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How multicellular organisms obtain and use oxygen and other substrates has evolved over hundreds of millions of years in parallel with the evolution of oxygen-delivery systems. A steady supply of oxygen is critical to the existence of organisms that depend on oxygen as a primary source of fuel (i.e., those that live by aerobic metabolism). Not surprisingly, a number of mechanisms have evolved to defend against oxygen deprivation. This review highlights evolutionary and developmental aspects of O2delivery to allow understanding of adaptive responses to O2deprivation (hypoxia). First, we consider how the drive for more efficient oxygen delivery from the heart to the periphery may have shaped the evolution of the cardiovascular system, with particular attention to the routing of oxygenated and deoxygenated blood in the cardiac outlet. Then we consider the role of O2in the morphogenesis of the cardiovascular system of animals of increasing size and complexity. We conclude by suggesting areas for future research regarding the role of oxygen deprivation and oxidative stress in the normal development of the heart and vasculature or in the pathogenesis of congenital heart defects. [ABSTRACT FROM AUTHOR]

There is currently tremendous interest in how the physiology of individual animals changes and develops during ontogeny. One of the key areas is the extent to which the timing and/or rate of physiological development is fixed within an individual and to what extent can it be altered. We propose that plasticity in the timing of the onset of a particular physiological regulatory system during an individuals development be referred to as physiological heterokairy (to clearly distinguish this phenomenon from physiological heterochrony, which is an evolutionary pattern), and we marshal evidence for three different patterns of heterokairy: 1. altering relative position in the physiological itinerary; 2. altering overall rate of development per se and; 3. a combination of 1 and 2. Using these patterns as a starting point, we develop a framework for investigating physiological heterokairy which takes cognizance of the facts that multiple components of each regulatory system could appear at different times and multiple regulatory systems could come 'on-line' at different times. We finish by placing physiological heterokairy in the wider context of its ecological and evolutionary implications and its relationship to physiological genomics and heterochrony. [ABSTRACT FROM AUTHOR]