Original URL: http://www.theregister.co.uk/2006/12/23/the_odd_body_heart/

How does the heart differ from other mechanical pumps?

Biological efficiency

By Stephen Juan

Posted in Science, 23rd December 2006 11:02 GMT

Also in this week's column:

How does the heart differ from other mechanical pumps?

Asked by Andrew Lane of North York, Ontario, Canada

It is difficult to imagine a mechanical pump anywhere near as good in operating so well over so long as a human heart.

A heart is an organ that circulates blood around the body. Without the heart the body would not be able to receive the vital oxygen and nutrients that are carried by the blood. The blood also removes waste products. If the heart stops functioning, the body is starved of oxygen and will soon die if it is not restarted. Thus, it is one of the most important organs in the body.

This applies not only to humans, but to any other multi-celled animal. The adult human heart is about the size of a fist. It is made up mostly of tough muscular walls called the myocardium. This is lined on the outside by a thin layer of tissue called the pericardium and on the inside by another thin layer called the endocardium.

Human hearts have four chambers and are divided into left and right. The upper chamber on each side is called an atrium (or auricle) while the lower chamber is called a ventricle. The atria receive blood entering the heart and the ventricles pump it out.

Valves in the heart make sure that the blood only flows in one direction. The muscle cells of the heart are long and tough. They contract and relax in time with each other. When the heart relaxes, blood flows into the atria from the body through the arteries. This is known as the diastole.

The healthy heart has a natural pacemaker called the atrioventricular or AV node. This is an area of tissue between the atria and the ventricles that conducts electrical impulses from the atria to the ventricles. These impulses first make the atria squeeze blood into the ventricles. The ventricles then contract pushing blood into the arteries. This is known as the systole. The process repeats itself over and over again throughout our lifetimes.

The heart keeps up a steady rhythm averaging 60 to 80 beats a minute in an average adult at rest. It can go slower when we sleep or faster when we are active.

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