How blood circulates is a mystery that was solved
by an English physician William Harvey, in the seventeenth century.
Harvey was a medical graduate from the University of Padua. From
among all his lessons during his medical study, one particular fact
stuck to his mind and probably kept triggering him into thinking all
the time. He knew that veins had valves that permitted blood to
travel in only one direction. However, the question that plagued him
was, what was the exact role of veins in the human body?
Until this time, it was
believed that the liver produced the body’s blood supply and that it
pumped the blood through the body too. This was a claim made by
Galen, an eminent scientist and Harvey knew the dangers of
contradicting the scientist. Yet, he could not accept the theory.
Harvey, therefore, decided to conduct his own experiments and find
out the validity of the claim.
Harvey decided to study
the flow of blood by operating on live animals. For twelve years, he
conducted his experiments before members of the Royal College of
Physicians in London, England. The members however, continued their
support to Galen’s theory and questioned Harvey’s ideas.
Finally, in a series of
brilliant experiments on animals and humans, Harvey demonstrated how
blood circulates in the body. He proved that when an artery was
blocked, the veins draining this artery collapsed. When a vein was
blocked, it swelled below the blockage and collapsed above it, but
the swelling disappeared when the blockage was removed. He also
showed that the valves in the veins allowed blood to flow only in
the direction of the heart. Together, these discoveries proved
Harvey’s claim that blood moves in a circle in the body right.
This discovery is
regarded as the single greatest achievement of all times. It also
established the principle of doing experiments in medicine to learn
how the body’s organs and tissues function.
Anatomical Essay on the Motion of the Heart and Blood in Animals,
published in the year 1628, inspired other like minded scientists to
conduct research on the mechanical functions of many bodily
processes, including respiration, digestion, metabolism, and
reproduction. In the eighth chapter of his book, he carefully
introduced the revolutionary idea that blood goes in a circle in the
body, traveling from the heart to the arteries to the veins and
back to the heart. He devoted the remaining chapters of his book to
proving that he was right.
We now know that if we
were to trace a drop of blood as it circulated through the body, the
course it would follow would be like this. The blood with oxygen
from the lungs would go to the left auricle, then to the left
ventricle and from there on to the aorta. From here, it would be
carried by the great artery and its branches to the various parts of
the body. Through capillaries, it will go from the arteries to the
veins, which will become larger. From here on, it will reach the
right auricle and then the right ventricle. From here, it will go to
the artery, to be carried to the lungs. At this stage, it will give
up carbon dioxide and water and take oxygen. It is now ready to go
back to the left auricle of the heart for yet another journey.
Scientists have now established that the heart squeezes and relaxes
about 100,000 times each day and pumps 3,600 gallons of blood in
twenty-four hours in an adult male.