The cardiac output is distributed throughout the body via the arterial circulation. Thus, there is an oxygen reserve which can be called upon should demand for O2 increase. However, during active, sustained exercise, the skeletal muscle oxygen consumption can increase by a factor of twenty. In this case, the increased demand is met by an increase in the blood flow. In later lectures, you will learn how organ blood flow is adjusted to respond to an increase in nutrient demand.
Oxygen leaves the blood at the level of the microcirculation.
As mentioned, oxygen is a small, lipid soluble, highly diffusable molecule. Overview of oxygen transport from the atmosphere to the red blood cells and unloading of oxygen from the red cell in the microvascular exchange vessels. Comparison of Oxygen Supply and Demands of Skeletal and Cardiac Muscle. In addition, to increased blood flow, the heart must extract more oxygen from each ml of blood to meet it's oxygen needs. To increase oxygen extraction, the heart has a rich capillary network that enhances oxygen transport from blood to tissue.