The Cardiac Cycle

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I am unsure about the underlined parts of the cardiac cycle. I was taught that the cardiac cycle started when the blood flowed into the atrium, but wouldn't there be a period when both artia and ventricles are at diastole simultaneously?

For the second underlined part I was taught and read that 70% of blood flows unimpeded into the ventricles during diastole. However, they never mentioned how they shut for when they opened again during atrial systole. So, I used what I knew to make a guess, but I am unsure.

1. At the start of the cardiac cycle the atria and ventricles are relaxed. atrial and ventricular diastole.
2. Both atria fill with blood from the pulmonary vein and vena cava.
3. Blood travels passively down into the ventricles filling them to 70% of their capacity, pressure in the ventricles increase above the pressure of the atria closing the AV valves.
4. Both atria contract and blood flows down through the atrioventricular vales into the ventricles (to 100% their capacity). The AV valves open due to an increase in pressure in the both atria. Atrial Systole
5. The Atria relax. Atrial Diastole
6. The AV valves close due to the ventricles having a higher pressure than both atria, preventing back flow and creating the heart beat sound “lub”.
7. The ventricle walls contract from the apex of the heart upwards increasing the pressure in the ventricles forcing the semi-lunar valves to open. This forces blood to flow up into the pulmonary artery and aorta. Ventricular systole
8. The ventricles relax. Ventricular diastole
9. Pressure in the ventricles fall below that in both atria.
10. High blood pressure in the aorta and pulmonary artery rise causing the semi-lunar valves to shut preventing back flow. This produces the second heart sound “dub”.
11. Blood flows once more from the vena cava and pulmonary veins into the left and right atrium, starting the whole cycle again.
 

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  • #2
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800px-2027_Phases_of_the_Cardiac_Cycle.jpg

Source: Wikipedia
At the start of the cardiac cycle the atria and ventricles are relaxed. atrial and ventricular diastole.
You are referring to Early Ventricular Diastole as in the above diagram. #1 and #2 are related, in the sense that atria start getting filled in #1 itself. You cannot clearly distinguish where #1 ends and #2 starts.

In #2, also include the coronary sinus.
pressure in the ventricles increase above the pressure of the atria closing the AV valves
I cannot confirm this, because I haven't read it before. I believe before the valve closes, the systolic of atria starts. Some doctor-cum-professor can confirm this.
 

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  • #3
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You are referring to Early Ventricular Diastole as in the above diagram. #1 and #2 are related, in the sense that atria start getting filled in #1 itself. You cannot clearly distinguish where #1 ends and #2 starts.

In #2, also include the coronary sinus.
Thanks for clearing it up for me.
 
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