biology paper 1

• Circulatory system


  A system of blood vessels with a pump and valves to ensure one-way flow of blood

  
• Types of circulatory systems in animals

  • Fish have a two chambered heart and a single circulation
  • Mammals have a four chambered heart and a double circulation

  
• Single circulatory system in fish


  Blood passes through the heart once for every one circuit of the body

  
• Double circulatory system in mammals

  1. Blood passes through the heart twice for every one circuit of the body

  2. Right side of heart receives deoxygenated blood from body and pumps it to lungs (pulmonary circulation)

  3. Left side of heart receives oxygenated blood from lungs and pumps it to body (systemic circulation)

  
• Advantages of double circulation

  • Blood travelling through small capillaries in lungs loses a lot of pressure, so returning blood to heart allows pressure to be raised again before sending to body
  • Allows cells to be supplied with oxygen and glucose for respiration faster and more frequently
• Heart


  • Labelled as if in chest, so left on diagram is right side and vice versa
  • Right side receives deoxygenated blood from body and pumps to lungs
  • Left side receives oxygenated blood from lungs and pumps to body
  • Blood pumped towards heart in veins, away from heart in arteries
  • Two sides separated by muscle wall called septum
  • Made of muscle tissue supplied by coronary arteries

  
• Heart structure


  • Ventricles have thicker muscle walls than atria as they pump blood out of heart and need to generate higher pressure
  • Left ventricle has thicker wall than right as it pumps blood at high pressure around body, right ventricle pumps to lungs at lower pressure
  • Septum prevents mixing of oxygenated and deoxygenated blood

  
• Pathway of blood through heart

  1. Deoxygenated blood flows into right atrium via vena cava

  2. Blood pushed through tricuspid valve into right ventricle

  3. Ventricle contracts, blood pushed into pulmonary artery through semilunar valve

  4. Blood travels to lungs for gas exchange

  5. Oxygenated blood returns to left atrium via pulmonary vein

  6. Passes through bicuspid valve into left ventricle

  7. Ventricle contracts strongly to push blood into aorta around body

  8. Semilunar valve in aorta prevents backflow

  
• Valves


  • Prevent blood flowing backwards
  • Atrioventricular valves (tricuspid and bicuspid) separate atria from ventricles
  • Semilunar valves in arteries leaving heart

  
• Heart activity can be monitored by ECG, pulse rate, or listening to valve sounds

  
• During exercise


  Heart rate increases
• Why heart rate increases during exercise

  • To supply working muscles with more oxygen and nutrients, and remove waste products faster
  • To 'repay' oxygen debt built up from anaerobic respiration during exercise
• Coronary arteries


  Supply heart muscle with blood, oxygen and nutrients

  
• Partial blockage of coronary arteries

  Causes restricted blood flow and angina

  
• Complete blockage of coronary arteries

  Causes heart attack as heart muscle cells can no longer respire

  
• Risk factors for coronary heart disease

  • Poor diet
  • Stress
  • Smoking
  • Genetic predisposition
  • Age
  • Gender

  
• Angioplasty


  Balloon inserted into blocked artery to flatten plaque, then stent inserted to keep artery open

  
• Coronary bypass surgery


  New blood vessel taken from patient's body used to bypass blocked area of coronary artery

  
• Arteries


  Carry blood at high pressure away from heart, have thick muscular walls, narrow lumen, fast flow

  
• Veins


  Carry blood at low pressure towards heart, have thin walls, large lumen, contain valves, slow flow

  
• Coronary bypass graft


  Procedure that improves the flow of blood to the cardiac muscle, bypassing the blocked area

  
• Number of bypass grafts


  Gives rise to the name of the surgery, so a 'triple heart bypass' would mean three new bypass grafts being attached

  
• Arteries


  • Carry blood at high pressure away from the heart
  • Carry oxygenated blood (other than the pulmonary artery)
  • Have thick muscular walls containing elastic fibres
  • Have a narrow lumen
  • Speed of flow is fast

  
• Veins


  • Carry blood at low pressure towards the heart
  • Carry deoxygenated blood (other than the pulmonary vein)
  • Have thin walls
  • Have a large lumen
  • Contain valves
  • Speed of flow is slow

  
• Capillaries


  • Carry blood at low pressure within tissues
  • Carry both oxygenated and deoxygenated blood
  • Have walls that are one cell thick
  • Have 'leaky' walls
  • Speed of flow is slow

  
• Arterioles


  The narrow vessels that connect arteries to capillaries

  
• Venules


  The narrow vessels that connect capillaries to veins

  
• Shunt vessels


  Vessels that can open or close to control the amount of blood flowing to a specific area

  
• When we are hot

  More blood flows through the surface of the skin
• When we are cold

  Less blood flows through the surface of the skin
• Lymph fluid


  Excess fluid that leaks out of the capillaries and passes into the lymphatic system
• Lymph vessels and nodes

  • The lymphatic system is formed from a series of tubes which flow from tissues back to the heart
  • Lymph nodes are small clusters of lymphatic tissue found throughout the lymphatic system, especially in the neck and armpits
  • Large numbers of lymphocytes are found in lymph nodes
  • Tissues associated with the lymphatic system, such as bone marrow, produce these lymphocytes
  • Lymphocytes play an important role in defending the body against infection

  
• Red blood cells


  • Biconcave discs containing no nucleus but plenty of the protein haemoglobin
• White blood cells


  • Large cells containing a big nucleus, different types have slightly different structures and functions
• Platelets


  • Fragments of cells
• Plasma


  • Straw coloured liquid
• Phagocytes


  Carry out phagocytosis by engulfing and digesting pathogens
• Lymphocytes


  Produce antibodies to destroy pathogenic cells and antitoxins to neutralise toxins released by pathogens
• Blood clotting


  Platelets release chemicals that cause soluble fibrinogen proteins to convert into insoluble fibrin and form an insoluble mesh across the wound, trapping red blood cells and therefore forming a clot
• Plasma is important for the transport of carbon dioxide, digested food (nutrients), urea, mineral ions, hormones and heat energy