Valves are needed to prevent blood flowing backwards into the heart.
To prevent backflow of blood into the Ventricles.
the function of the semilunar valves are that they provied the lungs with glucose and oxygen.
The tendinous cords are located in the ventricles. The function of the tendinous cords that are attached to the bicuspid and tricuspid valves is to connect the atrio-ventricular valves to the papillary muscles.
When the ventricles are relaxed, the semilunar valves are closed, while the atrioventricular (AV) valves are open. This allows blood to flow from the atria into the ventricles. The closure of the semilunar valves prevents backflow of blood from the arteries into the ventricles during this phase.
Pulmonary and aortic valves are semilunar valves having three semilunar cusps each. these valves open with the free ends facing the vessels when the heart contracts and closes when heart relaxes thus preventing regurgitation
There are no valves between the atria. The valves between the atria and ventricles close when the ventricles contract.
Both AV valves, the bicuspid and tricuspid, (separating the ventricles from the atria) prevent blood from flowing back into the atria when the ventricles contract. Both the semilunar valves (separating the arteries from the ventricles) prevent blood from flowing back from the arteries once it has been pumped out of he ventricles, and thus, out of the heart. The difference is that the AV valves are contracted when they are CLOSED, but the semilunar valves are contracted when OPEN. Otherwise, I can't think of another major job besides preventing backflow.
AV valves stop the back flow of blood from ventricles to atrium during ventricular systole
As the ventricles of the heart contract the pressure in the ventricles rises beyond that of the atria. This pressure differential causes the AV valves to shut.
Atrio-ventricular valves
ventricles