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    • Thread Starter

    I know when pressure in the ventricles is greater than the atria, blood flow goes towards the atria, the AV valves shut to prevent backflow and SL valves open so the blood flows towards the aorta and pulmonary artery. What after that though?

    i did this last year on edexcel and basically i learnt it like this:

    Phase 1: atrial systole. Blood under low pressure flows into left and right atria from pulmonary veins and vena cava. Pressure from the atria then forces the atrioventricular valves open and blood flows into the ventricles.

    Phase 2: Ventricular Systole. Ventricles contract from the base of the heart upwards increasing the pressure. This pushes the blood up and out through the arteries. This pressure then closes the atrioventricular valves and pevents back flow.

    Phase 3: Diastole. Atria and ventricles relax. Elastic recoil lowers pressure in atria and ventricles. Blood that is under a higher pressure in the arteries is drawn back towards the ventricles closing semi lunar valves to prevent back flow. The coronary arteries fills. Low pressure in the atria helps to draw blood into the heart from the veins.

    That is all i had to learn last year so hope that helps!

    I don't know what exam board you're on, I'm on OCR and we also need to know the electrical coordination. How I learnt the cycle is:

    Atrial diastole: Deoxygenated blood flows into the right atrium from the vena cava. Oxygenated blood flows into the left atrium from the pulmonary vein.

    Atrial systole: An electrical impulse is sent out from the sino-atrial node and spreads across the top of the atria, causing them to contract, increasing the pressure, opening the atrioventricular valves and pushing the blood into the ventricles. The electrical signal then travels to the atrioventricular node where it is momentarily delayed.

    Ventricular systole: The electrical signal travels down the Pukyne fibres to the apex(base) of the heart, it then spreads up the ventricles. The right ventricle contracts, pushing deoxygenated blood through the pulmonary artery to the lungs. The left ventricle builds in pressure and contracts, opening the aortic valves and allowing the oxygenated blood to flow around the body.

    I'm not 100% sure about my spelling, so if I have made a few mistakes I apologise, I advise making sure all my vocabulary is correct before learning it.

    After the blood is traveling up into the pulmonary artery and aorta, diastole happens.
    The heart relaxes, and as the pressure drops in the ventricles, blood starts to fall down the aorta and pulmonary artery, back towards the heart. However, the semi-lunar valves have 'pockets' which when filled with this blood , cause the semi-lunar valves to snap shut. Stopping the backflow of this blood into the heart, then the cardiac cycle repeats.
    • Study Helper

    Study Helper
    1. When both the atria and the ventricles are relaxed, blood flows into the atria from the major veins.
    2. The blood flows through the atrioventricular valves into the ventricles
    3. The atria contract simultaneously, pushing blood into the ventricles
    4. Blood fills the atrioventricular valve, causing them to snap shut and preventing the blood from flowing
    back into the ventricles
    5. When the pressure in the arteries is higher than the pressure in the ventricles, the semilunar valves shut
    6. The walls of the ventricles contract, starting from the bottom
    7. When the pressure in the ventricles is higher than the pressure in the arteries, the semilunar valves is
    pushed open and blood is pushed out of the heart. The contraction only lasts for a short time
    8. The ventricles relax
    9. When the pressure in the ventricles drops to below that of the atria, the atrioventricular valves open
    10. When the pressure in the ventricles drops to below that of the arteries, the semilunar vavles shut again
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