B3.1 Gas Exchange

Journal of Anatomy, 2002

Over the evolutionary continuum, animals have faced similar fundamental challenges of acquiring molecular oxygen for aerobic metabolism. Under limitations and constraints imposed by factors such as phylogeny, behaviour, body size and environment, they have responded differently in founding optimal respiratory structures. A quintessence of the aphorism that 'necessity is the mother of invention', gas exchangers have been inaugurated through stiff cost-benefit analyses that have evoked transaction of trade-offs and compromises. Cogent structuralfunctional correlations occur in constructions of gas exchangers: within and between taxa, morphological complexity and respiratory efficiency increase with metabolic capacities and oxygen needs. Highly active, small endotherms have relatively better-refined gas exchangers compared with large, inactive ectotherms. Respiratory structures have developed from the plain cell membrane of the primeval prokaryotic unicells to complex multifunctional ones of the modern Metazoa. Regarding the respiratory medium used to extract oxygen from, animal life has had only two choices -water or air -within the biological range of temperature and pressure the only naturally occurring respirable fluids. In rarer cases, certain animals have adapted to using both media. Gills (evaginated gas exchangers) are the primordial respiratory organs: they are the archetypal water breathing organs.

Open Access Animal Physiology, 2014

Acquisition of molecular oxygen (O 2 ) from the external fluid media (water and air) and the discharge of carbon dioxide (CO 2 ) into the same milieu is the primary role of respiration. The functional designs of gas exchangers have been considerably determined by the laws of physics which govern the properties and the flux of gases and the physicochemical properties of the respiratory fluid media (water or air and blood). Although the morphologies of gas exchangers differ greatly, certain shared structural and functional features exist. For example, in all cases, the transfer of O 2 and CO 2 across the water/air-blood (tissue) barriers occurs entirely by passive diffusion along concentration gradients. In the multicellular organisms, gas exchangers have developed either by evagination or invagination. The arrangement, shape, and geometries of the airways and the blood vessels determine the transport and exposure of the respiratory media and, consequently, gas exchange. The thickness of the water/air-blood (tissue) barrier, the respiratory surface area, and volume of pulmonary capillary blood are the foremost structural parameters which determine the diffusing capacity of a gas exchanger for O 2 . In fish, stratified design of the gills and internal subdivision of the lungs increase the respiratory surface area: the same adaptive property is realized by different means. A surface active phospholipid substance (surfactant) lines the respiratory surface. Adaptive specializations of gas exchangers have developed to meet individual survival needs.

Bioengineering Aspects in the Design of Gas Exchangers, 2011

The quality of a system depends on the quality of the components which form it, as well as the excellence of its organization.

Experimental Physiology, 2010

The traditional dogma has been that all gases diffuse through all membranes simply by dissolving in the lipid phase of the membrane. Although this mechanism may explain how most gases move through most membranes, it is now clear that some membranes have no demonstrable gas permeability, and that at least two families of membrane proteins, the aquaporins (AQPs) and the Rhesus (Rh) proteins, can each serve as pathways for the diffusion of both CO2 and NH3. The knockout of RhCG in the renal collecting duct leads to the predicted consequences in acid–base physiology, providing a clear‐cut role for at least one gas channel in the normal physiology of mammals. In our laboratory, we have found that surface‐pH (pHS) transients provide a sensitive approach for detecting CO2 and NH3 movement across the cell membranes of Xenopus oocytes. Using this approach, we have found that each tested AQP and Rh protein has its own characteristic CO2/NH3 permeability ratio, which provides the first demonst...

Bioengineering Aspects in the Design of Gas Exchangers, 2011

Amongst animals, diversity of form and environmental circumstances has given rise to a multitude of different adaptations subserving the relatively unified patterns of cellular metabolism. Nowhere else is this state of affairs better exemplified than in the realm of respiration.

Encyclopedia of Fish Physiology, 2011

P 50 The oxygen partial pressure at half-maximal oxygen saturation of blood or hemoglobin. Partial pressure The pressure that one gas would have if it alone occupied the same volume at the same temperature as the mixture. Root effect Property of hemoglobins in some fishes such that, in the presence of acid, it is impossible for hemoglobin molecules to be completely saturated with oxygen, even at extremely high oxygen partial pressures. Venous Adjective pertaining to blood that has passed through tissues having had some oxygen removed for metabolism.

Zoophysiology, 1998

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