How Your Heart Works?
The heart is just a pump. All it does it pump blood around the body. The two chambers of the left side of the heart pump blood rich in oxygen from the lungs to the rest of the body. The two corresponding chambers of the right side of the heart take the oxygen-spent, carbon dioxide-rich blood from the body back to the lungs. In the lungs the blood gives up the carbon dioxide - the waste material from the body's energy-burning processes - to the air, and takes in more oxygen.
These are the bald facts. But there is no human-designed pump that could do the heart's job. No engineer has yet made a pump that acts around 70 times a minute, for upwards of 70 years, all the time maintaining and repairing itself and supplying its own energy and fuel. And not once, in all that time, stopping for a rest.
The secret lies in the special properties of the heart muscle. Try to do with your leg muscles what you take for granted that your heart does. Run on the spot so that each foot touches the ground just a little faster than once a second. Step high as you do it, so that your thighs come up to the horizontal with each step. See how long you can carry on before your legs get tired, and have to rest.
If you are relatively unfit, you may last as long as five minutes. Athletes, of course, can go on for an hour or more. But do it day and night, without stopping to sleep and rest? For years? Impossible for even the greatest marathon runner.
Yet that is what the heart does, day in, day out, all our lives. Most of the time we do not give it a second thought. Of course, that is a good thing: people who are constantly aware of their heartbeat can become neurotic and obsessional about it, and their lives can be ruined. In the early days of heart valve surgery, some valve models gave out a 'ping' with each beat. Their owners could hear it plainly, especially at night, and were often, understandably, upset about it.
Yet we need a happy medium in our relationship with our hearts. The more we understand about how the heart works, the better care we should be able to take of it, and the less frightened we should be when it shows signs of going wrong.
First of all, the heart is all muscle, the myocardium (muscle = myo, heart = cardium). It differs from all other muscles in the body by having an astonishing capacity for rapid recovery after it has been 'fired' by nerve impulses to contract, or 'beat'. Given the signal to contract by a special network of electrical fibres exclusive to it alone, it completes its cycle of shortening and lengthening within a fifth of a second, then has three-fifths or four-fifths of a second to recover before it is asked to beat again.
During that vital resting period, the muscle reorganizes itself so that it can contract again without tiring. In the process of contraction it takes oxygen from the blood. Oxygen is the fuel that converts the heart muscle's store of glucose into the energy needed so that it can beat. In the resting period between beats, each muscle fibre has to take up more oxygen and glucose to repeat the cycle. Without the constant flow of oxygen and glucose from the bloodstream, the heart muscle cannot work. It will first complain, and then die. Give it enough nutrients and oxygen and it will keep going for a lifetime.
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