O2 saturation in venous blood-

Ans. is 'c' i.e., 75% * In vivo, the hemoglobin in the blood at the ends of the pulmonary capillaries is about 97.5% saturated with O2.* Because of a slight admixture with venous blood that bypasses the pulmonary capillaries (physiological shunt), the hemoglobin in systemic arterial blood is only 97% saturated.* The arterial blood therefore contains a total of about 19.8 ml of O2 per dl; 0.29 ml in solution and 19.5 ml bound to hemoglobin (as oxyhemoglobin).* In venous blood at rest, the hemoglobin is 75% saturated and the total O2 content is about is 15.2 mg/dl; 0.12 ml in solution and 15.1 ml bound to hemoglobin.* Thus, at rest tissues remove about 4.6 ml of O2 from each deciliter of blood passing through them.* 0.17 ml of this total represents O2 that was in solution in the blood, and the remainder represents O2 that was liberated from hemoglobin.* In this way, 230 ml (by 5 litre of blood) of O2 per minute is transported from the blood to the tissues at rest.