Cardiovascular system

• Cardiac response to exercise and recovery

  1. SA node releases electrical impulse across atrial chambers

  2. Atrial systole (contraction of atria, forcing blood through bicuspid + tricuspid valves into ventricles)

  3. Cardiac impulse reaches and activates AV node, which delays impulse to allow atria to finish contracting

  4. Bundle of His splits impulse down left + right bundle branches into Purkinje fibers, which transmit impulse through walls of ventricles causing them to contract; force blood out through semi-lunar valves
• Heart rate responses


  • Sub-maximal exercise: Initial anticipatory rise in HR, rapid increase in HR to increase blood flow at start of exercise, steady state HR throughout
  • Maximal exercise: Rapid increase in HR, sustained intensity exercise, initial rapid decrease in HR as recovery is entered and muscle pump action decreases
• Stroke volume response


  Stroke volume depends on venous return, increases in proportion to exercise intensity until a plateau is reached at 40-60% of working capacity
• Cardiac output response


  Cardiac output is the product of heart rate and stroke volume, increases in line with exercise intensity and plateaus during maximal exercise
• UR (venous return) mechanisms

  • Increased venous return, greater volume of blood returning to heart and filling ventricles, due to squeezing action of muscular contraction around veins (muscle pump)
  • Increased temperature
  • Gravity
  • Vascular shunt mechanism (redistribution of blood from non-essential organs to working muscles)
• Neural control


  • Baroreceptors detect increased stretch on arterial walls due to increased blood pressure, send information to cardiac control centre in medulla oblongata
  • Chemoreceptors detect changes in O2/lactic acid, send information to cardiac control centre
  • Proprioceptors detect increased motor/muscle activity, send information to cardiac control centre
• Sympathetic nervous system


  Responsible for increasing heart rate, specifically during exercise
• Parasympathetic nervous system


  Responsible for decreasing heart rate, during recovery
• Hormonal control


  Adrenaline and noradrenaline stimulate sympathetic nervous system, increasing speed of nerve transmission, firing rate of SA node, and force of ventricular contraction
• Intrinsic control


  Frank-Starling mechanism/Starling's law - stroke volume is dependent on venous return
• Vasomotor control (UCC) - stimulation sent to arterioles and pre-capillary sphincters to redistribute blood flow from non-essential organs to working muscles during exercise
• Cardiac cycle

  Blood moves through the heart
• At the end of the previous cardiac cycle, both the atria and ventricles are in diastole (relaxed)
• Blood flow during diastole

  1. Blood flows into the atria through the vena cava and pulmonary vein

  2. Pressure in the atria rises

  3. Atrioventricular valves open

  4. Blood flows down from the atria into the ventricles
• Atrial systole


  1. Atria contract

  2. Remaining blood pushed from the atria down to the ventricles
• Ventricular systole

  1. Ventricles contract

  2. Ventricular pressure rises rapidly

  3. Atrioventricular valves close

  4. Semilunar valves in the pulmonary artery and aorta open

  5. Blood pumped from the ventricles out of the heart
• When the ventricles contracted, the atria relaxed
• Ventricular diastole

  1. Ventricles relax

  2. Ventricular pressure falls below the pressure in the pulmonary artery and aorta

  3. Semilunar valves shut

  4. Heart ready to enter the next cardiac cycle