I think it may be conservation.
Autosomes. The somatic chromosomes are referred to as autosomes.
Oxygen-poor blood goes into the lungs and through the lung capillaries after leaving the heart. It does so to be oxygenated by the lungs. The oxygen in the lungs comes from the air we breath. Once the blood is oxygenated, it goes back into the heart, to be pumped back into our bodies for distribution.
