Dissertation Research: Did Lungs and Intracardiac Shunting Evolve to Oxygenate the Heart?

9423297杰克逊：给心肌提供充足的氧气对于正常的心脏功能是必不可少的。在哺乳动物中，冠状动脉将氧气充足的血液输送到心肌。冠状动脉阻塞导致的心肌氧气不足是人类死亡的主要原因，这一事实说明了它们的重要性。心肌的氧合对非哺乳动物动物也很重要，可能对脊椎动物心血管系统的进化产生了重大影响。与哺乳动物不同，鱼、两栖动物和爬行动物的心脏没有通往心肌的动脉循环。相反，流经心腔的静脉血液提供海绵状心肌所需的氧气。这在运动中造成了一个问题，它既增加了心脏的氧气需求，又降低了返回心脏的静脉血液中的氧气水平。这项研究将检验这一假设，即选择维持心脏供氧和性能导致脊椎动物心血管系统的两项重大创新：1)肺的进化；2)陆地爬行动物和两栖动物心脏内分流的持久性，这允许从肺中含氧的血液与从组织中返回的低含氧血液的混合。这项研究将确定低等脊椎动物心脏的需氧量，并确定肺通风、心内分流和冠脉循环作为满足这些需求的机制的相对重要性。如果中心假说是正确的，它将为肺的进化带来一个新的范式，并有助于解释温带脊椎动物复杂心血管系统的持久性。这一结果可能会改变传统的观点，即现代动物的心脏解剖学是由于选择了改善向体循环输送营养的创新而导致的，而没有认识到输送营养对心脏本身的重要性。

9423297 Jackson An adequate supply of oxygen to heart muscle is essential to normal cardiac function. In mammals, the coronary arteries carry well-oxygenated blood to the heart muscle. Their importance is illustrated by the fact that insufficient oxygenation of heart muscle due to obstruction of the coronary arteries is a leading cause of death in humans. Oxygenation of heart muscle is also important for non- mammalian animals, and may have had a major impact on the evolution of the vertebrate cardiovascular system. In contrast to mammals, the hearts of fish, amphibians and reptiles have no arterial circulation to the heart muscle. Instead, venous blood flowing through the heart chambers supplies the oxygen needs of the spongy cardiac muscle. This poses a problem during exercise, which both increases cardiac oxygen demand and decreases oxygen levels in venous blood returning to the heart. This research will test the hypothesis that selection for maintaining cardiac oxygen supply and performance led to two major innovations in the cardiovascular systems of vertebrates: 1) the evolution of lungs and 2) the persistence in terrestrial reptiles and amphibians of the intracardiac shunt, which permits mixing of oxygenated blood from the lungs with poorly oxygenated blood returning from the tissues. This research will establish the oxygen requirements of the hearts of lower vertebrates and determine the relative importance of lung ventilation, intracardiac shunting and coronary circulation as mechanisms to meet those requirements. If the central hypothesis is correct, it will lead to a new paradigm for the evolution of lungs and help explain the persistence of the complex cardiovascular systems of ectothermic vertebrates. The outcome may alter the traditional view that the cardiac anatomy of modern animals has resulted from selection for innovations that improve nutrient delivery to the systemic circulation, without recognition of the importance of nutrient delivery to the heart itself.