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Leaving certificate biology

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  1. Ecology theory
    5 Topics
    |
    1 Quiz
  2. Unit 1
    Nutrient recycling
    4 Topics
    |
    1 Quiz
  3. Ecological relationships and population dynamics
    2 Topics
  4. Human impact on the ecosystem
    2 Topics
  5. Study of a grassland ecosystem
    3 Topics
  6. Responses in the Flowering Plant
    4 Topics
    |
    1 Quiz
  7. Unit 3
    Sexual reproduction in the flowering plant
    1 Topic
  8. The human reproductive system
    3 Topics
  9. The menstrual cycle
    2 Topics
  10. Pregnancy
    2 Topics
  11. The circulatory system
    4 Topics
  12. Blood
    5 Topics
  13. The heart
    5 Topics
Lesson 13, Topic 2
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The cardiac cycle

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The cardiac cycle

  • Systole: the contraction of heart muscle 

  • Diastole: the relaxation of heart muscle

Summary of the path of blood in the cardiac cycle

  1. Deoxygenated blood from the body enters the right atrium via the superior and inferior vena cava

  2. When the right atrium contracts (atrial systole) blood is pumped through the tricuspid valve into the relaxed right ventricle

  3. The right ventricle contracts pumping blood through the pulmonary semilunr valve into the left and right pulmonary arteries which carry deoxygenated blood to the lungs

  4. The left atrium receives oxygenated blood from the pulmonary veins

  5. The left atrium contracts pumping blood through the bicuspid valve into the relaxed left ventricle

  6. The left ventricle contracts pumping blood through the aortic semilunar valve and through the aorta to the body

How the heart beat is controlled

  • The pacemaker (SA node) is located in the right atrium

  • Its function is to control the rate of the heartbeat

  • The pacemaker sends out electrical pulses about every 0.8 seconds 

  • The electrical pulses cause the atria to contract

  • The AV node is located in the septum between right atrium and right ventricle

  • When an electrical pulse reaches the A-V node the pulse is strengthened and sent down special tissue located  in the septum 

  • The electrical impulses pass out along specialized fibers and cause the walls of the ventricles to contract