ABSTRACT
Oxygen (O2), the final electron acceptor in the respiratory chain of oxidative phosphorylation, is absolutely required for most living organisms, including all invertebrates and vertebrates. The delivery of atmospheric O2 via diffusion to individual cells within a tissue is limited if the organ dimension is more than 3 mm3 (Dachs and Tozer, 2000). Thus, in insects such as Drosophila, a tracheal (respiratory) system develops to meet the O2 demand for internal tissues. Although the O2 delivery system in mammals is far more complicated, consisting of respiratory, cardiac, vascular, and hematopoietic cells, the basic function is similar to that of the insect trachea, to transport O2. Since these systems were developed to supply O2, it is logical to state that the availability and concentration of O2 regulates development of these O2 delivery systems. Indeed, a great deal of data sustains this claim both in the Drosophila tracheal system and mammalian angiogenesis.
