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heart
(hahrt)
a hollow muscular organ to the left of the midline of the chest that serves as a pump controlling blood flow in the pulmonary and systemic circulation. The septum, a thick muscular wall, divides the heart into right and left halves, each with an upper chamber called the atrium and a lower chamber called the ventricle. The right atrium receives deoxygenated blood from the superior and inferior venae cavae and sends it through the right ventricle into the pulmonary circulation. The left atrium receives oxygenated blood from the pulmonary vein and sends it through the left ventricle into the aorta and the systemic circulation. Cardiac valves connect the chambers of the heart with each other and with the circulatory system; they can open and shut in such a way as
to keep the blood flowing in one direction through the heart and out through its appropriate arteries. The heart wall is composed
of three layers of tissues. the interior, membranous endocardium, the muscular myocardium, and the exterior, thin but sturdy pericardium. The heart is made up of special muscle tissue capable of continuous rhythmic contraction without tiring. The impulse that
starts the contraction of the heart originates in the sinoatrial node, which is special tissue that acts as the normal pacemaker for the heart.
Structures of the heart.
Copyright 2007. An Elsevier publication. All rights reserved.
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