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• The gasses in the alveoli with the blood come into equilibrium

  Due to diffusion across the pulmonary epithelium and the capillary wall
• Diffusion

  Due to the difference in partial pressure of the gasses between the alveoli and the blood
• Partial pressure

  The pressure exerted by an individual gas of a mixture
• Dalton's law of partial pressure states that the total pressure of the mixture of gasses is the sum of the individual gasses
• Each gas exerts a partial pressure, independent of each other
• Fick’s law of diffusion

  The difference in partial pressure on the surface area of the membrane and two sides of the membrane of an alveolus determines the amount of oxygen or carbon dioxide that is diffused across the membrane
• The partial pressure in the arterial blood is 100mmHg and in the tissues is 40mmHg
• Due to the partial pressure of oxygen being lower in cells

  The oxygen diffuses its pressure into the cells
• Oxygen has poor solubility in blood (0.25ml/100ml)
• Average person has around 5L blood where 12.5 ml is dissolved oxygen, which is insufficient for respiration
• Blood actually contains 20mL/100ml oxygen
• Hemoglobin can combine reversibly with RBC and greatly increase the capacity of the RBC to deliver oxygen throughout the body
• Blood contains a large concentration of hemoglobin (140-180g/L for men and 120-160g/L for women)
• Hemoglobin contains 2 alpha and 2 beta peptide chains
• Each polypeptide contains a haem group that can reversibly bind to oxygen and each haem group contains an iron atom at the center
• A hemoglobin molecule can bind up to four oxygen molecules
• Oxygen binding is cooperative, the binding of one site increases the ability of the others site to be binded to
• Oxygen-hemoglobin dissociation curve is the relationship between the partial pressure of oxygen and the percentage saturation of hemoglobin in the blood
• As the oxygen concentration increases, there is an increase in the hemoglobin binding which is the highest at pulmonary capillaries
• Due to cooperative binding of oxygen to hemoglobin, the relationship is not linear but sigmoid
• There are different factors that affect the binding of hemoglobin and the release of oxygen such as pH, CO2 concentration, 2,3-BPG, and temperature
• Right shift in the curve states that there is a decrease in the affinity of oxygen to hemoglobin
• Left shift of the curve states that the carbon dioxide concentration, pH, 2,3-BPG, and temperature have all decreased
• Bohr effect states that due to a change in pH, there is a displacement in the oxygen hemoglobin dissociation curve
• Carbon dioxide in the tissue reacts with the water in the plasma to form carbonic acid
• Increase in carbon dioxide will increase the acidity, therefore reduce the pH of the blood
• Oxyhaemoglobin unloads oxygen more readily in an acidic pH than in a normal pH
• More than oxyhaemoglobin, deoxyhemoglobin binds readily to H+ ions
• At low affinity states, oxygen is easily released due to the stability of the hemoglobin chain due to the binding of H+ ions to the specific amino acids on the globin chain
• When lactic acid is released in the muscle, it lowers the blood pH which has a similar effect on the oxygen hemoglobin dissociation
• Deoxyhemoglobin

  Binds readily to H+ ions
• Low affinity states

  Oxygen is easily released due to the stability of the hemoglobin chain from the binding of H+ ions to specific amino acids on the globin chain
• Lactic acid is released in the muscle

  It lowers the blood pH which has a similar effect on the oxygen hemoglobin dissociation curve
• Utilization coefficient

  The fraction of blood that gives up its oxygen when it passes through the capillary bed
• Under normal conditions, 5ml/100ml of blood will be released to the tissues, therefore 25% of the oxygen present in the blood is utilized by the tissue
• Venous blood still contains 15 ml of oxygen /100ml of blood
• During strenuous exercise, the rate of oxygen delivery is increased three times its normal delivery
• This can lead to cardiac output being increased by 5 times, therefore the total increase in oxygen delivery is 15 times
• Ways carbon dioxide can be transported

  • Dissolved in solution
  • Transported as carbonic acid
  • Bound to proteins such as hemoglobin
• CO2 in solution is 2.5ml/100 ml, however, blood can carry 50ml/100ml of carbon dioxide indicating only 5% is in solution