You are listening to Sleep Tight Science.
Did you know that right now, while you're sitting still and listening, your heart is beating about once every second?
And it's been doing that since before you were born.
What?
Hello friends and welcome back to Sleep Tight Science a bedtime show that answers your questions about science.
You might be seeing hearts on cards and decorations everywhere right now.
Heart shapes on valentines, heart stickers, heart candies.
But the real heart inside your chest is doing something way more amazing than any drawing could show.
It's a pump that beats about 100000 times a day, pushing blood through thousands of miles of tubes in your body, delivering oxygen to every single cell that needs it.
And it does all of this without you ever having to think about it.
In this episode, we are going to try and answer the following questions.
How does your heart work?
And how does blood travel through your whole body and back again?
We'll start with what your heart is and how it pumps.
Four chambers, valves that open and close and the rhythm that never stops.
Then we'll follow the journey blood takes through your body one loop to your lungs to pick up oxygen, another loop out to your body to deliver it.
Finally, we'll explore why your heart speeds up and slows down and what you can notice about your own heartbeat.
You don't have to remember every word.
Try to remember this.
Your heart is a pump with four rooms, and your blood follows two loops.
One to your lungs to get oxygen, one through your body to deliver it.
Before we continue, here are some words to listen for.
Chambers, the four rooms inside your heart.
Two atria on top, two ventricles on bottom.
Valve, a one way door that keeps blood flowing in the right direction.
Artery, a tube that carries blood away from your heart.
Vein, a tube that carries blood back toward your heart.
Capillary, the tiniest blood vessels where oxygen moves from blood into your cells.
Pulse, the wave of pressure you can feel each time your heart beats.
A quiet thank you to Nancy May Nunes from Cheshire for introducing our show and to all our curious friends who send in questions.
You help us learn together.
Take a few deep belly breaths.
As you do, can you feel your heart beating?
Ready to explore the pump that's been working inside you your whole life?
Let's begin.
Your heart is a muscle about the size of your fist.
It sits in your chest, slightly left of the center, protected behind your ribs.
And it has one job.
Pump blood.
It beats continuously every second of every day for your entire life.
It never takes a break.
Not while you eat.
Not while you play. not even while you sleep.
But your heart isn't just one big room.
It's divided into four chambers, four separate spaces that work together in a carefully timed rhythm.
The two chambers on top are called atria.
Just one is an atrium.
There's a right atrium and a left atrium.
These are the receiving rooms.
Blood flows into the atria first.
They're smaller, with thinner walls, because they don't need to push very hard.
They just squeeze gently to move blood down to the next chambers.
The two chambers on the bottom are called ventricles.
There's a right ventricle and a left ventricle.
These are the pumping rooms and they have thick strong, muscular walls because their job is to push blood out of the heart and into your body.
The left ventricle is the strongest of all four chambers because it has to push blood all the way through your entire body, out to your toes, your fingertips, your brain.
So how does the pump actually work?
Blood flows into the atria.
The atria squeeze, pushing blood down through one-way doors called valves.
Those valves open to let blood into the ventricles below, then snap shut so blood can't flow backward.
Next, the ventricles squeeze hard, pushing blood out through more valves and into big tubes that carry it away.
Those exit valves close too, preventing blood from flowing back into the heart.
The sound of the valves closing.
Is what you hear as a heartbeat lub-dub.
Is the sound of the valves between the atria and ventricles closing?
The dub is the sound of the valves at the exits of the ventricles closing.
Lub dub, lub dub.
That rhythm happens about 60 to 100 times per minute when you're resting.
About 100,000 times a day.
Over 2.5 billion times in an average lifetime.
Your heart doesn't need you to tell it when to beat.
It has its own electrical system built right in special cells that act like a natural pacemaker, sending signals that keep the rhythm going automatically.
You don't have to think about it.
Your heart knows what to do.
Why does blood need to move at all?
Why a pump?
Because blood has jobs to do and sitting still, it couldn't do them.
Blood carries oxygen from your lungs to every cell in your body.
It carries nutrients from the food you eat.
It picks up waste like carbon dioxide and carries it away, but none of that works if your blood just sits in one place.
Your heart creates pressure, pushing blood through thousands of miles of tubes called blood vessels, so it can reach every part of you.
A baby's heart is about the size of a walnut.
A child's heart is about the size of their fist, and it grows as they grow.
An adult's heart is about the size of two fists side by side.
But no matter the size, the job stays the same.
Pump, pump, pump.
Steady and strong.
Take a slow breath and use your imagination for a moment.
A fist-sized pump working in the dark.
Four rooms, two on top, Two on bottom.
Doors opening, closing.
Opening, closing.
Blood flowing in, then out, then in again.
Lub dub, lub dub.
Quiet, constant, keeping everything moving.
Your heart doing its work.
In the next part we'll follow blood on its journey where it goes, when it leaves your heart, what it does along the way and how it finds its way back home.
Blood doesn't just slosh around randomly inside you.
It follows two specific loops, and your heart keeps both of them moving.
Loop one, to the lungs and back.
The right side of your heart handles this loop.
Blood that's traveled through your body arrives back at the right atrium.
It's carrying carbon dioxide, waste from your cells that needs to be removed.
The right atrium squeezes, pushing blood down through a valve into the right ventricle.
Then the right ventricle squeezes, pushing blood out through a big tube called the pulmonary artery and into your lungs.
In your lungs, blood travels through tiny capillaries wrapped around air sacs.
This is where the exchange happens.
Blood drops off carbon dioxide which you breathe out, and picks up fresh oxygen from the air you just breathed in.
Now the blood is oxygen-rich and ready to go back out into your body.
Oxygen-rich blood flows from your lungs back to your heart through tubes called pulmonary veins, arriving in the left atrium.
That's the end of Loop 1.
Loop two to your body and back.
The left side of your heart handles this loop, and it's a bigger job.
Oxygen-rich blood sits in the left atrium for just a moment, then the atrium squeezes, pushing blood down through a valve into the left ventricle.
The left ventricle is the strongest chamber and when it squeezes, It pushes blood out through the aorta, the biggest artery in your body, about as wide as a garden hose, or maybe about as wide as your thumb.
That's pretty big.
From the aorta blood flows through branching arteries that spread throughout your body like roads splitting into smaller and smaller streets.
Arteries carry blood away from your heart.
You can remember that because artery and away both start with the letter A.
Arteries have thick muscular walls because blood is under high pressure here, being pushed hard by your heart.
Eventually, arteries branch into the tiniest tubes, capillaries.
Capillaries are so small that blood cells travel through them single file.
This is where the delivery happens.
Oxygen and nutrients pass from the blood into your cells.
At the same time, carbon dioxide and waste pass from your cells into your blood.
Now the blood carrying waste starts its journey back.
Capillaries merge into small veins, and these small veins merge into bigger veins.
Veins carry blood back toward your heart.
They have thinner walls than arteries because the pressure is lower here.
Many veins have one-way valves inside them to keep blood from flowing backward, especially in your legs, where blood has to travel upward against gravity.
Eventually, all the veins in your body merge into two big veins called the vena cava and blood flows back into the right atrium.
The whole cycle starts again.
The entire journey out to your lungs, back to your heart, out through your body, back to your heart takes about 60 seconds.
Your heart pumps about 5 liters of blood per minute when you're resting.
That's your entire blood volume circulating once every minute.
So why two loops instead of one?
It keeps oxygen-rich blood and oxygen-poor blood separate.
Your lungs need gentler pressure.
So the right ventricle doesn't have to pump as hard.
But your body, fingers, toes, brain, muscles need stronger pressure to push blood all the way through.
So the left ventricle pumps with more force.
It's an efficient design.
Blood gets refreshed with oxygen before heading back out to do its job.
Close your eyes for just a moment and imagine one drop of blood.
Starts in the right atrium, flows to the right ventricle, then to the lungs, drops off carbon dioxide, picks up oxygen back to the left atrium, down to the left ventricle, then out through your body.
Deliver oxygen, pick up waste, And finally, back to the right atrium.
Around and around every minute of your life.
Tomorrow, you might notice just how much your heart does and how you can feel it working.
Let's talk about that next.
Here's what you can notice about your heart and circulation.
You can feel your pulse.
Your pulse is the wave of pressure your heart creates with each beat.
You can feel it at your wrist, on the thumb side, at your neck, even pressing gently on your chest.
Each pulse equals one heartbeat.
Notice how steady and rhythmic it is.
That's your heart's electrical system keeping time.
Beat after beat after beat.
Notice when your heart speeds up.
After running, climbing stairs, playing hard, your heart beats faster.
Why?
Your muscles need more oxygen when they're working.
Your heart pumps faster to deliver more blood. carrying more oxygen to meet the demand.
This is completely normal and healthy.
Your heart is responding to what your body needs.
You can notice when your heart slows down.
When you're resting, calm, lying down, your heart slows.
Slow, deep breathing can help your heart rate come down because your nervous system connects breath and heartbeat.
While you sleep tonight, your heart will beat more slowly because your body isn't working as hard.
When your hands are cold and you warm them up, notice how they turn pink or red.
That's blood flow increasing.
Capillaries opening wider to bring warm blood to your skin.
Blood carries heat, which is why you feel warmer when it flows near the surface.
Imagine how great this is.
Your heart has been beating since before you were born.
It started around three weeks after you began growing.
It will beat billions of times in your life.
You don't have to think about it, manage it, or remember to make it work.
It just does.
Tomorrow at breakfast or at dinner or any time you might talk about where you can find your pulse or when you noticed your heart beating faster today.
So back to our original question.
Your heart is a four chambered pump that beats in rhythm, pushing blood through two loops one to your lungs to pick up oxygen and one through your body to deliver it.
Valves keep blood flowing in the right direction and your heart adjusts its speed based on what your body needs.
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In this episode, we learned how your heart works.
We discovered it's a four chambered pump, two atria on top that receive blood and two ventricles on bottom that push it out.
We learned about the two loops blood follows one to your lungs to pick up oxygen and drop off carbon dioxide, and one through your entire body to deliver oxygen and pick up waste.
We found out how valves act like one-way doors, keeping blood flowing in the right direction, and how the lub-dub sound is valves closing.
And we explored how your heart adjusts, beating faster when you're active, slower when you rest, responding automatically to what your body needs.
Your heart has been working since before you were born and it will keep working every moment of your life.
Take a slow, deep breath in. and let it out gently.
Maybe tonight you'll dream of shrinking down and riding along, with a single drop of blood flowing through the four chambers, whooshing through valves as they open and snap shut like ancient doors.
You might travel through the lungs watching carbon dioxide drift away like smoke, while fresh oxygen rushes in like sparkling light.
Perhaps you'll journey through the branching highways of arteries getting smaller and smaller until you're squeezing single file through a tiny capillary delivering oxygen packages to waiting cells.
You could ride the slow current back through veins flowing upward against gravity, past one-way valves that click shut behind you.
Maybe you'll become a valve yourself, opening and closing in perfect rhythm, lub dub, lub dub, keeping the river flowing in just one direction.
Or you might watch the electrical signal spread across your heart like a gentle wave, telling each chamber exactly when to squeeze.
Your imagination can take you anywhere through the loops and chambers of your circulatory system.
Thank you for spending this time with us.
From Cheryl and Clark, good night, sleep tight.
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