partial pressure

• partial pressure of oxygen is a measure of oxygen concentration the greater the concentration of dissolved oxygen the greater the partial pressure
• the partial pressure of co2 is the measure of concentration of co2 in a cell
• haemoglobins affinity for oxygen varies depending on the partial pressure of oxygen. Oxygen loads onto haemoglobin to form oxyhaemoglobin where there's a high PO2.

  Oxyhaemoglobin unloads its oxygen where there's a lower pO2
• oxygen enters blood capillaries in the alveoli in the lungs. Alveoli have a high pO2 so oxygen loads onto haemoglobin to form oxyheamoglobin