cardiac cycle

• arteries and veins

  • arteries have thick walls and a pulse to carry oxygenated blood away from the heart
  • veins have thin walls and valves to carry deoxygenated blood towards the heart
• Cardiac cycle


  1. Diastole: Atria and ventricles are relaxed, AV valves are open, deoxygenated blood flows into right atrium

  2. Systole: Right atrium contracts, empties into right ventricle, right ventricle contracts, forcing blood out along pulmonary artery, PA valve closes to prevent backflow

  3. Blood flows through pulmonary arteries to lungs, picks up O2, CO2 removed, oxygenated blood returns to left atrium

  4. Left atrium empties into left ventricle, left ventricle contracts, forcing blood out along aorta, AV valves close to prevent backflow
• Diastole


  1. Atria and ventricles are relaxed

  2. Atrioventricular valves are open
• Deoxygenated blood


  Flows into the right atrium from the vena cava
• Diastole


  Open av valves allow blood to pass through ventricles
• Systole


  Right atrium begins to contract, emptying its contents into the right ventricle
• Systole


  Right ventricle contracts, forcing blood out of the heart along the pulmonary artery towards the lungs
• Systole


  Right av valve is forced closed which prevents the backflow of blood to the lungs where gas exchange occurs
• Gas exchange


  Blood picks up oxygen and carbon dioxide is removed before the blood returns to the left atrium through the pulmonary veins
• Diastole


  Oxygenated blood from pulmonary veins fill the left atrium
• Systole


  Left atrium empties into the left ventricle
• Systole


  Left ventricle contracts, forcing av valves closed
• when you exercise, blood is directed towards the working muscles, this is achieved by vasoconstriction and vasodilation which changes the internal diameter of the arteries that supply blood to the working muscles
• cardiac output = stroke volume x heart rate