pseudopods, and swallows the germ whole, dissolving it completely.
[6:21] SPEAKER_01: That is incredible! I have oxygen delivery trucks, sticky submarine pluggers, and shape-shifting germ eaters inside me right now.
[6:29] SPEAKER_00: Exactly! And blood is so complicated that it took a long time for doctors to fully understand it.
[6:36] SPEAKER_00: In the year 1900, a scientist named Carl Landsteiner mixed different people's blood in a lab and noticed it sometimes clumped up.
[6:45] SPEAKER_00: Why did it clump up?
[6:47] SPEAKER_00: Did he break it?
[6:48] SPEAKER_00: No, he discovered that humans have different main blood types, like A, B, and O.
[6:54] SPEAKER_00: They don't all mix safely.
[6:55] SPEAKER_00: He won the Nobel Prize in 1930 because his discovery means doctors now know exactly how to safely give sick people extra blood.
[7:04] SPEAKER_01: Wow, that one discovery probably saved millions of lives.
[7:08] SPEAKER_01: Okay, humans have red blood.
[7:11] SPEAKER_01: But do any animals have weird, alien-coloured blood?
[7:14] SPEAKER_00: Yes, the amazing horseshoe crab has bright blue blood.
[7:18] SPEAKER_00: It uses a chemical with copper inside to carry oxygen instead of iron.
[7:23] SPEAKER_01: Haha, bright blue blood! Are there any other crazy colours?
[7:28] SPEAKER_00: In New Guinea there is a lizard called the green-blooded skink.
[7:31] SPEAKER_00: Its blood is packed with a green chemical so strong that its bones, muscles, and even its tongue are neon green.
[7:38] SPEAKER_00: Neon green blood, bones and tongue?
[7:41] SPEAKER_00: Nature is the coolest thing ever.
[7:43] SPEAKER_00: Alright Finn, time for the quiz.
[7:45] SPEAKER_01: Are you ready?
[7:47] SPEAKER_01: Okay, my brain is warmed up.
[7:49] SPEAKER_01: Hit me with the questions.
[7:50] SPEAKER_00: First question.
[7:52] SPEAKER_00: What is the total length of the blood vessels in an adult's body?
[7:59] SPEAKER_00: Next one.
[8:01] SPEAKER_00: Who was the Dutch fabric merchant that first accurately described human red blood cells in 1674?
[8:12] SPEAKER_00: Question 3.
[8:14] SPEAKER_00: How many red blood cells are packed into a single pinhead-sized drop of blood?
[8:23] SPEAKER_00: Here's number four.
[8:25] SPEAKER_00: What are the tiny spiky cells that act like biological superglue to heal your cuts?
[8:34] SPEAKER_00: Last question.
[8:36] SPEAKER_00: What bizarre animal in New Guinea has neon green blood, bones and muscles?
[8:45] SPEAKER_00: Great job! Let's see how you did.
[8:48] SPEAKER_00: Let's go through the answers.
[8:50] SPEAKER_00: The first answer is the blood vessels would stretch for about 60,000 miles, enough to wrap around the Earth over two times.
[9:00] SPEAKER_00: For question two, it was untony Van Leeuwenhoek.
[9:04] SPEAKER_00: Number three, the answer is there are about five million red blood cells in a single drop.
[9:11] SPEAKER_00: Question four.
[9:13] SPEAKER_00: The sticky, spiky repair cells are called platelets.
[9:17] SPEAKER_00: And the final answer is the green blooded skink.
[9:21] SPEAKER_01: I am never going to look at a scraped knee the same way again.
[9:25] SPEAKER_01: Knowing all those cells are rushing to build a sticky submarine net is just awesome.
[9:32] SPEAKER_00: Right?
[9:33] SPEAKER_00: And just think of those macrophage big eaters gobbling up the germs.
[9:37] SPEAKER_00: Your body is a microscopic superhero team.
[9:40] SPEAKER_01: If you think macrophages and neon green lizard blood are as awesome as we do, please leave us a five-star review.
[9:47] SPEAKER_00: Yes! Just scroll down on your podcast app and tap those five stars.
[9:52] SPEAKER_00: It really helps us out.
[9:54] SPEAKER_00: Oh, and don't forget to check out our site, kidopoly.com.
[9:58] SPEAKER_00: We've got tons of fun learning games and cool science activities there.
[10:03] SPEAKER_00: And if you want a shout out on the show, or just want to tell us your favourite weird science fact, email us at hello at kidopoly.com.
[10:12] SPEAKER_00: Keep asking questions and exploring the incredible world around you.
[10:16] SPEAKER_00: See you next time on Science Is Not Boring.
[10:20] SPEAKER_00: Bye everyone!

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