[Biology][Practical-10] Cardiac Cycle Questions


  • pressure = force/area

  • The blood goes from atrium to ventricle during atrial systole

  • The blood goes into the atrium and ventricle during diastole

  • The aortic valve is open during ventricular systole

  • What happens during arital systole?


  • What happens during ventricular systole?


  • The second heart sound occurs when the aortic valve closes

  • What happens during diastole?


  • The blood goes from ventricle to aorta during ventricular systole

  • The first heart sound occurs when the aortic valve opens

  • The conduction system of the heart is made of:

  1. The SA node (sinoatrial)
  2. The AV node (Atrioventricular)
  3. Atrioventricular bundle or “Bundle of His”
  4. Purkinje fibers
  • What is the SA node? The heart’s natural pacemaker

  • The SA node is located in the right atrium

  • What is the AV node? It delays the electrical impulses generated by the SA node, allowing the atria time to contract and pump blood into the ventricles. The AV node then conducts the electrical impulses to the ventricles, causing them to contract and pump blood out of the heart.

  • The AV node is located in the lower part of the right atrium

  • Complete the following sentence:

    • The bundle of His is a bundle of specialized cardiac muscle fibers that carry electrical impulses from the AV node to the ventricles through the Purkinje fibers
    • The Purkinje fibers are specialized cardiac muscle fibers responsible for conducting electrical impulses from the bundle of His to the ventricles.

Complete the following sentences:

  • 1 refers to the closing of the AV valve
  • 4 refers to the opening of the AV valve
  • 2 refers to the opening of the aortic valve
  • 3 refers to the closing of the aortic valve

Complete the following sentences:

  • A refers to the atrial contraction

  • D refers to the isovolumetric relaxation

  • E refers to the atrial filing

  • F refers to the ventricular filing

  • B refers to the isovolumetric contraction

  • C defers to the ventricular ejection


but doesnt lub sound (both heart sounds) take place when a valve closes, so shouldnt answer be when atrioventricular valve or semilunar valve closes ?


There are two sounds: lub dub. When the AV valves close, a “lub” sound is heard. That is also when the aortic valve opens. When the valves in the pulmonary and aortic arteries leaving the heart close, a “dub” sound is heard.


yea i got that part was just checking which was more accurate, thanks for replying!

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But still I don’t think the AV valve closes at the same time as the aortic valve opens, does it? If you look at the diagram, it opens a bit after AV valve closes.

Hey! In the cardiac cycle, the atrioventricular (AV) valves and the semilunar valves (aortic and pulmonary valves) do not open and close simultaneously. Here’s a simplified sequence of events in the cardiac cycle:

  1. Diastole (Relaxation Phase):
  • Both atria and ventricles are relaxed.
  • AV valves (tricuspid and mitral/bicuspid) are open.
  • Semilunar valves (aortic and pulmonary) are closed.
  • Blood flows from atria to ventricles.
  1. Atrial Systole (Atrial Contraction):
  • Atria contract, pushing the remaining blood into the ventricles.
  1. Ventricular Systole (Ventricular Contraction):
  • At the beginning, as the ventricles start to contract, the pressure rises, which causes the AV valves to close (“lub” sound of the heartbeat).
  • Once the ventricular pressure exceeds the pressure in the aorta and pulmonary artery, the semilunar valves open, allowing blood to eject out of the ventricles.
  • There’s a brief period between the closure of the AV valves and the opening of the semilunar valves known as isovolumetric contraction, where all valves are closed, and the ventricles are contracting but not ejecting blood.
  1. Isovolumetric Relaxation:
  • After ventricular contraction, the ventricles begin to relax. The fall in ventricular pressure causes the semilunar valves to close (“dub” sound of the heartbeat).
  • For a brief moment, all valves are closed again, which is the isovolumetric relaxation phase.
  • When the pressure in the ventricles falls below that of the atria, the AV valves open, signaling the start of a new cardiac cycle.