Physiology, Oxyhemoglobin Dissociation Curve

Oxygen is primarily transported throughout the body in red blood cells, attached to hemoglobin molecules. Oxygen is also dissolved directly in the bloodstream, but this dissolved fraction contributes little to the total amount of oxygen carried in the bloodstream. Henry’s Law states that the dissolved fraction is proportional to the atmospheric pO2, but the solubility of oxygen is so low that only 3ml O2/L of blood is dissolved at atmospheric oxygen tension. Hemoglobin carries 98% of the oxygen in the blood in the protein-bound form, approximately 197 ml/L. It is important to differentiate between pO2 (mm Hg, the dissolved fraction), oxygen saturation (% of hemoglobin occupied), and O2 content (expressed as a volume percentage). Arterial oxygen content is approximately 20 g/dL, the venous oxygen content is 15 g/dL, and dissolved oxygen contributes 0.1 g/dL in each case (but is continuously replenished from the hemoglobin bound pool).