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

小杰克逊9423297 向心肌提供充足的氧气对正常的心脏功能是必不可少的。 在哺乳动物中，冠状动脉将充分含氧的血液输送到心肌。 由于冠状动脉阻塞导致的心肌氧合不足是人类死亡的主要原因，这一事实说明了其重要性。 心肌的氧合对非哺乳动物也很重要，并且可能对脊椎动物心血管系统的进化产生重大影响。 与哺乳动物不同，鱼类、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，流经心室的静脉血供应海绵状心肌所需的氧气。 这在运动期间造成了一个问题，这既增加了心脏的需氧量，又降低了返回心脏的静脉血中的氧含量。 这项研究将检验一个假设，即维持心脏供氧和性能的选择导致脊椎动物心血管系统的两个主要创新：1）肺的进化和2）陆地爬行动物和两栖动物心内分流的持续存在，其允许来自肺的氧合血液与从组织返回的氧合不良的血液混合。 这项研究将建立低等脊椎动物心脏的氧气需求，并确定肺通气、心内分流和冠状动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，它将为肺的进化提供一个新的范式，并有助于解释肺的持续存在。 复杂 心血管 系统 的 变温脊椎动物 这一结果可能会改变传统的观点，即现代动物的心脏解剖结构是由于选择了改善营养输送的创新， 体循环，而不认识 向心脏输送营养的重要性

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.