The Pathway of Blood (OCR GCSE Physical Education (PE)): Revision Note

The cardiac cycle & the pathway of blood

• The cardiac cycle describes the pathway of blood through the heart and the rest of the body

• Each cardiac cycle contains one cycle of both diastole and systole:

  • Diastole

    • When the chambers of the heart relax and fill with blood

  • Systole

    • When the chambers contract and eject blood from the heart

• Note that during systole the left and right-hand sides of the heart contract at the same time

• The cardiac cycle begins when deoxygenated blood flows through the vena cava and enters the right atrium

  • This blood has come from the body, so the oxygen has been used up by the working muscles and replaced by carbon dioxide

• The right atrium contracts and the deoxygenated blood is forced through the tricuspid valve into the right ventricle 

• The right ventricle contracts and the blood is pushed through the semi-lunar valve into the pulmonary artery 

• The blood travels to the lungs and moves through the capillaries past the alveoli where gaseous exchange takes place and the blood is now oxygenated

• This oxygenated blood then travels back to the heart and enters it through the pulmonary vein to the left atrium 

• The left atrium contracts and forces the blood through the bicuspid valve into the left ventricle 

• The left ventricle contracts and the blood is forced through the semi-lunar valve and out through the aorta 

  • The walls of the left ventricle are thicker to produce a high enough pressure for the blood to travel around the whole body 

• The aorta delivers oxygenated blood to the body and during exercise the working muscles will use some of this oxygenated blood