Questions: 2:51PM Sun Nov 3 AA ezto.mheducation.com Human Anatomy and Physiology 2 with Lab Question 25 - Chapter 19 Assignment (i) Saved 25 Part 1 of 5 0.31 points eBook Print References The ventricles contract. The atrioventricular valves close. The semilunar valves open. The ventricles relax. Mc Graw Prev 25 26 27 29 of 32

The sequence of events described in the question pertains to the cardiac cycle, specifically the phases of the heart's pumping action. Here's a breakdown of the events:

1. The ventricles contract: This phase is known as ventricular systole. During this phase, the ventricles contract to pump blood out of the heart.

2. The atrioventricular valves close: As the ventricles contract, the pressure inside them increases, causing the atrioventricular (AV) valves (the tricuspid and mitral valves) to close. This prevents the backflow of blood into the atria.

3. The semilunar valves open: With continued contraction, the pressure in the ventricles exceeds the pressure in the arteries (aorta and pulmonary artery), causing the semilunar valves (aortic and pulmonary valves) to open. This allows blood to be ejected from the heart into the systemic and pulmonary circulation.

4. The ventricles relax: This phase is known as ventricular diastole. After the blood is ejected, the ventricles relax, and the pressure within them falls. This leads to the closing of the semilunar valves to prevent backflow of blood from the arteries into the ventricles.

In summary, the sequence of events in the cardiac cycle is as follows: the ventricles contract, the atrioventricular valves close, the semilunar valves open, and then the ventricles relax.