The cardiac cycle

• what is atrial systole?

  • contraction of cardiac muscle in atria
• what is ventricular systole?

  • cardiac muscle in ventricles contracting
• what happens to pressure in atrial and ventricular systole?

  • pressure inside heart increases dramatically and blood is forced out of the right side of the heart to the lungs and from the left side to the main body circulation, the volume and pressure of blood in the heart are low at the end of systole, and the blood pressure in arteries is at a maximum
• what is diastole?

  • relaxation of cardiac muscle
  • takes place simultaneously in all 4 chambers of the heart
  • atria and then ventricles fill with blood, the volume and pressure of the blood in the heart build as the heart fills, but the pressure in the arteries is at a maximum
• in which direction does blood flow?

  from a region of high hydrostatic pressure to a region of lower hydrostatic pressure
• what are valves designed to do?

  • designed so they open whenever the blood pressure either side favours the movement in the desired direction
  • stop the back flow of blood
• when is the atrioventricular valve open?

  diastole and atrial systole (closed in ventricular systole)

  • makes ‘lub’ sound when closes
• when is the semi-lunar valve open?

  ventricular systole (closed during diastole and atrial systole)

  • makes ‘dub’ sound when closes
• label the diagram

  A) aortic pressure

  B) atrial pressure

  C) ventricular pressure

  D) ventricular volume

  E) ECG

  F) diastole

  G) ventricular systole

  H) atrial systole

  I) atrioventricular valve closes

  J) semilunar valve closes

  K) semilunar valve opens

  L) atrioventricular valve opens

  
• The right side of the heart receives deoxygenated blood from the vena cavae via the superior and inferior vena cavae. It then passes this on to the lungs where carbon dioxide diffuses out of the blood and oxygen diffuses into the blood. Oxygenated blood returns to the left side of the heart via pulmonary veins. From here it is passed onto the rest of the body via the aorta.
• what can cause hydrostatic pressure to increase?

  • contraction as it reduces the volume
  • more blood entering
• what can cause hydrostatic pressure to decrease?

  • relaxation - increases the volume, elastic recoil (walls of vessel or chamber return to full size)
  • blood leaving
• what are the changes in atrial pressure?

  • blood entering atria during atrial, ventricular and diastole
  • atria contracts during atrial systole but not ventricular or diastole
  • blood is leaving atria during atrial systole and diastole but not ventricular
  • AV valve is open during atrial systole and diastole, closed during ventricular
  • SL valve open during ventricular, closed during atrial and diastol
• what is the pressure changes of the atria?

  • atrial systole - increases due to contracting, decreases due to blood leaving
  • ventricular systole - decreases due to relaxing, increases due to blood entering
  • diastole - decreases due to blood leaving, increases due to blood entering
• during ventricular systole the atrial pressure decreases bellow ventricular pressure as atria are relaxing, causing the atrioventricular valve to close
• during diastole the ventricles are now relaxing, so atrial pressure becomes higher than ventricular pressure, causing atrioventricular valve to open
• what are the changes is ventricular pressure?

  • blood entering ventricle during atrial systole and diastole, not ventricular systole
  • ventricles contract during ventricular systole only
  • blood leaving ventricles during ventricular systole only
  • AV valve open during atrial systole and diastole and closed during ventricular systole
  • SL open during ventricular systole and closed during atrial and diastole
• what are the pressure changes in the ventricles?

  • atrial systole - increases due to blood entering
  • ventricular systole - increases due to contracting, decreases due to blood leaving
  • diastole - decreases due to blood leaving, increase due to blood entering
• during ventricular systole, ventricles contract with more force than atria, so pressure increases much more than in atria - causing atrioventricular valve to close

  ventricular pressure is greater than aortic pressure, so semilunar valve closes
• during diastole, aortic pressure is now higher than ventricular pressure, so semi-lunar valve closes

  atrial pressure becomes higher than ventricular pressure, which causes the atrioventricular valve to open
• what are the changes to ventricular volume?

  • blood entering ventricles during atrial and diastole, but not during ventricular systole
  • volume increases during atrial systole as blood is forced into ventricles due to atria contracting
  • volume decreases during ventricular systole as ventricles are contracting forcing blood out of ventricles (AV closed)
  • volume increases due to blood entering ventricles slowly from atria
• what are the changes to aortic pressure?

  • blood enters aorta during ventricular systole but not during atrial or diastole
  • AV valve is open during atrial and diastole but not during ventricular
  • SL valve is open during ventricular but not during atrial pr diastole
• atria contraction has no effect on the SL valve which remains closed so aortic pressure won't be affected - pressure remains constant in arteries and aorta as it is maintained by the smooth muscle, elastic tissue and narrow lumen of blood vessel
• • once pressure is greater in ventricles than aorta the semi-lunar valve opens
  • blood entering increases aortic pressure
  • pressure difference flips and aortic pressure is greater than ventricular pressure closing the semi-lunar valve
• how do you calculate heart rate?

  heart rate (bpm) = (number of beats/time in seconds) * 60
• what is cardiac output?

  the total volume of blood pumped by the heart in one minute
• what is stroke volume?

  the volume of blood pumped in one beat of the heart
• how do you calculate cardiac output?

  cardiac output (cm3 min-1) = heart rate (beats min-1) * stroke volume (cm3 beat-1)