Describe the phases of the cardiac cycle (atrial systole, ventricular systole, general diastole) and define systole.

3. Describe what happens in the following phases of a cardiac cycle.

a) Atrial systole
During atrial systole, the atria contract, pushing the remaining blood into the ventricles. This accounts for about 20-30% of ventricular filling.

b) Ventricular systole
During ventricular systole, the ventricles contract. First, the atrioventricular valves close, then the semilunar valves open, and blood is ejected from the ventricles into the aorta and pulmonary artery.

c) General diastole
During general diastole, all four chambers of the heart are relaxed. Blood flows from the atria into the ventricles, filling them passively.

4. Define the following words:

a) Systole
Systole refers to the phase of the cardiac cycle when the heart muscle contracts and pumps blood from the chambers into the arteries.