Phlebotomy: The Heart Structure

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Posted on 25th October 2010 by admin in Uncategorized

The heart is the most important part of the circulatory system.  It is responsible for pumping blood throughout the body and is located in the thoracic cavity, between the lungs.  The apex or tip of the heart points down and to the left of the body.

Slightly larger than a man’s closed fist, the heart is a four chambered muscular organ.  It is slightly hollow and is surrounded by a fluid sack called the pericardium.  The pericardium wall has three distinct layer- the epicardium, myocardium and endocardium.  The epicardium is the thin outer most layer.  It is often filled with fat, especially in older people.  The middle layer, the myocardium is composed mostly of muscle.  It forms the bulk of the heart and is the layer that contracts.  The endocardium is the thin inner layer of the heart that lines the heart chambers and covers the fibrous skeleton of the valves.

The heart is composed of four chambers.  The upper chambers of the heart are the called atria.  The lower chambers of the heart are called ventricles.  Functionally, the atria are receiving chambers for blood returning to the heart from the circulation.  These small, thin-walled chambers only need to contract minimally in order to push blood into the lower ventricles.  The ventricles make up most of the volume of the heart.  They are the discharging chambers of the heart and are considered the actual pumps of the heart.  The right ventricle pumps blood into the pulmonary trunk.  The left ventricle ejects blood into the aorta.

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