Unit 1 Section 5.2

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  • Heart Basics
    • External and Internal Structure of the Heart
      • Heart Valves
        • the atrioventricular valves
          • link the atria to the ventricles
        • Semi lunar Valves
          • link the ventricles to the pulmonary artery and aorta
          • stop blood flowing the wrong way
            • the atrioventricular valves
              • link the atria to the ventricles
        • the valves only open one way - whether they're open or closed depends on the relative pressure of the heart chambers.
        • If There's higher pressure behind a valve, its forced open. if pressure is higher in front of the valve its forced shut
    • Thickness of heart Chamber walls
      • the heart is mainly cardiac muscle. when its contracts it creates high pressure - enough to force blood all the way around the body
      • each of the four chambers of the heart has a different function
        • the more work that a heart chamber has to do, the more muscle it needs - so the thicker the wall is
        • the left ventricle of the heart has thicker, more muscular walls than the right ventricle
          • because it needs to contract powerfully to pump blood all the way round the body
            • the right side only needs to get  blood to the lungs which are nearby.
        • the ventricles have thicker walls than the atria, because they have to push blood out of the heart whereas the atria just need to push blood a short distance into the ventricles
    • The Cardiac Cycle
      • is an ongoing sequence of contraction and relaxation of the atria and ventricles that keeps blood continuously circulating round the body
      • the volume of the atria and ventricles changes as they contract and relax, altering the pressure in each chamber
      • this causes valves to open and close which directs the blood flow through the heart. the cardiac cycle can be simplified into 3 stages
        • 1. VENTRICLES RELAX AND ATRIA CONTRACTS
        • 2. VENTRICLES CONTRACT  AND THE ATRIA RELAX
        • 3. VENTRICLES RELAX AND THE ATRIA RELAX

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