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    Ocr biology as - i need to know everything on the heart >

    thanks in advance

    Structure of the heart:
    Probably best to look at a diagram for this but you need to know the basics ie. position of the atria, ventricles, names of the valves, names of the blood vessels leading into and out of the heart.

    Movement of blood:
    (Can be in any order as it is a circle)
    Again, this is easier to understand if drawn in a diagram.
    - deoxygenated blood enters right atrium from vena cava
    - deoxygenated blood taken to lungs in pulmonary artery from right ventricle
    - oxygenated blood returns to left atrium in pulmonary vein
    - oxygenated blood delivered to body in aorta from left ventricle

    Walls of the ventricles are thicker than walls of atria as they pump blood into the arteries which requires more force than pumping blood into the ventricles. The walls of the left ventricle are much thicker than the walls of the right ventricle because blood from the left ventricle needs to be pumped around the whole body whereas the right ventricle only pumps blood to the lungs which are relatively close to the heart.

    Cardiac cycle:

    - blood enters the heart from the vena cava (right hand side) and the pulmonary vein (left hand side)
    - semi lunar valves (base of the arteries leading out of the heart) are closed
    - atrioventricular valves (between atria and ventricles) are open

    Atrial systole:
    - aria contract forcing blood into ventricles
    - semi lunar valves are closed
    - atrioventricular valves are open

    Ventricular systole:
    - ventricles contract from the bottom up, forcing blood into arteries
    - when pressure in ventricles is greater than pressure in arteries, semi lunar valves open
    - when pressure in ventricles is greater than pressure in atria, atrioventricular valves close

    Control of cardiac cycle:
    - cardiac muscle is myogenic meaning it can initiate its own contraction
    - sinoatrial node (SAN) initiates a wave of excitation which spreads across atria causing them to contract
    - atrioventricular node (AVN) at the top of the septum is the only place at the base of the atria that is able to conduct the wave
    - the AVN delays the impulse to allow the atria to fully contact and for blood to flow into ventricles
    - wave is then carried by Purkyne tissue down the septum to the apex (bottom) of the heart
    - the wave then spreads up the ventricle walls causing them to contract from the bottom up so blood is forced into arteries at the top of the heart

    Have a look at some diagrams of electrocardiograms to see the differences between normal and abnormal heart activity.

    Hope this helped
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