Heart structure and properties of heart muscle

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The heart is an organ which is composed mainly of one tissue called cardiac muscle, but also has an endothelium and connective tissue.  Because it is constantly beating i.e. the muscle is constantly contracting and relaxing (remember that muscle cannot "push") it requires a constant supply of energy.  Because the...

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The heart is an organ which is composed mainly of one tissue called cardiac muscle, but also has an endothelium and connective tissue.  Because it is constantly beating i.e. the muscle is constantly contracting and relaxing (remember that muscle cannot "push") it requires a constant supply of energy.  Because the heart wall is so thick, and the blood passing through it flows so quickly, heart mucles cannot get nutrients and oxygen from the blood passing through the heart.  Therefore the heart is supplied by a network of its own vessels.  When some of these coronary vessels are blocked, it can lead to death of parts of the heart wall and a subsequent myocardial infarction or MI.  This is often treated by "bypass" surgery where veins from the legs are used to replace the blocked coronary vessels.  Double and triple bypass, for example, mean that two or three veins have been used to replace the blocked vessels.  The veins are normally taken from the legs of the patient.  This does not cause problems as there is a network of veins in the legs and other veins open up more to compensate for those removed.

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