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HUMAN PHYSIOLOGY 



6. Action of the Valves of the Heart. 



A. Auriculo-ventricular (Fig. 115). These valves have 

 already been described as funnel-like prolongations of the 

 auricles into the ventricles. They are firmly held down in 

 the ventricular cavity by the chordae tendineae. When the 

 ventricle contracts the papillary muscles pull the cusps of the 

 valves together and thus occlude the opening between auricles 

 and ventricles. The cusps are further pressed face to face by 

 the increasing pressure in the ventricles, and they may become 

 convex towards the auricles. They thus form a central core 

 around and upon which the ventricles contract. 



On the -left side of the heart the strong anterior cusp of 

 the mitral valve does not materially shift its position. It 



FlG. 115. State of the various parts of the Heart throughout the Cardiac Cycle. 

 1, Auricular Systole ; 2, Beginning of Ventricular Systole (latent period) ; 

 3, Period of Outflow from the Ventricle ; 4, Period of Residual Contraction ; 

 5, Beginning of Ventricular Diastole. 



may be somewhat pulled backwards and to the left. The 

 posterior cusp is pulled forwards against the anterior. 



On the right side the infundibular cusp of the tricuspid 

 valve is stretched between the superior and inferior papillary 

 muscles, and is thus pulled towards the bulging septum, 

 against which it is pressed by the increasing pressure inside 

 the ventricles. The posterior cusp has its anterior margin 

 pulled forward and its posterior margin backwards, and is 

 thus also pulled toward the septum. The septal cusp 

 remains against the septum. The greater the pressure in 

 the ventricle the more firmly are these cusps pressed against 

 one another or against the septum, and the more completely 

 is the orifice between the auricle and the ventricle closed. 

 On the right side of the heart other factors play an impor- 

 tant part in occluding the orifice ; the muscular fibres which 



