Cardiovascular system

• cardiac output = heart rate x stroke volume
• Pulmonary circulation: vena cava to the right atrium through the tricuspid valve to the right ventricle through pulmonary semilunar valve to the pulmonary artery to the lungs
• Systemic circulation: pulmonary vein to the left atrium through the bicuspid valve to the left ventricle through the aortic semilunar valve to the aorta to the body tissues
• Systole: heart working
• Diastole: heart relaxing
• Atrial systole: blood pumped into ventricles
• Ventricular systole: blood pumped into pulmonary artery and aorta
• Atrial diastole: blood entering the atria via the vena cava and pulmonary vein
• Ventricular diastole: blood entering the ventricles from the atria
• The conduction system: specialised bundles of tissue that transmit the electrical impulse through the heart causing a coordinated contraction
• SA node is located in the wall of the right atrium. It sends impulses across both atria causing atrial systole
• AV node is in the middle wall of the heart between the atria and ventricles. Revives impulses from the SA node, delays it for a moment to allow for atrial systole to finish and sends it down the bundles of HIS
• Bundles of HIS is located in the middle wall of the heart. It transmits impulses to the bottom of the right and left side of the heart.
• Purkinje fibres are located in the walls of ventricles. It causes impulses to penetrate into ventricle walls causing ventricular systole.
• Cardiac cycle: the contracting of the cardiac muscle and the movement of blood through the chambers.
• Diastole takes 0.5 seconds for chambers to fill with blood.
• Systole takes 0.3 seconds for blood to be forced out
• Diastole:

  • no electrical impulse
  • mad the atria and ventricles relax they expand drawing blood into the atria
  • the pressure in the atria increases opening AV valves
  • blood passively enters the ventricles
  • SL valves are closed to prevent blood from leaving the heart
• Atrial systole:

  • the atria contract, forcing remaining blood into the ventricles
• Ventricular systole:

  • the ventricles contract increases the pressure closing the AV valves to prevent back flow into the atria
  • SL valves are forced open as blood is ejected from the ventricles into the aorta and pulmonary artery
• Conduction:

  1. no electrical impulse
  2. impulse from SA node to AV node
  3. AV node to bundle of HIS to purkinje fibres
• Cardiac:

  1. diastole - blood enters the atria from the vena cava and the pulmonary vein. Atria + ventricles relax
  2. Atrial systole - both atria contract. Blood is forced from the atria to the ventricles
  3. Blood is forced from the ventricles to the aorta and pulmonary artery
• Cardiac output increases linearly with exercise intensity.
• Cardiac output plateaus as exercise intensity continues to rise towards maximal intensity
• Cardiac output increases at sub maximal exercise intensity because:

  1. HR and SV are increasing
  2. Q = HR x SV
• Cardiac output plateaus towards maximal exercise intensity because:

  1. HR continues to increase
  2. SV decreases because of cardiovascular drift
  3. so Q remains constant at its maximum value
• During recovery:

  1. Q reduces to its pre exercise value gradually
  2. HR decreases quickly but SV remains elevated
  3. a cool down helps to maintain Q
• Stroke volume increases linearly with exercise intensity
• Stroke volume plateaus as exercise intensity continues to rise
• At max intensity stroke volume decreases
• Max stroke volume is reached at sub maximal exercise intensity
• SV increases at submaximal exercise intensity because:

  • increased venous return and Starlings law of the heart
• Stroke volume plateaus at sub maximal exercise intensity and decreases at maximal exercise intensity because:

  1. HR increases as exercise intensity increases
  2. there is not enough time during ventricular diastole for ventricles to fill completely
  3. less blood in ventricles at end of diastole = decreased EDV
  4. less blood ejected from ventricles per beat
  5. decreased SV
  6. when SV decreases due to high HR it is called cardiovascular drift
• Starling‘s law of the heart:

  • SV depends on VR - the volume of blood returning
  • during exercise VR increases
  • causes walls of the heart to stretch: atrial + ventricular
  • which causes more stimulation of SA node (increased HR) and more forceful contractions of ventricular walls (increased SV)
• Stroke Volume during recovery:

  • remains elevated
  • reduces gradually
  • a comol down helps maintain SV
• SV at rest = 70ml
• SV at sub max = 120ml
• SV at max = 110ml
• SV for an athlete at rest = 100ml
• SV for an athlete at sub max = 160ml