Describe the Cardiac Cycle and Relate the Structure and Operation of the Mammalian Circulatory System to Its Function

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‘Describe the cardiac cycle and relate the structure and operation of the mammalian circulatory system to its function’ The cardiac cycle is an repeating sequence of contraction and relaxation of the atria and ventricles. The cardiac cycle allows for blood to be continuously transported around the body via the circulatory system. The features of the heart and the circulatory system are adapted in order for their functions to be carried out correctly. The first stage of the cardiac cycle is atrial systole/ventricular diastole. The atria contract, which decreases the volume of the atrium and increases the pressure within it. The atrioventricular valves are opened and blood is pushed past the bicuspid valve to fill the ventricles. This increases the pressure and volume of the ventricles. There are several parts of the heart that are adapted for this stage of the cardiac cycle. The ventricles have thicker walls than the atria. This allows them to perform their function of pushing blood out of the heart. Atria do not need as thick walls because they only have to push blood into the ventricles. The atrioventricular (AV) valves connect the atria and the ventricles. These valves are opened and closed depending on pressure differences between the atria and ventricles. They prevent the backflow of blood from the ventricles to the aorta in the second stage of the cardiac cycle. The second stage of the cardiac cycle is ventricular systole/atrial diastole. The atria relax and the ventricles contract. This decreases the volume of the ventricles and increases the pressure within them. The increase in pressure forces the AV valves to close, which prevents the flow of blood back into the heart. The pressure in the ventricles is higher than the pressure in the aorta and pulmonary artery. This forces the semilunar valves open and blood is pushed into the aorta and pulmonary

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