Blood

• Oxygen loading


  The process by which haemoglobin binds with oxygen is called loading or associating. In humans this takes place in the lungs.
• Oxygen unloading


  The process by which haemoglobin releases its oxygen is called unloading or dissociating. In humans this takes place in the tissues.
• High affinity


  Haemoglobins with this for oxygen take up oxygen more easily, but release it less easily.
• Low affinity


  Haemoglobins with this for oxygen take up oxygen less easily, but release it more easily.
• Oxygen dissociation curve is the graph of the relationship between the saturation of haemoglobin with oxygen and the partial pressure of oxygen.
• At low oxygen concentrations, not much oxygen binds to haemoglobin.
• After the first oxygen molecule binds to haemoglobin, the quaternary structure of the haemoglobin molecule changes, making it easier for the other subunits to bind an oxygen molecule, therefore it takes a smaller increase in the partial pressure of oxygen to bind the second molecule and third molecule, steepening the gradient of the curve.
• After the binding of the third molecule, it is less likely that a single oxygen molecule will find an empty site to bind to, reducing the gradient of the curve and causing the graph to flatten off.
• Bohr Shift

  The greater the concentration of carbon dioxide the more readily the haemoglobin releases its oxygen because the more carbon dioxide there is, the lower the pH, the greater the haemoglobin shape change, the more readily oxygen is unloaded, the more oxygen is available for respiration.