Custom Search
|
|
 
|
||
|
Heart Functions The heart acts as four interrelated pumps. The right atrium receives deoxygenated blood from the body via the superior and inferior vena cava. It pumps the deoxygenated blood through the tricuspid valve to the right ventricle. The right ventricle pumps the blood past the pulmonary valve through the pulmonary artery to the lungs, where it is oxygenated. The left atrium receives the oxygenated blood from the lungs through four pulmonary veins and pumps it to the left ventricle past the mitral valve. The left ventricle pumps the blood to all areas of the body via the aortic valve and the aorta. The heart's constant contracting and relaxing forces blood into the arteries. Each contraction is followed by limited relaxation or dilation. Cardiac muscle never completely relaxes: It always maintains a degree of tone. Contraction of the heart is called systole or "the period of work." Relaxation of the heart is called diastole or "the period of rest." A complete cardiac cycle is the time from onset of one contraction, or heart beat, to the onset of the next.
Figure 1-33.-Frontal view of the heart-arrows indicate blood flow. |
 
|
|
|
||
