3 Sections

• Venous return


  The pressure of the blood in large veins is very low which makes it difficult to get blood back to the heart
• Mechanisms needed to maintain venous return

  • Skeletal muscle pump
  • Respiratory pump
  • Pocket valves
  • Smooth muscle in veins
  • Heart
• Skeletal muscle pump


  When muscles contract and relax, they press on veins squeezing blood back to the heart
• Respiratory pump


  When muscles contract and relax during breathing, pressure changes occur in the chest cavity which compress nearby veins squeezing blood back to the heart
• Pocket valves


  Valves in veins keep the blood flowing in one direction and close to prevent backflow
• Smooth muscle in veins

  Squeeze the blood back to the heart
• Heart


  Acts as a suction pump when it contracts and relaxes
• When the systolic blood pressure increases

  There is an increase in venous return and vice versa
• Blood pressure


  The force exerted against the vessel wall
• Systolic pressure


  The pressure in the arteries when the ventricles contract
• Diastolic pressure


  The pressure in the arteries when the ventricles relax
• Blood pressure measurement


  At the brachial artery in the upper arm
• Typical blood pressure at rest

  120/80 mmHg
• Types of circulation


  • Pulmonary
  • Systemic
• Pulmonary circulation


  Deoxygenated blood from the heart to the lungs and oxygenated blood back to the heart
• Systemic circulation


  Oxygenated blood to the body from the heart and then the return of the deoxygenated blood from the body to the heart
• Blood vessels in order

  • Heart
  • Arteries
  • Arterioles
  • Capillaries
  • Venules
  • Veins
  • Heart
• Arteries


  • Thick elastic walls with a smooth muscle layer
  • Small lumen
  • Carry blood under high pressure and high velocity
  • Away from the heart
• Veins


  • Thinner less elastic walls with less smooth muscle than arteries
  • Large lumen
  • Carry blood under low pressure and medium velocity
  • Back to the heart
  • Contain non return valves
• Capillaries


  • One cell thick, no outer or middle layer
  • Microscopic lumen
  • Carry blood under very low pressure and very low velocity
  • Deliver oxygen and glucose to tissues and remove waste products from tissues
• After ten minutes in a warm environment


  The performer begins to sweat
• Sweating


  Causes a loss of fluid from the blood which decreases the plasma volume
• Decrease in the plasma volume

  Decreases the venous return and the stroke volume
• Decrease in stroke volume

  Heart rate keeps increasing to compensate
• Cardiac output


  Keeps increasing slowly to cool the body
• Cardiovascular drift


  Sweat, decreases plasma volume, decreases stroke volume and venous return, heart rate increases
• The leading cause of deaths in the UK is coronary heart disease
• Coronary heart disease


  When the coronary arteries supplying the heart with oxygenated blood become blocked due to a build-up of fatty deposits
• Atherosclerosis


  When the coronary arteries become blocked due to a build-up of fatty deposits
• Causes of atherosclerosis


  • High blood pressure
  • High cholesterol
  • Lack of exercise
  • Smoking
• Angina


  Chest pain caused by the coronary arteries narrowing meaning that they are unable to deliver enough oxygen to the heart
• Heart attack


  If a piece of atheroma breaks off in the coronary artery this can cause a blood clot cutting off the blood supply, resulting in a heart attack
• Regular exercise


  Keeps blood pressure and cholesterol low by making the heart bigger and stronger and maintaining flexibility of blood vessels ensuring good blood flow
• American Heart Association exercise recommendation

  At least 150 minutes per week of moderate exercise
• Regular aerobic exercise


  Lowers both systolic and diastolic pressure reducing the risk of a heart attack by up to 20%
• High blood pressure


  Puts extra strain on the arteries and heart and increases the risk of heart attack, heart failure and strokes
• Ischaemic stroke


  When a blood clot stops the blood supply to part of the brain
• Haemorrhagic stroke


  When a weakened blood vessel supplying the brain bursts
• Regular exercise


  Can help to lower blood pressure which can reduce the risk of a stroke by 27%
• Cardiac output


  The volume of blood pumped out by the heart per minute