The Cardiac Cyle

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  • Sequence of Contraction
    • 1.Filling Phase (Diastole)
      • While both the Atria and the Ventricles are relaxing the internal volume increases and blood flows into the heart from teh major Veins. The Blood flows into the Atria, then through the open atrioventricular valves and into the Ventricles
    • 2.Atrial Contraction (Systole)
      • The Heart beat starts when the Atria contract. Both right and Left Atria contract together. The small increase in pressure helps to push the blood into the ventricles. This stretches the walls of the ventricles to ensure they are full of blood. Once the ventricles are full they start to contract. Blood fills the atrioventricular valve flaps making them shut.
    • 3. Ventricular Contraction (Ventricular Systole)
      • Now there is a short period where all 4 valves are shut. The walls of the ventricles contract. This raises the pressure in the ventricles very quickly. The contraction starts ar the base of the heart to push the blood up. The semilunar valves open and blood is pushed out. Then the ventricle walls relax allow it to start over
    • The Cardiac Cycle
      • How Valves Work
        • Arioventricular Valves
          • When the ventricular walls relax and recoil after contracting, the pressure in the ventricles drop below the pressure in teh atria, this causes the atrioventricular valves to open.
            • Blood entering the heart flows straight through the atria and into the ventricles. The pressure in the atria and the ventricles slowly rises as they fill with blood. The valves remain open while the atria contract.
              • As the Ventricles contract, the pressure of the blood in the ventricles rises. When the pressure rises above that in the Atria, the blood starts to move upwards.
                • This movement fills the valve pockets and keeps them closed. this prevents the blood flowing back
        • Semilunar Valves
          • When the ventricles start to contract, the pressure in the major arteries is higher than the pressure in the ventricles. This means that the semilunar valves are closed. As the ventricles contract the pressure inside rises quickly because the blood cannot escape.
            • Once the Pressure in the Ventricels rises aboce the pressure in the aorta and pulmonary arteries, the Semilunar valves are pushed open. The blood is under very high presure so it is forces out of the ventricles
      • The Sound of the Heart
        • The 1st sound, lub, is made by the atrioventricular valves closing as the ventricles contract
        • The 2nd sound, dub, is the semilunar valves closng as the ventricles relax
      • Control of the Cardiac Cycle
        • Fibrillation
          • The Cardiac muscle initiates its own contraction, it is MYOGENIC it should contract and relax rythmically
            • The muscles from the atria and the ventricles each have their own frequency of contraction. This property can cause inefficient pumping. If the contraction of the chambers are not synchronised.
        • Electrocardiograms (ECG)
          • Used to monitor electrical activity of the heart.
          • The trace of a healthy person has a particular shape, it consists of a series of waves P, Q, R , S, T
            • Wave P shows the excitation of the atria.
            • QRS indicates the excitation of the Ventricles.
            • T shows Diastole


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