Two phases of the beating of the heart = contraction (systole) and relaxation (diastole).
Contraction occurs separately in atria and ventricles.
Relaxation of the heart (diastole)
Blood returns to atria of heart through pulmonary vein and vena cava.
As atria fill, blood pressure in them rises, pushes atrioventricular valves open, blood passes into ventricles.
Atria and ventricles are both relaxed at this stage.
Relaxation of ventricle wall = pressure within ventricle reduced so is lower than in aorta and pulmonary artery, so semi-lunar valves close.
Contraction of the atria (atrial systole)
Muscle of atrial wall contracts - forces remaining blood into ventricles, ventricle wall remains relaxed.
Contraction of ventricles
After ventricles are filled with blood, walls contract simultaneously.
Increases blood pressure within them, forces atrioventricular valves shut (prevents backflow of blood).
Pressure rises further, forcing semi-lunar valves open, pushing blood into pulmonary artery and aorta.
Valves in control of blood flow
Pressure created by heart muscle keeps blood flowing in the right direction.
Blood moves from region of higher pressure to lower pressure.
Valves in cardiovascular system are designed to open whenever…