Physiology of marathons amounts of blood to and from the lungs to reach all bodily tissues is dependent on having a high cardiac output along with sufficient levels of total body hemoglobin. Hemoglobin is the oxygen carrying protein within blood cells that allows for the proper transportation of oxygen from the lungs to other bodily tissues via the circulatory system. In order for the transportation of oxygen in blood to be effective during a marathon, the distribution of blood needs to be equally efficient in order for a marathoner's oxygen demands to be met during a race. The mechanism that allows for this
Vascular remodelling in the embryo early cardiovascular flow, such as preventing the entry of red blood cells into blood plasma, thereby lowering viscosity and associated shear stresses. Starch can also be injected into the blood stream in order to increase viscosity and shear stress. Studies have shown that vascular remodelling in the embryo proceeds without the presence of erythrocytes, which are responsible for oxygen delivery. Therefore, vascular remodelling does not depend on the presence of oxygen and in fact occurs before perfused tissues require oxygen delivery. However, it is still unknown whether or not other nutrients or genetic factors may have promotional effects on vascular