Sep
3
2011

STRENGTH, RHYTHM AND SPEED OF THE HEART

The strength, rhythm and speed of our heart’s pumping action to a large extent determine our health.  Our heart, is a muscular structure about the size of our fist, and a 60,000-mile network of blood vessels make up our cardiovascular system.  The muscle responsible for pumping the blood to all tissues of our body is called the myocardium (myo means “muscle”, cardia means “heart”).

Our heart is located slightly to the left of the center of our chest.  It is protected by our breastbone (sternum) in front, our spinal column in back, and our lungs.

The right side of our heart projects toward the front of our chest; the left side is toward our back.  In the adult, the heart weights about 3/4 pound.

Our heart has four chambers.  Two atria on top are receiving chambers for blood returning from veins.  Two ventricles underneath pump blood into our arteries.

The two sides of our heart are functionally linked in a figure-8 loop connected by arteries and veins of our lungs and the rest of our body.

Our heart is shaped like a cone, with the point (apex) at the bottom and the broader part at the top.  The apex of our heart is the tip of the ventricles.  It points down to the left side of our chest.  The wider upper part of our heart includes the right and the left atria and the origins of the major blood vessels.

Our heart has three layers of tissues: the myocardium, the epicardium, and the endocardium.  The myocardium is the thick main layer of heart muscle, made up predominantly of cells called myocytes.  Its outside surface is covered by a thin, glossy membrane called the epicardium.  Another smooth, glossy membrane, the endocardium, covers the inside surfaces of our heart’s four chambers, the valves , and the muscles that attach to those valves.

How our heart pumps

Our heart functions by squeezing blood out of its chambers (contraction) and then expanding to allow blood in (relaxation).  The action is like squeezing water out of a soft plastic bottle while holding it under water, and then releasing your grasp so that water is sucked back into the bottle.

This cycle of contraction and relaxation causes blood flow to be “pulsatile.”  We can often feel our heart beat by touching our chest.  The pulse of blood flow is also transmitted to our blood vessels, so we can feel our pulse at places where large arteries close to our body, such as our wrist, neck and groin.

The Cardiac Cycle

The period from the beginning of one heartbeat to the beginning of the next is called the cardiac cycle.  The cardiac cycle consists of a period of contraction (systole) followed by a period of relaxation (diastole)

Blood is pumped out of our heart during systole.  During diastole, our heart relaxes and refills.  During systole our heart pumps (squeezes).  During diastole it relaxes (dilates).

Our heart must be fully relax before it can pump again.  This allows it to refill with blood.  At 70 beats a minute, the cardiac cycle lasts about 8/10 second.

If you are healthy, resting adult, your heart will beat about 60 times every minute, more than 86,000 times each day, and over 2 billion times in an average lifetime.  Our heart will pump 3 ounces of blood with each beat.  That amounts to 5.5 quarts every minute and over 2,000 gallons daily. During strenuous exercise, Our heart may have to pump four to seven times the amount of blood it pumps at rest.

No matter how forceful the contraction, our heart does not pump all the blood out of both ventricles with each beat.  Doctors call the portion of blood that is pumped out of a filled ventricle the “ejection fraction.”

A normal ejection fraction is 50 percent or more. So at least half the blood in the ventricle is pumped out on each beat.  The ejection fraction is a good indicator of the overall function of our heart.  In a healthy person, the ejection fraction of the heart might increase by about 5 percent with exercise.  It can diminish to 20 to 30 percent or lower if the ventricles are not functioning normally.

Nicetas

About the Author: Nicetas Juanillo

Writing makes me happy away from home. My website is where you can find my tips about lifestyle, health and other issues. I also have books on my site that you can read to know more

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