William Harvey’s description of the circulatory system could not explain how blood moved from arteries to veins. This was one of the mysteries solved by the invention of the microscope.
In 1661, Marcello Malpighi was working in Bologna, Italy when he discovered tiny vessels through which blood travels. These tiny vessels known as capillaries could only be seen using a microscope and they proved to be the missing element in Harvey’s theory.
Capillaries are the smallest blood vessels in the human body which function as the site of exchange for many substances. While substances such as water, oxygen and glucose exit the body, other items including, water, carbon dioxide, uric acid, lactic acid, urea and creatine enter the bloodstream through capillaries.
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