The Heart and Blood

• Fish have a single circulatory system where deoxygenated blood is pumped from the heart to the gills, becomes oxygenated, and then passes straight to the organs
• The problem with a single circulatory system is that the blood loses a lot of pressure as it passes through the gills before reaching the organs, so the blood travels to the organs relatively slowly and cannot deliver a great deal of oxygen
• Humans have a double circulatory system where deoxygenated blood is pumped from the heart to the lungs, becomes oxygenated, and then returns to the heart to be pumped to the organs
• The benefit of the double circulatory system is that the blood passes through the heart twice, allowing it to travel rapidly to the body cells and deliver the oxygen they need
• Heart


  • Organ consisting mainly of muscle tissue
  • Job is to pump blood around the body
• Chambers of the heart

  • Left atrium
  • Right atrium
  • Left ventricle
  • Right ventricle
• The atria are separated from the ventricles by valves
• Blood vessels entering and leaving the heart

  • Vena cava (brings in oxygenated blood from the body)
  • Pulmonary artery (blood passes from heart to lungs)
  • Pulmonary vein (oxygenated blood passes from lungs to heart)
  • Aorta (blood is pumped from heart to body)
• Pattern of blood flow through the heart

  1. Blood enters left and right atria

  2. Atria contract, forcing blood into ventricles

  3. Ventricles contract, forcing blood out of heart

  4. Valves prevent backflow into atria
• Left ventricle


  • Has thicker muscular wall than right ventricle
  • Pumps blood around entire body, so needs greater force
• Right ventricle


  • Only pumps blood to the lungs
• Coronary arteries


  • Branch out of the aorta and spread into the heart muscle
  • Purpose is to supply oxygen to the muscle cells of the heart
• Pacemaker


  Group of cells found in the right atrium that control the natural resting heart rate
• If the pacemaker stops working correctly, doctors can implant an artificial pacemaker to correct irregularities in the heart rate
• Arteries


  Carry very high pressure blood from the heart to the organs in the body
• Arteries


  • Have very thick muscular walls to withstand the very high pressure of the blood
  • Contain elastic fibers that stretch when the surge of blood passes through and then recoil in between the surges to keep the blood moving
• Capillaries


  Where substances such as glucose and oxygen diffuse from the blood to the cells, and carbon dioxide diffuses from the cells back to the blood
• Capillaries


  • Have very thin walls so the diffusion pathway is very short, allowing substances to diffuse rapidly between the blood and the body cells
• Veins


  Carry blood back to the heart
• Veins


  • Have thin walls because the blood pressure is low
  • Contain valves that stop blood flow backwards when the blood is flowing in the correct direction
• The structure of arteries, veins and capillaries relates to their function in the circulatory system
• Cardiovascular diseases


  Diseases of the heart and blood vessels
• Cardiovascular diseases


  • They are non-communicable, meaning they cannot be passed from person to person
• Coronary heart disease


  1. Layers of fatty material build up inside the coronary arteries

  2. Coronary arteries narrow

  3. Reduces blood flow and oxygen to the heart muscle

  4. Can result in a heart attack
• Statins


  Drugs which reduce the level of cholesterol in the blood, slowing down the buildup of fatty materials in the arteries
• Statins


  • Effective at reducing the risk of coronary heart disease
  • Can cause unwanted side effects like liver problems
• Stent insertion


  1. Stent is a tube inserted into the coronary artery to keep it open

  2. Allows normal blood flow but does not treat underlying causes
• Heart valve issues


  Valves do not fully open or are leaky, causing the heart to work harder
• Mechanical heart valves


  Made of metal, can last a lifetime but increase risk of blood clots
• Biological heart valves


  From animals, do not last as long and may need replacement, but do not require anti-clotting drugs
• Heart failure


  Heart cannot pump enough blood around the body
• Heart transplant


  1. Donated heart or heart and lungs transplanted

  2. Shortage of donated hearts

  3. Patient must take drugs to prevent rejection
• Artificial heart


  • Temporary solution to allow damaged heart to rest or while waiting for transplant
  • Increases risk of blood clots, not a long-term solution
• Blood plasma


  The liquid part of the blood
• Functions of blood plasma

  1. Transports dissolved substances around the body

  2. Transports soluble digestion products from small intestine to other organs

  3. Transports carbon dioxide from body cells to lungs

  4. Transports waste product urea from liver to kidneys
• Red blood cells


  • Contain the oxygen-carrying molecule hemoglobin
  • Have no nucleus, allowing more space for hemoglobin
  • Have a biconcave disk shape for greater surface area
• Function of red blood cells

  Transport oxygen from lungs to body cells
• White blood cells


  • Part of the immune system, make antibodies
  • Contain a nucleus with DNA
• Platelets


  Tiny fragments of cells that help the blood to clot
• Uses of donated blood

  • Replace blood loss during injury
  • Platelets extracted to help clotting
  • Proteins extracted, e.g. antibodies