Key Terms You Must Know

📖 Key Terms You Must Know

William Harvey (1578-1657)

English physician who proved that blood circulates around the body, pumped by the heart, in a continuous loop. Trained at Padua University (where Vesalius had worked). Published De Motu Cordis (On the Motion of the Heart and Blood) in 1628. Used a combination of dissection, observation of valves, and mathematical calculation of heart output to disprove Galen's theory that blood was produced in the liver and consumed by organs. His work was initially rejected by many physicians but was eventually accepted by around 1700.

Circulation of the blood

Harvey's discovery that blood travels in a continuous circuit around the body: pumped from the heart through arteries to the body's organs and tissues, then returning to the heart through veins. The heart acts as a pump, not (as Galen believed) simply as a warming organ. This contradicted 1,400 years of Galenic medicine. Harvey could not explain how blood moved from arteries to veins in the tissues — the capillaries were not discovered until Malpighi in 1661.

De Motu Cordis (1628)

Harvey's published work, translated as On the Motion of the Heart and Blood in Animals. It contained his mathematical proof of circulation, his observations of valves in veins, and detailed diagrams of his experiments. Published via the printing press, it spread across Europe. Like Vesalius's 1543 book, its publication made the ideas unstoppable even in the face of opposition. The year 1628 is a key date in the history of medicine.

Capillaries

The tiny blood vessels connecting arteries to veins in the body's tissues. Harvey correctly predicted their existence — his theory required some connecting link between arteries and veins — but he could not see them because his microscopes were not powerful enough. Marcello Malpighi discovered capillaries in 1661 using a more powerful microscope, completing Harvey's theory and removing the final objection to it. This dependency on microscope technology shows how one scientific advance depends on technological development in adjacent fields.

Valves

One-way gates inside veins that prevent blood from flowing backwards. Harvey observed that valves in veins only allowed blood to flow towards the heart, not away from it. This was a crucial piece of evidence: if blood could only flow one way in veins (towards the heart), it must be circulating rather than simply being produced and consumed. Galen's theory required no valves — he believed blood flowed outward from the heart through both arteries and veins. The existence of valves directly contradicted this.