Andrew Curran - Get off the Sofa: A prescription for a healthier life by Dr Andrew Curran the wellness doctor

In each chapter I am going to tell you about a system in your body. First Im going to tell you how it works. Then Im going to tell you how to look after it. Then Im going to tell you how to wreck it. Simples.

The heart is a pump. Nothing more and nothing less. Just a pump.

It is not where love resides nor is it the repository of your emotions. That is just so much Walt Disney. Blood flows into the heart from a great big vein called the vena cava (coming from the body) on the right and another huge vein called the pulmonary vein (coming from the lungs) on the left. It keeps flowing until the big pumping chambers, the ventricles , are nearly full. Then the two atria contract and force the last little bit of blood into the ventricles through the mitral valve on the left and the tricuspid valve on the right. This fills the ventricles right to the top. Once they are full, the ventricles contract. The ventricles (unlike the atria) have really thick, strong walls.

Their contraction slams the mitral and tricuspid valves shut and forces the blood out through the pulmonary valve into the lungs on the right and through the aortic valve into the body on the left.

When you are resting this happens 6080 times a minute. When you are taking what your body finds to be heavy exercise this can happen as often as 200 times a minute.

So there you have it. A simple four chamber, parallel flow pump.

So what happens to all that blood? Blood from the right ventricle is pumped out into the lungs, or rather into the blood vessels that direct blood to the correct places in the lungs. Those correct places are called the alveoli. They are the air spaces in your lungs where you get rid of a gas called carbon dioxide (which is a poison if you have too much of it in your blood) and take in oxygen (which you need to stay alive) you probably knew that! The blood flows on through the lungs (now full of oxygen and having got rid of its carbon dioxide) and back to the left side of your heart. From there it is pumped out into your body. This is a pretty impressive bit of pumping. You have miles and miles of blood vessels in your body estimated at between 50,000 and 100,000 miles. The left side of your heart not only gets enough pressure going to force your blood out through all those miles of blood vessels, but it keeps enough of a pressure head up to get it all the way back to the right side of your heart. Once it reaches there, off it goes again into the lungs to start the whole process all over.

Out there in your body the blood gives up its precious cargo of oxygen to your cells so they can do all the work they have to do. It also picks up all that poisonous carbon dioxide to carry it back to your lungs to get rid of it.

But blood doesnt just do that.

It is after all the most precious fluid in your body. As an adult you have about 5 litres of the stuff. Actually its mostly water with bits and pieces floating in it. Dissolved in the water are all the salts (like sodium and potassium) and a whole pile of what are called trace elements like selenium and zinc which are essential to maintain the health of your cells. Floating in the water (as opposed to being dissolved in it) are lots of other things. Proteins hang out there. These range from simple proteins like antibodies (which are the guided missiles of your immune system) to complex beautifully structured protein moieties like the complement system, a collection of proteins that are crucial to getting your blood to clot. But even bigger things float around in your blood. Red blood cells are bi-concave discs that are responsible for carrying oxygen around the body. They contain haemoglobin, an ber-specialist protein that actually carries an iron molecule wrapped in its coils. There are the white blood cells, mindless aggressors that target and destroy any foreign proteins they find, like bacteria and viruses. And finally there are all the rich variety of cell foods and building blocks like dextrose and amino acids and fatty acids. Its a real wonderland your blood.