Zoology · Ch 6 — Respiration
Transport of Oxygen
Transport of Oxygen
Only about 3% of the oxygen carried in blood travels dissolved directly in the plasma, because oxygen is not very soluble in water. The remaining 97% binds reversibly to haemoglobin inside red blood cells to form oxyhaemoglobin (HbO2); since each haemoglobin molecule carries four iron atoms, it can bind up to four oxygen molecules at once.
How readily haemoglobin binds or releases oxygen is governed by the local partial pressure of oxygen, and also by pCO2, temperature and H+ concentration. In the alveoli - high pO2, low pCO2, low temperature, low H+ - these conditions all favour haemoglobin binding oxygen tightly, forming oxyhaemoglobin. In actively respiring tissues - low pO2, high pCO2, high temperature, high H+ - the same conditions reverse, favouring the dissociation (release) of oxygen from oxyhaemoglobin exactly where it is needed. …
What this figure shows. An S-shaped (sigmoid) curve plotting the percentage saturation of haemoglobin with oxygen (y-axis) against the partial pressure of oxygen in mm Hg (x-axis) - steep in the low-pO2 range between about 10 and 50 mm Hg, and flattening out between about 70 and 100 mm …