Which events occur during the atrial contraction and ventricular filling phase of the cardiac cycle?

• A. The atria contract, pushing blood into the ventricles.
• B. The ventricles contract, ejecting blood into the aorta and pulmonary artery.
• C. The semilunar valves open to allow blood flow into the ventricles.
• D. The atrioventricular valves close to prevent backflow into the atria.

Answer: (A)

Verified step by step guidance

1. Understand the cardiac cycle phases: The cardiac cycle consists of several phases, including atrial contraction, ventricular filling, ventricular contraction, and relaxation.
2. Focus on atrial contraction and ventricular filling: During this phase, the atria contract to push blood into the ventricles, which are relaxed and filling with blood.
3. Identify valve actions: The atrioventricular (AV) valves (tricuspid and mitral) are open during atrial contraction to allow blood flow from the atria to the ventricles.
4. Recognize the role of semilunar valves: The semilunar valves (aortic and pulmonary) remain closed during atrial contraction and ventricular filling to prevent blood from flowing back into the ventricles from the arteries.
5. Note the transition to ventricular contraction: After the atria contract and the ventricles are filled, the ventricles will begin to contract, leading to the closure of the AV valves to prevent backflow into the atria.