![]() ![]() ![]() The atrioventricular valves close due to the pressure in the ventricles becoming greater than the pressure in the atria (backflow to the atria is prevented).The chamber volume of the ventricles decreases so pressure increases. ![]() The atria are now relaxed, they’ve done their job.Next we need to get the blood out of the ventricles through the aorta and pulmonary artery. Now all the blood is in the ventricles we’re moving in the right direction. The pressure and chamber volume of the ventricles increase slightly as they fill.Blood is forced through the open atrioventricular valves into the ventricles.The chamber volume of the atria decreases so pressure increases.So first of all the blood needs squeezing from the atria to the ventricles, and here’s how it happens: We learnt in the last article that blood enters the heart through the vena cava and pulmonary vein, and ends up in the atria. Let’s have a look at each stage of the cardiac cycle. If the atria or ventricles are in systole it means they are contracting, and if they are in diastole it means they are relaxing. Two important words you need to know before we start are systole and diastole. It’s fairly complicated, but broken down into steps it makes sense if you think about the direction blood travels through the heart. The cardiac cycle is the sequence of contraction and relaxation that the heart goes through continuously to keep blood pumping around the body. ![]()
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