History Weblecture for Unit 24
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Anatomy focuses on structures. It asks questions like: "What tissues are there? How doe they compose organs? Which organs are part of which systems?" This last question is not as easy to answer as one might think, since some organs, like the liver, are part of several systems when we look not only at how they are connected to one another, but also at how they function together.
The study of the functions of tissues, organs, and organ systems is the study called physiology. Of course, in practical terms, it isn't possible to completely separate the two studies, but there are times when we focus on "what is it" (anatomy) more than on "what does it do" (physiology). The kind of question we ask is important, because it influences the kind of observations we make, data we collect, and the analysis of that data to answer a specific question. In this unit, we look at how the study of the function of the heart changed our understanding of human biology.
Pulmonary circulation, from the heart to the lungs, and back to the heart, was first described by the Spanish theologian and physician Michael Servetus, but his description was contained in his theological work, Christianismi Restitutio. Servetus was however, denounced in Spain as a heretic and fled to Geneva, where his radical ideas rejecting the Trinity were intolerable to the Protestants as well, and he was eventually executed there for heresy, his books were destroyed, and his theory of pulmonary circulation vanished. Like Leonardo's anatomical drawings, his work had little impact on his contemporaries.
A century after the anatomical drawings of Vesalius appeared in print, the English physician William Harvey carefully observed human and animal bodies and put together a theory of the function of the heart and the circulation of the blood. He was one of a new kind of biological researcher--one grounded in the logic of the Renaissance, with its emphasis on observation rather than reliance on the authority of ancient authors. He was also aided by the new mechanical view of the universe which was developing from the works of Copernicus, Kepler, Galileo, and Newton.
William Harvey was born in 1578 and entered Cambridge University at the age of 15, where he studied the arts program for four years before travelling to universities in France, Germany, and Italy to complete his medical education. In 1599 he enrolled in the medical school at Padua. Vesalius' new anatomy had been accepted for some time, but certain theories of Galen's concerning the functions of different organ systems were still popular. However, Padua was used to new ideas -- it was the university Copernicus had attended a century earlier to study medicine, and among its faculty in Harvey's time was Galileo Galilei, introducing new ideas on mechanics, and Heironymus Fabricius, a physician who had observed valves in human veins but was debating whether or not to publish his findings. Harvey completed his degree in medicine in 1602 and returned to England, where he became a fellow of the College of Physicians in London and head physician of St. Bartholomew's Hospital, an institution founded by a Norman monk in 1123, which still exists today to serve the people of the Smithfield district in London.
In 1618, Harvey became physician to James I, King of England. He was apparently not a very good practical doctor, but being part of the King's household gave him sufficient income that he was able to pursue his research into the circulation of the blood. In 1628, he published his book on the movement of the heart and blood, and started a major controversy which lasted until after his death.
Harvey based his theory that the blood circulates through the heart and back to it in a closed system on both observation and logic. He noticed that the heart tissue looks like muscle and contracts like muscles do. Galen had proposed that the arteries also contract on their own to pump blood, but Harvey noticed that the arteries dilate (expand) only with the heartbeat, so he assumed that the arteries expanded to accommodate surges of blood through them. Harvey also noticed that the heart doesn't beat as a unit, but that the upper and lower parts contract at different times. He traced the flow of blood into the top right chamber, called the right atrium, and into the lower right chamber, the right ventricle. He discovered the valves between the two chambers kept the blood from flowing backwards into the right atrium as the lower chambers contracted. Instead, the right ventricle pushed the blood out of the heart through a pulmonary artery to the lungs. The blood returned from the lungs through a large vein and entered the upper left chamber, the left atrium, was pushed into the lower left chamber, the left ventricle, when the upper chambers contracted, and then was pushed out of the heart through the aorta and into the body.
Much of this was already known when Harvey began his researches, but Harvey added one new observation to the studies that had been done earlier. Based in Galileo's theories of mechanics and hydraulics, Harvey calculated that the volume of blood pumped out of the heart was over 2 ounces of liquid per heart beat. He did some calculations and realized that the heart pumped three times the weight of a grown man every hour. There was no possible way that the veins or any other system could manufacture that much blood every hour, much less every day for an entire lifetime. The blood coming into the heart through the vein into the right atrium had to be the same blood that was pumped out of the heart some time earlier--the heart, arteries, and veins had to form a closed system. It was this theory which Harvey published in his 1628 De Motu Cordis, On the Movement of the Blood. Being acutely attuned to the fact that his work attacked Galen, the initial publication occurred not in England, but in Franfurt, Germany, and because he did not oversee the printing, it had many errors, which had to be corrected in later editions.1
Study this illustration on the circulation of the blood in the arm from Harvey's text.
Read Harvey's description Of the Quantity of Blood Passing Through the Heart From the Veins to the Arteries; and of the Circular Motion of the Blood. (This is an excerpt from chapter VIII of his book. You do not need to read the entire webpage unless you wish.)
There was one important point missing from Harvey's theory, however: he could not show how the arteries were connected to the veins. Dissections revealed only that the arteries got smaller and smaller until they became unobservable, and the veins started as small tubes which joined together to form one great tube flowing into the body. Although Harvey believed there had to be a connection, he could not point to any observations to prove it.
On the death of King James in 1632, Harvey became physician to James' son, Charles I, but with his new king came devastating political consequences. In 1649, Parliament voted to execute Charles I for treason. Although he was in retirement, Harvey's prior association with the royal household made his situation difficult. Not only was his house vandalized and his papers burned, his books were scorned by those who opposed the Royalists. Harvey died in 1657 with the controversy over his circulation theory still raging.
Four years after Harvey's death, Maricello Malpighi of Bologna in Italy used the a microscope to examine the circulation of the blood in animal tissue, and observed and documented the existence of capillaries, tiny vessels which connected the small arteries with the small veins.
1 Although I checked a number of sources, I have not been able to find any primary materials containing contemporary criticism of Harvey's work. Apparently, so thoroughly has he now been accepted that his opponents' words have vanished into history.
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