Circulatory system

• Artery

  1. Arteries carry blood away from the heart
  2. Blood within the arteries is under the highest pressure
  3. They are elastic, this allows them to maintain the blood pressure 
  4. They have muscular walls that can adjust their diameter to increase or decrease blood flow to a particular part of the body
  5. Vasoconstriction - when the ring of muscle contracts which decreases the size of the diameter 
  6. Vasodilation - when the ring of muscle relaxes to increase the size of the diameter - occurs when exercising to allow more blood to flow to the exercising muscles(resulting in a reduction of blood pressure).
• Veins

  1. Veins carry blood back towards the heart
  2. They have much thinner walls than arteries because the blood pressure is much lower
  3. They have a large internal diameter - lumen
  4. They have valves to prevent the blood from flowing backwards
• Capillaries

  1. Capillaries are tiny, one cell thin walled blood vessels
  2. They join arteries and veins
  3. Due to their thin walls they are the site for gaseous exchange (oxygen passes from blood to tissues and carbon dioxide passes from tissues into the blood - we cover this in more detail when we look at the respiratory system)
• Heart diagram

  Consists of the vena cava, right atrium, tricuspid valve, right ventricle, semi-lunar valve, pulmonary artery, pulmonary vein, semi-lunar valve, left atrium, bicuspid valve, left ventricle and aorta.

  
• Pathway of blood

  1. Deoxygenated blood enters the right atrium

  2. Blood then travels into the right ventricle(through the tricuspid valve)

  3. The right ventricle contracts and forces the blood into the pulmonary artery (through the semilunar valve)

  4. The pulmonary artery takes the deoxygenated blood to the lungs

  5. Gaseous exchange occurs at the lungs - the blood gets oxygenated

  6. The pulmonary vein transports the newly oxygenated blood back to the heart

  7. The oxygenated blood enters through the left atrium

  8. Blood then flows into the left ventricle (Through Bicuspid valve)

  9. The blood is ejected from the left ventricle and travels along the aorta (semilunar valve)

  10. The aorta transports the blood to where it is needed in the body

  11. The vena cava takes the deoxygenated blood back to the heart

  12. Deoxygenated blood enters the right atrium
• Diastole

  • The atria and ventricles are relaxed and the valves between them are open.
  • Blood flows in from the blood vessels supplying the heart into the atrium before passing into the ventricle chamber
• Systole

  • The ventricles contract and pump blood out of the heart
  • The valves between the atria and ventricles snap shut preventing backflow…
  • Whilst the semi-lunar valves are forced open
• Valves

  Open due to pressure, and close to stop backflow of blood.
• Cardiac output

  The volume of blood that the heart pumps out per minute.

  Cardiac output = stroke volume x heart rate
• Stroke volume


  The volume of blood that leaves the heart during each contraction, e.g. on average 70ml
• Heart rate


  The number of times the heart beats each minute, e.g. on average 70bpm.
• Heart rate during exercise

  Heart rate increases, then it plateaued, before decreasing during recovery.

  
• Anticipatory rise

  The heart rate increases usually before activity because of the expectation of exercise. The body also releases adrenaline which increases the heart rate.
• Redistribution of blood

  Distribution of blood flow around the body is different at rest compared to exercise. Skeletal muscles require more oxygen, therefore more blood must be sent to them to satisfy the increased demand.The redirection of blood flow to where it is most needed is known as blood shunting or the vascular shunt mechanism.
• What happens when we exercise?

  Heart rate increases, stroke volume increases, cardiac output increases.
• Why does cardiac output increase when we exercise?

  When we exercise our muscles require more oxygen. To meet this increase in demand our heart beats faster and stronger.
• Volume of blood taken to different parts of the body at rest:

  Muscles - 15-20%

  Brain - 15%

  Heart - 4-5%

  Skeleton - 3-5%

  Digestive system - 20-25%

  Kidneys - 20%

  Skin - 4-5%
• Volume of blood taken to different parts of the body during exercise:

  Muscles - 80-85%

  Brain - 3-4%

  Skeleton - 0.5-1%

  Heart - 4-5%

  Digestive system - 3-5%

  Kidneys - 2-4%

  Skin - 1-2%
• Why is redistribution of blood important?

  • Increase the supply of oxygen to the working muscles
  • Remove waste products from the muscles, such as carbon dioxide and lactic acid
• How does redistribution of blood happen?

  • Vasoconstriction – blood vessels feeding the areas not needing so much blood become smaller, restricting blood flow to those tissues that are not needed during exercise 

  Vasodilation – blood vessels feeding the areas needing more blood (muscles, skin or heart) become wider, increasing blood flow / to move tissues that are needed during exercise.