Saturday, December 20, 2008

The Heart: Powerhouse of the Body

The heart truly is an amazing organ. It alone is responsible for circulating blood to every organ and cell of the body, and from the moment it starts beating, it does not cease until death. It is regulated to increase its beats per minute during exercise, and to slow down after exercise ceases. It responds to the body’s need for nutrients and oxygen by increasing circulation of the blood. Here are a few facts about this life sustaining organ that most people don’t know.

1) Even at rest, the muscles of the heart are contracting harder than the leg muscles in a person sprinting.
2) There are roughly 5.6 liters of blood in the human body; the heart is able to circulate this volume of blood 3 times around the human body in a minute.
3) The average heart beats about 100,000 times a day, equal to 35 million times a year and 2.5 billion times in an average lifetime (70 years).
4) The system of blood vessels in the human body (including arteries veins and capillaries) is over 60,000 miles long, and the human heart is able to supply blood to every inch of it.
5) The heart pumps enough blood during its lifetime to fill 3 super tankers.
6) The heart is able to accomplish all these amazing tasks, and only weights between 8 and 10 ounces in a grown adult.

The primary responsibilities of the heart are to transport oxygen and nutrients to organs and cells throughout the body, and pick up and rid the body of carbon dioxide and wastes from these cells. The nutrients are transported in the blood’s medium, plasma, while the oxygen is bound to the incredibly important protein hemoglobin, found in red blood cells. Each of these hemoglobin molecules can bind 4 oxygen molecules, and there are over 270 million molecules of hemoglobin in each red blood cell. Therefore red blood cells are able to transport very large amount of oxygen. These red blood cells give the blood its characteristic red color, and are pumped throughout the body at an astonishing rate by the heart.

With each beat the heart pumps two to three ounces of blood into circulation. For the heart to work efficiently the blood passes through a series of chambers in the heart, the blood first enters either the right or left atrium, then is pumped into the right or left ventricles to be pumped to the lungs or throughout the body. There are several valves in the heart to prevent backflow of blood that would otherwise occur due to the high pressure that the blood is subjected to in order to speedily and effectively travel throughout the body.

The contractions of the heart are actually controlled by an electrical signal that travels along the heart. The first signal originates at the SA node which causes both atria to contract and force blood into the ventricles, this signal travels down the heart to the AV node located on the other side, where there is a pause while the ventricles fill with blood, then the AV node signals both the ventricles to contract. This electrical system accounts for the rhythmic beating which allows blood to be pumped most effectively. The resting phase of this system is called diastole, while the contracting phase is called systole. The flow of blood through the heart causes the valves talked about earlier to open and close, giving rise to the lub-dup sound of the heart beating.

The pulse is usually an accurate reading of the heart rate of a human adult, it is a result of arterial expansion due to the increase in pressure of the blood during systole. This wave of arterial expansion begins as blood leaves the heart and travels the lengths of the arteries in the body, gradually weakening in strength as it goes. As you place your fingers on your artery you can feel the expanding and shrinking of the artery as the blood passes through it. A chart of average pulse rates is given below:

Blood pressure is a measure of the systolic and diastolic pressures of the blood traveling through the human body. Blood pressure is measured in millimeters of mercury, a common unit for pressure, and is measured by wrapping a cuff around a person’s upper arm and inflating the cuff to a high pressure and gradually releasing the pressure in the cuff. When blood is first able to pass through the artery collapsed by the inflated cuff this is the systolic pressure, because it is at a higher pressure. When blood is no longer able to be heard passing through the artery using a stethoscope this is the diastolic pressure. As we mentioned before systole is when the heart is contracting, and diastole is the phase when the heart is resting. A chart of blood pressures ranging from optimal blood pressure to stage 3 hypertension (high blood pressure) is given below:

Many factors can affect both blood pressure and pulse, exercise being the first that comes to mind when most people are asked. Exercise increases the number as well as the strength of heart contractions because the body has a higher need for oxygen and nutrients in its muscles. This therefore increases both pulse and blood pressure. Obesity affects both of these as well because, in people who don’t exercise, the heart is out of shape and does not pump as effectively, and therefore must beat more times than the average person to reach all areas of the body. Blood pressure is increased by obesity as well.

The heart truly is a miracle of the human body. It pumps an astonishing amount of blood throughout the body every day and never takes a moment of rest from the time it starts beating until death. Without this amazing organ life would not be possible.


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