venous return

• • during exercise, VR increases
  • more blood being pumped back to the heart means more blood should be pumped out so SV increases - starling's law
• starling's law is concerned with

  1. elasticity of cardiac muscle
  2. degree of stretch of cardiac tissues during diastole phase of cardiac cycle
• what is the impact of ejection fraction due to increased VR

  increased VR = greater diastolic filling of the heart leading to cardiac muscle being stretched so more force of contraction increasing ejection fraction - starling's law
• why does ejection fraction increase

  because of SV as more stretch of cardiac tissues so ejects more blood
• venous return mechanisms

  • skeletal muscle pump
  • respiratory pump
  • pocket valves
  • smooth muscles
  • suction pump
  • gravity
• skeletal muscle pump

  • when muscles contract and relax, they change shape
  • change in shape means muscles press on veins causing a pumping effect and squeezes blood to the heart
• respiratory pump

  • when muscles contract and relax during breathing in and out, pressure changes occur in chest (thoracic) and abdominal cavities (stomach)
  • changes in pressure compress the veins and assist in blood return to heart
• pocket valves

  • important that blood flows in one direction
  • valves ensure this as once blood has passed through the valves, they close to prevent backflow of blood
• smooth muscle

  thin layer of smooth muscles in walls of veins helps squeeze blood back to heart
• suction pump

  suction pump action of heart - more blood pumped out of the heart, so more blood then drawn
• gravity

  helps blood return to heart from upper body
• what happens to mechanisms after exercise


  maintained - done by performing cool downs to prevent blood pooling
• why is it important to maintain VR

  • ensures skeletal muscles receives enough O2 to meet demands of activity
  • at rest smooth muscles and veins are sufficient enough to maintain VR but not during exercise
  • as demand for O2 increases and heart beats faster so vascular system helps out
• 70% of blood volume is contained at rest - means a large amount of blood can be returned to the heart if needed