Final answer:
The two main phases of heart action are diastole and systole. During diastole, the heart is relaxed and blood flows into the heart. During systole, blood is pumped out of the heart. The path of blood flow starts with blood flowing into the relaxed atria and ends with blood being pumped into the arteries.
Step-by-step explanation:
The two main phases of action that occur as the heart relaxes and then contracts are diastole and systole. During diastole, the heart is relaxed, and blood flows into the heart. The atria contract and pump blood into the ventricles, while the ventricles relax and fill with blood from the atria. During systole, the atria relax and collect blood from the lungs and body, while the ventricles contract and pump blood out of the heart. This coordinated action ensures efficient blood flow throughout the body.
The path of blood flow during these phases starts with blood flowing into the relaxed atria from the veins, which are higher in pressure. The blood then moves passively from the atria into the ventricles due to the rising pressure. During atrial systole, the pressure within the atria rises further, pumping blood into the ventricles. Finally, during ventricular systole, blood is pumped out of the heart into the pulmonary trunk from the right ventricle and into the aorta from the left ventricle, ensuring blood reaches throughout the body.