The left atrium and its auricle appendage receive oxygenated blood from the lungs through four pulmo

The left atrium and its auricle appendage receive oxygenated blood from the lungs through four pulmo

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The left atrium and its auricle appendage receive oxygenated blood from the lungs through  four pulmonary veins (two from each lung). The left atrium, like the right atrium, is a holding  chamber for blood in readiness for its flow into the left ventricle. When the ventricles relax,  blood leaves the left atrium and passes through the left AV valve into the left ventricle. The left  AV valve is also called the mitral or bicuspid valve, the only heart valve with two cusps. The left ventricle is the pumping chamber for the systemic circulation. Because a greater  blood pressure is required to pump blood through the much more extensive systemic  circulation than through the pulmonary circulation, the left ventricle is larger and its walls are  thicker than those of the right ventricle. When the left ventricle contracts, it pumps oxygenated 
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Unformatted text preview: blood through the aortic semilunar valve, into a large artery, the aorta, and throughout the body. The following events occur in the left ventricle, simultaneously and analogously with those of the right ventricle: 1. When the left ventricle contracts, the left AV valve closes and prevents blood from moving back into the right atrium. As in the right AV valve, the chordae tendineae prevent overextension of the left AV valve. 2. When the left ventricle relaxes, this results in less pressure in the left ventricle and higher pressure in the aorta. This high pressure causes the aortic semilunar valve to close, thus preventing the return of blood to the left ventricle....
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