William Harvey was a 17th century English physician who showed that blood moves in a continuous circulation through the body. Before his work, many physicians followed ancient ideas that blood was made in the liver and used up by the organs. Harvey used observation, measurement, animal dissection, and simple experiments to argue that the heart acts as a pump.
His discovery became a foundation of modern physiology and changed how doctors understood the body.
Key Facts
- William Harvey published De Motu Cordis in 1628, explaining that blood circulates through the body.
- The heart works as a pump that sends blood through arteries and receives blood back through veins.
- Cardiac output can be estimated by CO = stroke volume × heart rate.
- One-way valves in veins help blood return toward the heart and prevent backward flow.
- Harvey inferred capillaries before they were directly observed, because arteries and veins had to be connected in a closed loop.
- Blood flow depends on pressure difference and resistance, often summarized as Q = ΔP/R.
Vocabulary
- Circulation
- Circulation is the continuous movement of blood through the heart, lungs, arteries, capillaries, and veins.
- Artery
- An artery is a blood vessel that carries blood away from the heart.
- Vein
- A vein is a blood vessel that carries blood back toward the heart.
- Valve
- A valve is a structure that opens in one direction to keep blood flowing forward.
- Cardiac output
- Cardiac output is the amount of blood the heart pumps in one minute.
Common Mistakes to Avoid
- Saying arteries always carry oxygen-rich blood is wrong because pulmonary arteries carry oxygen-poor blood from the heart to the lungs.
- Thinking Harvey saw capillaries directly is wrong because microscopes later allowed Marcello Malpighi to observe capillaries after Harvey had already inferred their existence.
- Treating blood as something the body constantly uses up is wrong because Harvey showed that the same blood recirculates through a closed system.
- Ignoring vein valves is wrong because Harvey used their one-way action as evidence that venous blood flows back toward the heart.
Practice Questions
- 1 A heart pumps 70 mL of blood per beat and beats 75 times per minute. What is the cardiac output in mL/min and L/min?
- 2 If a patient has a cardiac output of 5.6 L/min and a heart rate of 80 beats per minute, what is the stroke volume in mL per beat?
- 3 Explain how Harvey could use a ligature on an arm and the direction of vein valves to support the idea that blood flows back toward the heart.