The Heart and the Circulatory System

IntroductionAnatomy of the Heart Circulatory SystemBlood VesselsBlood Supply Problems

Introduction Imagine that you are living in the year 1535, and that you don't feel well. You have had some problems with fatigue, feeling a little more tired than usual when you walked to the market and back. You tell this to your physician, and he sends you to another physician down the street, telling you there may be some problem with your circulation. When you get to the new physician, he tells you to take off your shirt and lie down on the bench. After a quick look in your mouth, he says your vital blood is probably O.K. But he's concerned that maybe your nutritive blood is not being made fast enough. Then he starts to feel around on your abdomen. He mentions that your liver is slightly enlarged and suggests that maybe you have not been eating enough green leafy vegetables or protein. Wait a minute! You have come in with problems with your circulation, and this guy is talking about your liver and the type of foods you have been eating! What is going on here? Where did this fellow learn to practice medicine anyway? Confusion over the nature of the heart, the blood, and the role of the blood in the body had existed for centuries. Pliny the Elder, a Roman writer who lived from AD 23-79, and author of a 37-volume treatise entitled Natural History, wrote "The arteries have no sensation, for they even are without blood, nor do they all contain the breath of life; and when they are cut only the part of the body concerned is paralyzed...the veins spread underneath the whole skin, finally ending in very thin threads, and they narrow down into such an extremely minute size that the blood cannot pass through them nor can anything else but the moisture passing out from the blood in innumerable small drops which is called sweat." A century later Galen, a Greek physician who lived in the second century AD., spent his lifetime in observation of the human body and its functioning. Galen believed and taught his students that there were two distinct types of blood. 'Nutritive blood' was thought to be made by the liver and carried through veins to the organs, where it was consumed. 'Vital blood' was thought to be made by the heart and pumped through arteries to carry the "vital spirits." Galen believed that the heart acted not to pump blood, but to suck it in from the veins. Galen also believed that blood flowed through the septum of the heart from one ventricle to the other through a system of tiny pores. He did not know that the blood left each ventricle through arteries. Physicians, as well as citizens, of many cultures had their own beliefs concerning the nature of the heart and circulatory system. While the Greeks believed that the heart was the seat of the spirit, the Egyptians believed the heart was the center of the emotions and the intellect. The Chinese believed the heart was the center for happiness. Even our modern society continues to put emotions under the control of the heart, speaking of having a broken heart when a loved one leaves, or stealing one's heart around Valentine's Day. These beliefs continued to be taught and taken as law until an English physician named William Harvey challenged them in the late 1620's. William Harvey was born in 1578 in Folkstone, England. The eldest of seven sons, Harvey received a Bachelor of Arts degree from Cambridge in 1597. He then studied medicine at the University of Padua, receiving his doctorate in 1602. By all measures, Harvey was successful. After he finished his studies at Padua, he returned to England and set up practice. He then married Elizabeth Brown, daughter of the court physician to Queen Elizabeth I and King James I. This put in him in position to be noticed by the aristocracy, and Harvey quickly moved up the ladder. Eventually, he became court physician to both King James I and King Charles I. While acting as court physician, Harvey was able to conduct his research in human biology and physiology. Harvey focused much of his research on the mechanics of blood flow in the human body. Most physicians of the time felt that the lungs were responsible for moving the blood around throughout the body. Harvey questioned these beliefs and his questions directed his life-long scientific investigations. Harvey did not let the beliefs of Galen concerning the role of natural, vital, and animal spirits and their effects on physiology affect his objectivity. Instead, Harvey asked simple, pointed questions, the types of questions that even today are the hallmark of good scientific research. Harvey asked such questions as why did both the lungs and the heart move if only the lungs were responsible for causing circulation of blood? Why should, as Galen suggested, structurally similar parts of the heart have very different functions? Why did 'nutritive' blood appear so similar to 'vital' blood? These, and other, questions gave Harvey his focus. Harvey's lecture notes show that he believed in the role of the heart in circulation of blood through a closed system as early as 1615. Yet he waited 13 years, until 1628, to publish his findings in his work Exercitatio anatomica de motu cordis et sanguinis in animalibus or On the Movement of the Heart and Blood in Animals. Why did he wait so long? Galenism, or the study and practice of medicine as originally taught by Galen, was almost sacred at the time Harvey lived. No one dared to challenge the teachings of Galen. Like most physicians of his day, William Harvey, was trained in the ways of Galen. Conformation was not only the norm, but was also the key to success. To rebel against the teachings of Galen could quickly end the career of any physician. Perhaps this is why he waited. Harvey's hesitation proved well-founded. After his work was published, many physicians and scientists rejected him and his findings. Using different assumptions of the amount of blood contained in the heart, scientists argued that the blood could indeed be consumed. Controversy raged for a full twenty years after publication of "On the Movement of the Heart and Blood in Animals." Yet, with time, more and more physicians and researchers accepted Harvey's hypotheses. Like all good research, Harvey's work raised more questions than it answered. For example, if blood was not consumed by organs, how did different parts of the body obtain nourishment? If the liver did not make blood from food, where did blood originate? These questions, and others like them, directed the research of many investigations for many years to come. Medical practice in Harvey's time, however, changed little. Even though the mechanics of blood flow were understood now, the understanding of the causes of many diseases were still bathed in the mystery of spirits. In fact, the practices of bleeding, lancing, and leeching increased in the years following Harvey's work. On the positive side, medicine did make some advances, for it was during the seventeenth century that administering medicine through intravenous injections came into practice. William Harvey's classic work became the foundation for all modern research on the heart and cardiovascular medicine. It has been said that Harvey's proof "of the continuous circulation of the blood within a contained system was the seventeenth century's most significant achievement in physiology and medicine." Further, his work is considered to be one of the most important contributions in the history of medicine. Without the understanding of the circulatory system made possible by Harvey's pioneering work, the medical miracles that we think are commonplace would be impossible. Let's take a few moments to discuss the hearts and circulatory systems found in a variety of animals.