We begin with a discussion of the origin of oxygen homeostasis, that is, conflicting selection pressures that drove the evolution of elaborate oxygen transport systems (Section 1), followed by a survey of the structure and function of the major gas-exchange systems found in invertebrates (Section 2) and vertebrates including mammals (Section 3) and birds (Section 4). This article traces the trajectory of respiratory complexity from invertebrates to vertebrates and as organisms moved from the deep ocean onto land and into the sky.
SKIN AND BONES THE KEEP THE KEEP ROCK 1995 SERIAL
Gas exchangers arose as simple air-blood diffusion interfaces that in active animals progressively gained in complexity in coordination with the cardiovascular system, leading to serial “step-downs” of oxygen tension to maintain homeostasis between uptake distribution and cellular protection.Īll gas exchangers share basic features, for example, thin blood-gas barrier, large interface, ventilatory regulation, and low cost of breathing. The respiratory organ is the “gatekeeper” that determines the amount of oxygen available for distribution. Each system is adapted to deliver enough oxygen and eliminate enough carbon dioxide to allow the species to surmount specific environmental and predatory pressures while simultaneously limiting the energy cost of breathing and cumulative oxidative stress in cells and organelles within an acceptable range. Harnessing the energy from oxidative phosphorylation while minimizing cellular stress and damage is an eternal struggle transcending specific organ systems or species, a conflict that shaped an assortment of gas-exchange systems. While aerobic respiration is essential for efficient metabolic energy production, a prerequisite for complex organisms, cumulative cellular oxygen stress has also made senescence and death inevitable. Oxygen, a vital gas and a lethal toxin, represents a trade-off with which all organisms have had a conflicted relationship. Through the evolutionary directions and variety of gas exchangers, their shared features and individual compromises may be appreciated. We, therefore, survey the comparative anatomy and physiology of respiratory systems from invertebrates to vertebrates, water to air breathers, and terrestrial to aerial inhabitants.
In an evolutionary context, certain species also become adapted to environmental conditions or habitual organismic demands. Within an organism's lifespan, the respiratory apparatus adapts in various ways to upregulate oxygen uptake in hypoxia and restrict uptake in hyperoxia. Here, we review the origin of oxygen homeostasis, a primal selection factor for all respiratory systems, which in turn function as gatekeepers of the cascade. Efficient respiratory gas exchange, coupled to downstream convective and diffusive resistances, comprise the “oxygen cascade”-step-down of PO 2 that balances supply against toxicity. Disparate systems exhibit similar directions of adaptation: toward larger diffusion interfaces, thinner barriers, finer dynamic regulation, and reduced cost of breathing. adult lungs) or simultaneous (e.g., skin, gills, and lungs in some salamanders). Habitat expansion compels the use of different gas exchangers, for example, skin, gills, tracheae, lungs, and their intermediate stages, that may coexist within the same species coexistence may be temporally disjunct (e.g., larval gills vs. Ambient oxygen tension ( PO 2) fluctuated through the ages in correlation with biodiversity and body size, enabling organisms to migrate from water to land and air and sometimes in the opposite direction.
to 4:30 p.m.Life originated in anoxia, but many organisms came to depend upon oxygen for survival, independently evolving diverse respiratory systems for acquiring oxygen from the environment. To find out if you have unclaimed property, search at or call the Treasury’s Unclaimed Property Division toll-free at 1-88 Monday through Friday, 10 a.m. One of the main reasons an item becomes unclaimed property is that a company has an incorrect or old address and it unable to return funds due. As a result, Treasury can clear out a backlog of unclaimed property still on the books and is able to mail checks to citizens without the need to file a claim. Act 339 of the 2018 Regular Session permits the Louisiana Department of Revenue to share its database of current addresses with the Treasury for the purpose of returning unclaimed property.
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