l8o ANATOMY AND PHYSIOLOGY 



The semilunar valves allow the blood to flow in one direction 

 only that is, away from the heart. 



FUNCTIONS OP THE CHAMBERS OF THE HEART 



The auricles, having received blood from the veins opening into 

 them (the right blood from entire body; left from lungs alone) 

 gently contract together to send it down into the ventricles; 

 quickly the ventricles contract, forcibly and together, expelling 

 blood into the two large arteries the pulmonary carrying it to the 

 lungs, the aorta to all parts of the body. This process is the systole 

 of the heart; it occupies about eight-tenths of a second, perhaps a 



FIG. 122. (DIAGRAM.) 



The right auricle receiving blood and passing it through tricuspid valve into right 

 ventricle, which is dilated (semilunar valves closed), (Dalton in Brubaker.) 



trifle more. Then comes the resting-time when the heart is dilat- 

 ing and filling again, called the diastole of the heart. 



One systole and one diastole together constitute a cycle of 

 the heart. 



During the systole of the auricles, the tricuspid and mitral 

 valves are open and the semilunar valves are closed. During 

 systole of the ventricles the tricuspid and mitral valves close, and 

 the semilunar valves are open (Figs. 122,123). See Heart Sounds 

 (closure of valves) . 



The thickness of the ventricle wall is explained by the need for 



