The Heart

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  • The Heart
    • Internally
      • septum separates deoxgynated and oxygenated blood
        • deoxygenated blood goes to lungs, oxygenated to the body
      • 4 chambers - 2 artia and 2 ventricles
      • blood flows from the atria, down through the atrioventricular valves and into the ventricles
        • when the ventricles contract the valves fill with blood and remain closed
      • Valves - thin flaps of tissue that ensure blood flows in the right direction around the heart
      • Tendinous Cords - attach valves to the walls of the ventricle and prevent valves from turning inside out
      • When the ventricles contract they force the blood into the aorta/pulmonary artery to the body/lungs
        • At the base of the major arteries are the semilunar valves - they prevent blood from returning to the heart as the ventricles relax
      • Semilunar Valves
        • ventricles start to contract, pressure in major arteries is higher than that in the ventricles, so the valves are closed
          • As the ventricles contract their pressure rises very quickly as the blood cannot escape
            • when pressure reaches above that in the arteries the valves are forced open
              • blood is at very high pressure so is forced out in a powerful spurt
                • as the ventricle walls finish contracting the muscle begins to relax. Elastic tissue in the walls of the ventricles recoils - stretching the wall out
                  • the pressure drops below that in the major arteries and as blood attempts to flow back into the ventricles, collecting in the pockets of the valves, so the valves are forced shut
      • Artrioventricular Valves
        • when the ventricular walls relax and recoil the pressure in the ventricles drops below the pressure in the artia, so the valves open
          • blood entering the heart flows straight through the artia and into the ventricles, pressure in both rises slowly
            • the valves remain open whilst the atria contract but as the ventricles begin to contract the pressure of the blood in them rises and the blood starts to move upwards
              • this movement fills the valve pockets and foreces them closed so that the blood cannot move into the atria
    • Externally
      • dark red muscle, which feels firm, surrounds the ventricles
      • slightly off centre to the left of the chest cavity
      • coronary arteries lie over the surface of the heart - provide it with oxygen
    • Pressure
      • the heart squeezes the blood, putting it under pressure and forcing the blood along the arteries
        • the higher the pressure created in the heart, the further the blood is pushed
      • Ventricular Pressure
        • Much thicker walls than atria enables ventricles to pump blood out of heart around lungs/body
        • Left Ventricle - can be 2/3 times thicker than right ventricle as pressure must be high enough to push blood around body and overcome the resistance of the systematic circulation
        • Right Ventricle - thinner walls than left ventricle as only pumps blood to lungs. Pressure cannot be high or capillaries could burst
      • Atrial Pressure
        • the muscle in the walls of the atria is very thin as they only have to create enough pressure for the blood to get to the ventricles
    • Sound of the heart
      • lub-dup sound made by the valves closing
      • lub - atrioventricular valves closing as the ventricles start to contract - loader as the valves snap shut when blood accumulates
      • dup - made by semilunar valves closing as the ventricles start to relax

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