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    Could someone explain to me what happens during diastole; the SNAB textbook isn't making much sense to me.

    Thank you very much!

    Both the atria and ventricles relax, the semi-lunar valves close and pressure drops drawing blood back in through the pulmonary veins into the atria so that the whole process can start again.

    Boom! Recited that on the Rum as well.

    I don't know if this will be too confusing but there is ventricular systole/diastole and atrial systole/diastole, and I think to an extent atrial systole overlaps with ventricular diastole.

    The cardiac cycle starting at ventricular systole:

    - Vs contract, mitral and tricuspid valves close (LUB) no blood movement because all valves are closed (isovolumetric contraction)

    - Aortic and pulmonary (semilunar) valves open, blood leaves Vs (ejection)

    - Ventricles relax, closure of semilunar valves (DUB) (all valves closed = isovolumetric relaxation)

    - Mitral and tricuspid valves open

    - Blood flows from atria into ventricles passively (full cardiac diastole: both atria and ventricles are relaxed)

    - Atria contract to push a little more blood into the ventricles (atrial systole BUT still ventricular diastole, I believe)
    (This is actually the electrical beginning of the heart cycle, with the SA node firing off)

    - Mitral and tricuspid valves close with ventricular contraction...
    - Etc (back around again)

    Right the BLUE is diastole, the PURPLE is kind-of diastole (the atria are in systole, but ventricles in diastole)

    EDIT: Ahh SNAB is A-level biology?
    Then probably the answer you need is: ventricles relax, semilunar valves close, tricuspid and bicuspid valves open, blood flows from atria into ventricles.

    There are just three basic stages

    1:Atrial systole, Ventricular diastole
    This is when the atria contract (systole), and all the blood that was in the atria is transferred to the ventricle. This flow of blood pushes open the AV valves allowing the ventricle to fill up.

    2:Atrial diastole, Ventricular systole
    This is when the atria is now relaxed (diastole) and the ventricles contract forcing blood to push against the semi lunar valves, forcing them to open and allow the blood to pass through. At this stage the AV valves are closed so no blood is transferred back to the atria.

    3: Atrial diastole,Ventricular diastole
    This when both the atria and ventricle is relaxed waiting for the cycle to repeat again

    If you want more info use the CGP biology textbook AS
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