A) pushing open of the venous valves
B) suction pull
C) stimulation of the sino auricular node
D) pressure difference between the caval and atrium
Correct Answer: D
Solution :
The action of heart includes contractions and relaxations of the atria and ventricles. Contraction of the heart is called systole and relaxation is called diastole. The dynamics of blood flow in blood vessels is no exception and blood flows through the blood vessels along a pressure gradient, always moving from higher to lower pressure areas. Fundamentaly, the pumping action of heart generates blood flow. The 'contraction of atria is initiated and activated by sinoatrial node (SA node?Pacemaker), which spreads waves of contraction across the wall of atria via muscle fibres at regular intervals.
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