FILL IN EVALUATION FORM

OXYGEN TRANSPORT

• Oxygen has a limited solubility in blood, in fact only about 1.5 % of oxygen carried in the blood is dissolved in the blood plasma

• The majority of oxygen is transported in blood by haemoglobin

• The reaction of oxygen with haemoglobin is temporary and completely reversible

Haemoglobin	+	Oxygen				Oxyhaemoglobin
Hb	+	O2				HbO2

• Each haemoglobin molecule contains 4 iron molecules that can each bind an O₂ molecule. Therefore each haemoglobin molecule is capable of carrying 4 O₂ molecules.

Hb	+	4O2				HbO8

• Haemoglobin loads/unloads one O₂ molecule at a time so Hb can exist as Hb (deoxyhaemoglobin), HbO₂, HbO₄, HbO₆ or HbO₈ (fully saturated oxyhaemoglobin).

• The binding of oxygen to haemoglobin is dependent on the partial pressure of oxygen (the partial pressure of a gas is the pressure one particular gas exerts in a mixture of gases).

Undergraduates click here for more information on partial pressures

• Oxygen combines with haemoglobin in oxygen-rich situations, such as the pulmonary capillaries. Oxygen diffuses rapidly from the alveoli to the capillaries due to the initial large difference in partial pressures (high in the alveoli, low in the capillaries).

• Equilibrium is never reached as oxygen is constantly being absorbed into the capillaries but new oxygen is continuously being brought to the alveoli.

• Oxygen is released by haemoglobin in oxygen-deficient situations, such as exercising muscle. When oxygen loaded blood reaches exercising tissues there is another large difference in partial pressures (high in blood, low in tissues), so oxygen diffuses into the tissues.

The relationship between the partial pressure of oxygen and the percentage of haemoglobin that has combined with oxygen to form oxyhaemoglobin (% haemoglobin saturation) is shown by the oxygen dissociation curve