Cardiovascular L3

• Deirdre Merry is from the School of Biological Sciences at the University of Canterbury
• Blood components


  • Plasma
  • Buffy coat (leukocytes and platelets)
  • Erythrocytes (red blood cells)

  
• Haematocrit


  Percentage of red blood cells in a sample of whole blood

  
• Blood plasma


  • About 90% water
  • Contains dissolved ions, plasma proteins, lipid transport, immunity, blood clotting

  
• Mammalian red blood cells

  • Do not have a nucleus
  • Bi-concave shape to increase surface area

  
• Leukocytes


  • Important for immunity and defense
• Platelets


  • Responsible for blood clotting
• The cellular elements of blood are constantly replaced throughout a person's life; erythrocytes have a lifespan of 3 – 4 months
• HIF


  Hypoxia inducible factor

  
• Red blood cells


  • Primary function is to transport oxygen from the lungs (or gills) to tissues
  • Each RBC is packed with haemoglobin molecules (respiratory pigment)
  • Most O2 in animal circulatory systems is bound to haemoglobin or haemocyanin

  
• Haemoglobin molecule


  • Each molecule contains 4 globin subunits
  • Each globin subunit contains a haeme group surrounding a ferric ion (Fe2+)
  • Each globin subunit can reversibly bind to one molecule of O2
• Vertebrate haemoglobin is contained within red blood cells

  
• O2 capacitance


  Determined by the concentration of respiratory pigment (e.g. haemoglobin) in blood

  
• Concentration of respiratory pigment increases with metabolic rate and in breath-holding diving vertebrates
• Haemoglobin conformational states


  Tense and Relaxed
• Cooperative binding


  The probability of haemoglobin being in the relaxed state is increased with the binding of O2 to any of the four binding sites
• Haemoglobin-oxygen bonds display "co-operative binding"

  
• Haemoglobin "affinity" reflects the strength of the Hb-O2 bond which depends on amino acid sequence of globin subunits (Hb isoforms) and chemical microenvironment surrounding Hb

  
• P50


  The PO2 at which Hb is 50% saturated with O2, a measure of oxygen affinity
• High P50


  Low affinity
• Low P50


  High affinity
• Shift to the left = lower P50, high affinity. Shift to the right = higher P50, low affinity
• Factors modifying Hb-O2 binding affinity

  • Increase in temperature increases the probability that Hb will be in a tense state
  • Decrease in pH decreases affinity (right shift)
  • H+ ions bind to sites on globin subunits and this increases the probability of Hb being in a tense state
• Blood pH, PCO2, and temperature (to a lesser extent) differ in gas exchange organs and tissues

  
• Gas exchange organ


  Increased pH, decreased PCO2, decreased temperature - Left shift, increases Hb-O2 affinity, facilitates loading of O2 onto Hb
• Tissues


  Decreased pH, increased PCO2, increased temperature - Right shift, decreases Hb-O2 affinity, facilitates offloading of O2 from Hb
• Bohr effect


  A lower pH causes Hb to release more oxygen, a higher pH causes Hb to hold more oxygen
• Blood doping in sports

  Illicit method of enhancing athletic performance by artificially increasing haemoglobin concentrations through blood transfusions, EPO injection, or synthetic oxygen carriers
• Blood boosting in the animal kingdom - Animals can naturally boost the number of RBCs in their circulation through splenic contraction in response to metabolically demanding activities and apnoea
• Blood viscosity increases as temperatures decrease, by about 2% for every 1°C drop in temperature. Antifreeze proteins also increase viscosity, which is a problem for fish inhabiting sub-zero environments
• The bald notothen (Pagothenia borchgrevinki) can increase its blood oxygen carrying capacity by up to 207% through splenic contraction, which minimises the energetic costs associated with transporting highly viscous blood and enables an active lifestyle in an extreme environment