Functional Significance of the Crocodilian Cardiopulmonary System

数百年来，生物学家一直对鳄鱼类爬行动物独特的心肺系统感兴趣。然而，这个系统的许多特性的功能意义仍然是一个谜。本文提出的研究旨在了解鳄鱼双主动脉（左、右）和心血管分流的功能意义。哺乳动物只有一条主动脉，起源于左心室，将富含氧气的血液从心脏输送到身体，而鳄鱼不同，它们有两条主动脉。一条主动脉起源于左心室，与哺乳动物的主动脉相似。然而，鳄鱼也有第二条主动脉，起源于右心室，止于胃。鳄鱼分流指的是一种血流模式，在这种血流模式中，缺氧的全身静脉血被引导到主动脉，然后被送到胃，而不是被引导到肺动脉，然后被送到肺部。这项研究将测试关于这种心血管系统的两个假设：(1)鳄鱼的双主动脉系统有助于食物的消化；(2)该系统在运动后维持适当的血液pH值。它将包括使用超声波技术测量血流量和测量血气和ph值。这项研究的一个主要目的是有助于我们理解脊椎动物心血管系统的进化。著名的进化生物学家狄奥多西·多布赞斯基（Theodosius Dobzhansky）敏锐地说：“生物学中没有任何东西是有意义的，除非从进化的角度出发。”进化论是生物学对知识的深刻贡献。生物学的各个方面都受益于这一理论的应用，包括临床导向的生物学。只有了解了心血管系统的进化史，我们才能全面了解健康和疾病状态下的心血管系统。因为心血管系统是由软组织组成的，在化石记录中保存得不好，所以对心血管系统进化的大多数了解都来自于比较不同脊椎动物的心血管特征和功能。哺乳动物的早期祖先几乎肯定有一个类似于典型爬行动物的心血管系统，比如蜥蜴和海龟。鳄鱼的心血管系统是独一无二的，因为它与哺乳动物有许多共同的特征（例如，由冠状动脉循环支持的完全分离的心室），但也有许多其他典型的爬行动物特征（例如，两条主动脉，能够关闭血液流向肺部并将血液重新输送到身体）。因此，在鳄鱼身上发现的“哺乳动物”和“爬行动物”特征的矛盾组合为科学家提供了一个难得的机会，可以深入了解哺乳动物系统如何以及为什么从爬行动物模式进化而来。

The unique cardiopulmonary system of crocodilian reptiles has interested biologists for hundreds of years. Yet the functional significance of many features of this system remains a mystery. The research proposed herein seeks to understand the functional significance of the dual aortas (left and right) and cardiovascular shunt of crocodilians. Unlike mammals, that have only one aorta that originates in the left ventricle and carries oxygen-rich blood from the heart to the body, crocodilians have two aortas. One aorta originates from the left cardiac ventricle and is analogous with the mammalian aorta. However, crocodilians also have a second aorta that originates from the right cardiac ventricle and terminates at the stomach. The crocodilian shunt refers to a blood flow pattern where oxygen-poor systemic venous blood is directed into this aorta to be sent to the stomach, rather than directed into the pulmonary artery to be sent to the lungs. The research will test two hypotheses regarding this cardiovascular system: (1) that the dual aorta system of crocodilians facilitates digestion of food and (2) that this system functions to maintain appropriate blood pH after exercise. It will consist of measurements of blood flow using ultrasonic technology and measurements of blood gases and pH. A major aim of this research is to contribute to our understanding of the evolution of the vertebrate cardiovascular system.A leading evolutionary biologist, Theodosius Dobzhansky, astutely said, "Nothing in biology makes sense except in the light of evolution." Evolutionary theory is a profound contribution of biology to knowledge. All aspects of biology have benefited from the use of this theory, including clinically oriented biology. A full understanding of the human cardiovascular system in health and in disease is only possible if we understand the evolutionary history of the system. Because the cardiovascular system is made up of soft tissues and does not preserve well in the fossil record, most insight into the evolution of the cardiovascular system comes from comparing cardiovascular features and functions of different living vertebrates. The early ancestors of mammals almost certainly had a cardiovascular system that was similar to that of a typical reptile, such as is found in lizards and turtles. The crocodilian cardiovascular system is unique because it shares numerous features with that of mammals (e.g., a completely divided cardiac ventricle supported by a coronary circulation) but has many other features that are typically reptilian (e.g., two aortas, the ability to shut down blood flow to the lung and redirect that blood to the body). Thus, the paradoxical assemblage of 'mammalian' and 'reptilian' features found within the crocodilians provides scientists with an exceptional opportunity to gain insight into how and why the mammalian system evolved from the reptilian pattern.