Matters of the heart

Matters of the heart

What do you really know about your heart?

In your lifetime your heart will beat around three billion times and pump enough blood to fill 5,500 large swimming pools!  Pretty good going, and luckily, unlike most of your muscles, your heart never gets tired.  It works day and night to pump blood around your body.  Even when you're resting, your heart works twice as hard as your leg muscles would if you started sprinting!

heart_chest

Clench your fist, that's about the size of your heart. This is quite small for one of the most powerful muscles in your body.  It is so powerful that it can squirt blood at a distance of 10 metres!

Most people think their heart is on their left side of the body because it tips slightly to this side. In fact, it sits in the middle of the chest, just in between your lungs.  Your left lung is actually a bit smaller to make room for your heart.

Your heart has to work hard because it carries oxygen in the red blood cells all over your body.  Its design is very clear. Blood needs to be pumped to the lungs before it can make its way around the body, but by the time the blood has gone through the lungs it has lost a lot of pressure.  So the heart is made of two pumps.  The right side pumps the blood to the lungs to get oxygen.  Then the left side gets the oxygenated blood and pumps it all round the body.

Both sides of the heart have an atrium and a ventricle.  When the blood arrives at the heart it goes into atrium.  It the gets pushed through a valve into the ventricle.  Then the stronger muscles around the ventricles push the blood back out of the heart.  It is these two pushes which make the distinctive da-dum of your heart beat.  The second push is more powerful and this is why it gets louder.  The wall of the left ventricle is much thicker, because the muscle has to push the blood a lot further.

circulatory_system

The veins and arteries which connect to the heart are also different.  The aorta is the artery which takes the blood away from the heart to the rest of the body.  It is the biggest artery in the body, and its diameter is about the same size of a garden hosepipe!

Our hearts normally beat 72 times a minute - that's quite a lot when you think about it.  Compared to this a blue whale's heart only beats 6 times a minute, and a Hummingbird's heart can beat around 1000 times a minute. But a Hummingbird's heart is only the size of a grain of rice; the heart of the Blue Whale is the same size as a car!

And if you ever thought your dog loves you more than anyone else maybe it's because they have the largest heart to size ratio.  This means they have the biggest heart of any animal relative to its size.

Doctor Who is an alien who has more than one heart, that's just sci-fi isn't it?  Well there are actually some creatures a little closer to home that also have more than one heart.  Octopuses and squid have three hearts!  They have two hearts which pump blood to the gills.  The third heart pumps blood to the rest of the body.

octopus.jpg

There are actually some humans who have more than one heart.  But they weren't born with them.  It is called a piggyback heart and it is a type of heart transplant.  It is used for patients with cardiomyopathy, which can make the heart grow to twice the size it should be; the heart could then stop working.  But instead of replacing the heart with a donor heart, they just disconnect some of it and hook up the new heart right next to it.  So the new heart takes over most of the pumping and the old heart carries on working but with reduced pressure.

In 2005 there was a major breakthrough in the field when Hannah Clark had the operation reversed!  She was given the second heart as a baby but 10 years later her body rejected it.  Because her old heart had been resting all this time it was able to function properly again so doctors hooked up her old heart and it began beating all by itself again.  Follow the link to find out more about Hannah and her amazing story:

http://news.bbc.co.uk/1/hi/health/4904914.stm

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