The amazing human heart

Matters of the heart have baffled humans since the dawn of time, with sonnets and entire books devoted to the meaning of love. Now scientists are finding that the blood pump in your chest is just as complex. You can’t live or love without it.

The blood-filled muscle called the heart has become the universal symbol of love. The Greeks believed the heart was the seat of the spirit, the Chinese associated it with the center for happiness and the Egyptians thought the emotions and intellect arose from the heart.

Anatomy of the heart

About the size of our fist, the human heart is the most important muscle in the body. It can beat more than a hundred thousand times a day and pumping about two thousand gallons of blood through a sixty thousand mile network of vessels in the body.

In under a minute, your heart can pump blood to every cell in your body. And over the course of a day, about 100,000 heart beats shuttle 2,000 gallons of oxygen-rich blood many times through about 60,000 miles of branching blood vessels that link together the cells of our organs and body parts. That’s a hefty job for a fist-sized muscle.

The human heart is made up of four major chambers – right atrium, right ventricle, left atrium and left ventricle.  The right side of the heart receives blood that is low in oxygen from veins all over the body. It then pumps the blood through the pulmonary artery into the lungs where it will become reoxygenated.  The left side of the heart receives this oxygen rich blood from the lungs. Then it pumps the blood through the aorta back out to the rest of the body through a complex network of arteries, arterioles and capillaries.  While blood is circulating through the body, it delivers oxygen and nutrients to tissues through the capillaries and at the same time picks up carbon dioxide and other waste materials. The veins return the deoxygenated blood to the right atrium and the cycle begins again.

How do the heart valves work?

The heart has four valves. Each valve is like a one way door that keeps the blood in the heart flowing in the same direction. The valves are made up of two or three small but strong flaps of tissue called leaflets. Leaflets open to allow blood to flow through the valve and close to prevent blood from flawing backward. The opening and closing of the valves is controlled by blood pressure changes within each heart chamber. The tricuspid valve is positioned in the heart’s right side, between the right atrium and the right ventricle. The pulmonic valve separates the right ventricle from the pulmonary artery. The mitral valve is positioned in the heart’s left side, between the left atrium and the left ventricle, and the aortic valves separates the left ventricle from the aorta.

What is Coronary Heart Disease?

As blood is circulated through the heart, some of the blood circulates into a set of much smaller blood vessels that provide blood directly to the heart.   These arteries, called coronary arteries, surround or crown the heart. This separate circulatory system, called coronary circulation, keeps the heart nurtured and oxygenated. The two main branches of the aorta that nurtures the heart are the right and left main coronary arteries. Coronary artery disease which occurs when there is a buildup of cholesterol plaque that affects the arteries of this circulatory system and causes a decrease in the blood flow to the heart muscle – resulting in a possible damage to the heart or a heart attack.

What does the electrical system of your heart look like?

The beating of the heart, which is its rhythm, is regulated by electrical impulses generated by your heart muscle. These impulses begin in the sinoartrial node and cause your heart to contract. Sometimes the sinoartrial node is also referred to as your heart’s natural pacemaker since it keeps the heart rate constant and consistent. The impulses then travel to the atrioventricular node, where the signal is checked and has been sent to the ventricles which cause them to contract.

Your heart rate can change based on external conditions such as diet, exercise, stress or even hormonal factors (neural and hormonal effects).

What controls the beat of the heart?

There are two different factors involved in heart rate management: intrinsic and extrinsic controls. Intrinsic regulation of heart rate is the result of the unique nature of cardiac tissue – it is self-regulating and maintains its own rhythm without direction. Extrinsic controls are those that come from both hormonal responses as well as the commands from the nervous system: the central nervous system and the autonomic nervous system. Extrinsic regulation can cause the heart rate to change rapidly because of chemicals that circulate in the blood or by direct action of nerves that go to the heart.

A good example of this is to measure heart rate changes when certain words or emotions are said or felt without a muscle contracting. Say the words, “We are going to have a surprise test today” and watch heart rate extrinsically increase. Put on a heart rate monitor and sitting completely still watch a movie and watch heart rate jump during a car chase or action thriller. There is no cardiovascular or cardio respiratory change as a result of this change in heart rate; it’s simply the effect on the heart of chemicals and nerves responding to an external experience.

The cardiovascular control center for the body is located in the ventro-lateral medulla. Here heart rate slows if activated by the cardio inhibitory center in the medulla or speeds up if activated by the cardio accelerator.

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One Response to The amazing human heart

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