Question

what percentage of bound oxygen does hemoglobin release between 100 and 30 torr of pO2? a. 97% b. 95% c. 55% d. 40% e. 6%

Answer 1

Ans. The oxygenated blood in arteries has pO₂ =95 torr (97.5% saturation; 19.6 mL Hb-bound O₂ per dL blood). The tissues have relatively very low pO₂ due to continuous O₂ consumption for cellular respiration. The capillaries emerging out from tissues after delivering O₂ to tissues have pO₂ 40 torr (75 % saturation; 15.2 mL Hb-bound O₂ per dL blood). Overall, there is delivery of around 4.6 mL O₂/ dL blood to the tissues during passage of oxygenated blood through it. This amount of O₂, actually being delivered to tissues by oxygenated blood, is called O₂-utilization coefficient of blood (4.6 mL O₂/ dL blood).

At 30 torr pO₂, % Hb saturation is around 60%.

So,

Amount of O₂ bound to Hb at 60% saturation = 60% of O₂ 97.5 % (=100%) saturation

                                                = 60 % of 19.6 mL

                                                = 11.76 mL

# Amount of O₂ bound to blood at 97.5 % Hb saturation (equivalent to 100% saturation at physiological condition) = 19.6 mL

# Now,

Amount of O₂ released from 100% to 60% Hb saturation = 19.6 mL – 11.76 mL

                                                            = 7.84 mL

% O₂ released = (Amount of O₂ released / O₂ in 100% saturated blood) x 100

                                    = (7.84 mL / 19.6 mL) x 100

                                    = 40.0 %

Thus, correct option is – D. 40.0 %