When the semilunar valves are open, which of the following are occurring? (1) coronary arteries fill (2) AV valves are closed (3) ventricles are in systole (4) ventricles are in diastole (5) blood enters aorta (6) blood enters pulmonary arteries (7) atria contract a. 2, 3, 5, 6, b. 1, 2, 3, 7, c. 1, 3, 5, 6, d. 2, 4, 5, 7.

Video transcript

Hi, everybody. Welcome back. Let's look at our next question. At which stage of the cardiac cycle are the two atria filling up with blood? A atrial systole B, atrial diastole, C ventricle cysto or D, both A and B. Well, to think this through, it's helpful to remember what is going on in sly and diastole in Sicily, the heart muscle is contracting and in dias it is relaxing. And the way I like to remember that is I think of cyle, it begins with si think of S as looking like a squeezed muscle, squeezed, contracted muscle and diastole, which begins with D I think of the uh circle and the letter D as being relaxed and open. So that's what helps me remember this difference between the two. So at which stage of this cardiac cycle will the atria be filling up with blood? Well, to be filling up, you'd want them to be relaxed to allow blood to flow in. And indeed, our answer is choice B atrial dias during atrial diace, the blood flows into the relaxed atria from the veins just by pressure, differential, lower pressure in the atrium at this stage. The A V valves are also open. And so blood is flowing into the ventricles as well as the atria. When we look at our other answer, choices during choice, a atrial cysto, that's after the blood has flowed into the atria. And now the atria contract closed, squeezing all the blood that was in there into the ventricles. So in atrial cysto, the atria are emptying. So that's not our correct answer. And therefore, of course, we also rule out choice d both A and B and then finally to ac in ventricle cysto. So the in ventricular cysto, the ventricle is contracting, this has two phases. The first being the isovolumetric contraction, isovolumetric, you think of iso meaning same. So at this point, the pressure is increasing in the ventricle, it's a higher pressure than the atrium. So that closes the A V valves. But the pressure in the ventricle is not high enough yet to open the semi lunar valves. So there's no change in the volume of the ventricles because the semi lunar valves exiting the ventricle are still closed. Then in the second phase of ventricular cysto which is ventricular ejection, the pressure builds high enough in the ventricles that the semi lunar valves open and blood is ejected from the ventricles out into the body. So in ventricular ejection, the semi lunar valves are open. So there's two phases to ventricular cyst. But at that point, blood is not filling up in the atrium. That's when blood has filled the ventricles. The atrium is the atria are empty and blood will eventually be ejected from the ventricles. So not the answer we're looking for the stage in the cardiac cycle. When the two atrial are filling up with blood. This choice b atrial diastole. See you in the next video.