Question

Amount of oxygen supplied by 100 ml arterial blood, while passing through the tissues is

• A. 0.4 - 0.6 ml
• B. 4 - 6 ml
• C. 14 - 15 ml
• D. 19 - 20 ml

Answer 1

Answer: (B)

4 - 6 ml

The total quantity of oxygen carried by 100 ml of blood is sum total of oxygen contained in RBC and oxygen dissolved in blood plasma. Since 1 gm of fully oxygenated Hb contains 1.39 ml of oxygen at 100 mm of Hg pressure and average haemoglobin level of adult human is 15 gm/100ml blood. Therefore, total oxygen content of 100mL of arterial blood at 100 mm Hg pressure is 1.39 x Hb x % of saturation +0.003 x partial pressure of oxygen = 1.39 x 15 x 1 +0.003 x 100=21.15 ml/100 ml.

Since the partial pressure of oxygen in venous blood is 40 mm Hg and haemoglobin is 75% saturated. So, the oxygen content of 100 ml of venous blood at 100 mm Hg pressure = 1.39 x 15 x 0.75 +0.003 x 40 = 15.75 ml/100 ml. This means that at tissue level, 21.15-15.75 = 5.4 ml of oxygen is being extracted, which makes option B correct answer.