Department of Zoology, University of British Columbia, Vancouver, BC V6T 1Z4, Canada.
Department of Zoology, University of British Columbia, Vancouver, BC V6T 1Z4, Canada.
Comp Biochem Physiol A Mol Integr Physiol. 2015 Aug;186:4-26. doi: 10.1016/j.cbpa.2014.10.029. Epub 2015 Feb 16.
In response to varying environmental and physiological challenges, vertebrates have evolved complex and often overlapping systems. These systems detect changes in environmental oxygen availability and respond by increasing oxygen supply to the tissues and/or by decreasing oxygen demand at the cellular level. This suite of responses is termed the oxygen transport cascade and is comprised of several components. These components include 1) chemosensory detectors that sense changes in oxygen, carbon dioxide, and pH in the blood, and initiate changes in 2) ventilation and 3) cardiac work, thereby altering the rate of oxygen delivery to, and carbon dioxide clearance from, the tissues. In addition, changes in 4) cellular and systemic metabolism alters tissue-level metabolic demand. Thus the need for oxygen can be managed locally when increasing oxygen supply is not sufficient or possible. Together, these mechanisms provide a spectrum of responses that facilitate the maintenance of systemic oxygen homeostasis in the face of environmental hypoxia or physiological oxygen depletion (i.e. due to exercise or disease). Bill Milsom has dedicated his career to the study of these responses across phylogenies, repeatedly demonstrating the power of applying the comparative approach to physiological questions. The focus of this review is to discuss the anatomy, signalling pathways, and mechanics of each step of the oxygen transport cascade from the perspective of a Milsomite. That is, by taking into account the developmental, physiological, and evolutionary components of questions related to oxygen transport. We also highlight examples of some of the remarkable species that have captured Bill's attention through their unique adaptations in multiple components of the oxygen transport cascade, which allow them to achieve astounding physiological feats. Bill's research examining the oxygen transport cascade has provided important insight and leadership to the study of the diverse suite of adaptations that maintain cellular oxygen content across vertebrate taxa, which underscores the value of the comparative approach to the study of physiological systems.
针对不断变化的环境和生理挑战，脊椎动物进化出了复杂且经常重叠的系统。这些系统检测环境中氧气可用性的变化，并通过增加组织的氧气供应和/或降低细胞水平的氧气需求来做出反应。这一系列反应被称为氧气运输级联，由几个组成部分组成。这些组成部分包括 1）化学感受器探测器，它可以检测血液中氧气、二氧化碳和 pH 的变化，并启动 2）通气和 3）心脏工作的变化，从而改变氧气输送到组织的速度和从组织中清除二氧化碳的速度。此外，4）细胞和全身代谢的变化改变了组织水平的代谢需求。因此，当增加氧气供应不足或不可能时，可以在局部管理氧气需求。这些机制共同提供了一系列反应，有助于在面临环境缺氧或生理缺氧（例如由于运动或疾病）时维持全身氧气稳态。Bill Milsom 毕生致力于研究这些跨进化的反应，反复证明了应用比较方法解决生理问题的力量。本综述的重点是从 Milsomite 的角度讨论氧气运输级联的每一步的解剖结构、信号通路和力学。也就是说，要考虑到与氧气运输相关的问题的发育、生理和进化成分。我们还强调了一些引人注目的物种的例子，这些物种通过其在氧气运输级联的多个组成部分中的独特适应，引起了 Bill 的注意，这些适应使它们能够实现惊人的生理壮举。Bill 研究氧气运输级联的工作为研究维持脊椎动物分类群中细胞氧气含量的多样化适应提供了重要的见解和领导，这突显了比较方法在研究生理系统中的价值。
