Take care of your heart – the engine of life

(Part 3 of a series on Valentine)

"In love, your heart skips a beat."

The heart is a favorite subject of singers, writers and poets. Sadly their words are not really accurate. Love, courage and kindness come from the brain, not the heart. Yet even the clever brain relies on the heart to survive.

Pear shaped heart

The heart is not really ‘heart’-shaped, as in cartoons about love. It is more like a squashed pear or pointy-ended potato lying on its side.

It is like a hollow bag, about the size of its owner’s clenched fist. In an average adult male, the heart weighs about 300 grams, nearly the same as a medium grapefruit. In a typical woman, the heart weighs about 250 grams. The lowermost pointed tip of the heart is about level with our sixth rib.

The heart, blood and all the blood vessels make up about 1/10th of the weight of the whole body. If all the blood vessels in the body could be joined end to end, they would go around the world more than twice. If the body was as big as a large city like London or New York, its main blood vessels would be like motorways 150 meters across and its tiniest vessels would be about the width of a pencil.

Meantime, blood makes up about 1/12th of the weight of the body. In an average woman, the volume of blood is 4 to 5 liters, while 5 to 6 liters in a typical man. At any one moment only 1/20th of the body’s blood is in the capillaries. Around three quarters is in the veins.

Two in one

The heart has muscular walls with four hollow chambers inside. The two lower chambers, ventricles, are much bigger with thick muscle walls. Each atrium connects to the ventricle below it through a flap-like valve. After the atria fill, they contract and the valves open to allow blood through to the ventricles. The valves shut when the ventricles contract to stop blood flowing back. The valves open as the ventricles contract and blood rushes out into the arteries.

The heart is not a single pump, rather, it is two pumps side by side. So the body really has two circulations. The short one to the lungs and back to the pulmonary circulation, the long one all around the body is the systemic circulation, which means the blood goes to the central main artery, the aorta, then to the head, arms, abdomen, legs and the rest of the body.

Mechanical pumps last 10 or even 20 years. The human heart continues for 70, 80 or even 100 years. It is one of the most efficient pumps ever evolved, beating approximately 2.5 billion times in a lifetime of 70 years.

The heart beat

The sounds of the valves opening and closing make the sound of each heartbeat, ‘lub-dup’. The heart beats almost every second, without you even noticing it. The average heart rates at rest become slower with age, from 130 per minute in a new baby, to 100 for a one year old, 80 in an 8-year old child, while 60-80 in an adult. When the body is relaxed, each heartbeat in an adult pushes 75 ml of blood out into the blood vessels. So, a heart would fill a bathtub in 35 minutes.

When relaxed, a heartbeat is slow and steady, but when the body is active, the heartbeat gets faster and harder, and you feel it pounding inside your chest. The heartbeat is caused by tiny electrical signals passing through its muscle. The signals can be detected by sensors on the chest, and shown as spiky lines on the ECG (electrocardiograph).

The heart cannot relax and must keep working at all costs

The heart is one bag-shaped muscle of our body, which cannot relax and must keep working at all costs. This muscle-powered pump for the circulatory system beats every second to force blood through the network of blood vessels.

Our blood goes around and around or circulates through the body. It delivers oxygen to all body parts, organs and tissues. Blood also carries hundreds of other substances. These include energy-packed sugars, nutrients for growth, vitamins and minerals to keep the body working well, disease-fighting microscopic white cells, and the ‘messenger’ substances known as hormones, which control many bodily processes.

The body’s circulatory system works like a giant production line. There are branches into every area. Vehicles come and go as they drop off fresh supplies and gather up wastes.

The blood not only delivers – it collects, too

Blood not only delivers – it collects, too. It gathers up wastes for removal by other body parts. These are the two lungs, which get rid of the waste carbon dioxide, and the two kidneys, which filter unwanted substances from the blood to form the liquid urine. Blood also helps to keep our bodies at a regular temperature. It spreads heat from hard-working parts, like the heart and muscles, to cooler areas. If the body goes too hot, more blood flows through the skin and loses the extra warmth to the atmosphere.

Any kind of movement means muscles work harder and need extra supplies of oxygen, as well as energy. So the heart pumps harder and faster to increase blood flow through the muscles.

Wave of pressure

Blood does not slosh around the body like water in a barrel. It flows through a network of tubes called blood vessels. There are three main kinds of vessels – each different in size and structure.

Blood vessels leading from the heart are known as arteries. The largest are about the width of a thumb. Arteries have thick walls, which are very tough and stretchy. Blood comes out of the heart in a surge of pressure and this makes the artery walls bulge. As this high pressure surge travels out into the artery network, all of the arteries around the body bulge with it.

As arteries divide they become narrower and their walls get thinner. They lead to all body parts, including the heart itself. Finally, they divide into the smallest kinds of vessels, capillaries. The walls of a capillary are so thin that oxygen and other substances can seep through them from the blood inside, to the cells and tissues around. Waste substances move the other way, into the blood.

Blood fighting disease

Germs are everywhere – in air, water and soil and on almost every object. But, the body fights a silent, never-ending war against them, and lucky for us, usually wins. The invisible armies, which defend us against germs and disease make up the immune system.

Some of the best ‘soldiers’ in the immune system are white cells, with thousands in every drop of blood. There are different kinds. Some attack germs directly, ‘eating’ them whole. Others make natural body substances called antibodies which stick onto germs so that they die.

Around the world billions of people are protected from infections by immunizations. The immune defense system learns to recognize and fight them. Later, if the real germs invade, the defenses kill them before they can multiply. This process is called immunization.

Health watch!

Like any other pump, the heart if it becomes clogged, becomes less efficient – or even stops working altogether, threatening life itself.

Plaques of fatty substance called cholesterols are deposited on the walls of blood vessels from early adulthood onwards. Eventually, this deposit may block the coronary arteries that supply blood to the heart muscle itself and cause heart disease.

Partial blockage may result in Angina. When blood clots in a blood vessel, heart chamber of other site within the body, this is called thrombosis. More seriously, if a blood clot lodges suddenly in a coronary artery and blocks it completely, part of the heart is starved of oxygen, causing a heart attack or even stopping the beating altogether.

What we eat, drink and do every day all have huge effects on our heart and blood vessels. In some of the world’s wealthiest countries, heart and circulation problems are among the leading causes of illnesses. Medical surveys show that habits to keep the heart healthy begin when young. They include avoiding eating too many fatty foods, especially animal fats, also avoiding too much salt, taking regular exercise and not smoking. It is never too early to begin living healthy!

Both hearts and lungs make up the whole heart story of life

Astronauts, American firefighters in smoke-filled buildings and deep-sea divers have one vital feature in common – their own air supply. The human body cannot last for a few minutes without taking in the substance oxygen, found in the air around us. But, breathing fresh air into the lungs is only half the story. Once the oxygen is inside, it must then spread all around the body, to every tiny nook and cranny. This is the job of the heart and blood.

When we are active, our bodies have to work harder. They take in more oxygen as we breathe faster, and our heart pumps blood round our bodies more quickly.

(Reference: Body Atlas – Lungs, Heart and Blood by Steve Parker)

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