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.
- The heart was once believed to be the seat of human emotions. Our language contains many references indicating this: "Heart break", "heart warming", "cold hearted", "bleeding heart", "heart felt", and so on. This association between the heart and emotions probably comes from the fact that when we are emotionally overcome, we feel it in the chest, rather than in, say, the feet.
- The ancient Egyptians rightly understood that the heart pumped blood, but believed that it did this to give orders to the body. In a sense, they were right.
- The ancient Egyptians believed that the heart was where a person's soul resided. In the afterlife, a person presented their heart to the god Anubis. This is the Greek name for the Egyptian god with the body of a man and the head of a jackal. Anubis weighed the heart. If the heart was light, the person was deemed good and was entitled to go further into the underworld. But if the heart was heavy, the heart and its owner were fed to the goddess Ammit. This is the Greek name for the Egyptian goddess with the body of a lioness and the head of a crocodile (Amheh in Egyptian).
- A newborn baby's heart beats at about 130 beats per minute.
- Science has discredited the view that one can predict the sex of the baby by its heart rate in utero. Still, many believe it is true. They say, a little faster, a girl, a little slower, a boy.
- Dr Sally Edwards, CEO of Heart Zones has proposed a set of gender specific formula for predicting Maximum Heart Rate. For males: 210 minus one half your age minus 1 per cent of total body weight plus 4. For females: 210 minus one half your age minus 1 per cent of total body weight plus 0.
- The heart pumps about five to six litres (10.5-12.6 US pints or 8.8-10.5 BR pints) of blood around the body every minute while you are at rest.
- Elephants have a heartbeat of 25 beats per minute.
- Hummingbirds have a heartbeat of about 1,000 beats per minute.
- The two thumping sounds of the heart are caused by the shutting of values. They are known as "lub" and "dup".
Stephen Juan, Ph.D. is an anthropologist at the University of Sydney. Email your Odd Body questions to [email protected]