Science scene
The Circulation of the Blood
What we understand about the way the blood circulates around the body comes from the work of the scientist, William Harvey, who is, by the way, no relation!
arvey lived from 1578 to 1657 and was the official doctor in the courts of King James I and Charles I. He was able to obtain carcases of deer killed in the Royal hunt to study their internal organs, especially
H
their blood vessels. Thanks to Harvey’s experiments, we now know that blood is pumped away from the heart through arteries. Arteries have thick elastic walls, the blood in them is under
pressure and they have a ‘pulse’. Arteries carry blood to all parts of the body. But what happens to the blood then? In his book,
“Anatomical Essay on the Motion of the Heart and Blood in Animals” (1628), William Harvey proved that the blood moved in a closed loop away from the
heart in arteries and back again through veins.
He showed that veins have flaps inside them which act as ‘valves’. They only allow blood to flow towards the
heart. These ‘non return’ valves are necessary because the pressure of the blood in veins is low.
Towards heart
Valve open, blood flows towards the heart
Brain
William Harvey explains his
theory to the King.
Lungs
Heart
Gut
Muscles
Valve closed, preventing blood flowing backwards
You can try this yourself. Find a nice big
vein on your arm. Press down on it with a finger. Then, keeping the first finger in
place, use a second finger to push the blood in the vein towards the heart, and then let the
second finger go. Notice how the vein does not ‘fill up’ until you lift off the first finger.
6 An illustration from Harvey’s book, published in 1628
VEIN VEINS
ARTERY ARTERIES
Did You know?
Your heart beats 35 million times per year and pumps a
million barrels of blood during the average lifetime. That would fill three ocean-going oil tankers!
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