Functional Significance of the Crocodilian Cardiopulmonary System

数百年来，鳄鱼爬行动物独特的心肺系统一直吸引着生物学家的兴趣。然而，这个系统的许多功能的功能意义仍然是一个谜。本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。与哺乳动物不同的是，哺乳动物只有一条起源于左心室的主动脉，将富含氧气的血液从心脏输送到身体，而鳄鱼有两条主动脉。其中一条主动脉起源于左心室，与哺乳动物的主动脉相似。然而，鳄鱼也有第二个主动脉，起源于右心室，终止于胃。鳄鱼分流指的是一种血液流动模式，在这种模式下，缺氧的全身静脉血液被引导到主动脉送到胃，而不是引导到肺动脉送到肺。这项研究将检验关于这种心血管系统的两个假设：(1)鳄鱼的双主动脉系统促进食物的消化；(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液流量，以及测量血气和PH值。这项研究的一个主要目的是帮助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西奥多西乌斯·多布赞斯基敏锐地说：“生物学中没有任何东西是有意义的，除非从进化的角度来看。”进化论是生物学对知识的深刻贡献。生物学的所有方面都受益于这一理论的使用，包括面向临床的生物学。只有当我们了解人类心血管系统的进化史时，才有可能在健康和疾病中充分了解人类的心血管系统。由于心血管系统是由软组织组成的，在化石记录中没有保存得很好，因此对心血管系统进化的大多数见解来自于比较不同现存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具有与典型爬行动物相似的心血管系统，例如在蜥蜴和海龟身上发现的爬行动物。鳄鱼的心血管系统是独一无二的，因为它有许多与哺乳动物相同的特征(例如，由冠状循环支持的完全分离的心室)，但也有许多其他典型爬行动物的特征(例如，两个主动脉，关闭流向肺的血液并将血液重新引导到身体的能力)。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特殊的机会，让他们深入了解哺乳动物系统是如何以及为什么从爬行动物模式进化而来的。

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.