IB Biology SL

Revision Notes

6.2.1 The Blood System: History

Discovery of the Circulation of Blood

Galen’s theories about blood and circulation

  • Galen was a Greek philosopher and surgeon who developed the following theories about blood and circulation
    • Blood is formed in the liver from ingested food
    • Blood is pumped backwards and forwards between the liver and the right ventricle in the heart
    • Some blood moves into the left ventricle through invisible pores and mixes with air from the lungs
    • This mixing of air with blood produces spirits which are distributed to the body via the brain
    • Blood is consumed by the tissues so that new blood must be continuously made

NOS: Theories are regarded as uncertain

William Harvey’s theories

  • William Harvey was an English Physician who overturned Galen’s theories about blood and circulation through a series of experiments and observations
  • Harvey developed the following theories (which were ridiculed at the time
    • Blood is pumped to the brain and body by the heart
    • Blood circulates through the pulmonary and systemic circulations
    • Capillaries exist which link arteries to veins
    • The liver was not capable of producing enough blood to support the idea that blood is consumed by the tissues

Discovery of the Heart as a Pump

  • Harvey used a series of experiments to show that blood flow is unidirectional and that the presence of valves prevents backflow in veins
    • Harvey attached a tourniquet to a persons upper arm and instructed them to grip tightly onto a pole
    • Once the veins became visible, Harvey proceeded to apply pressure to the veins systematically to show how blood flow was affected
    • He used this method to demonstrate how blood moves unidirectionally through the veins in the arm
  • He then demonstrated how the heart acts as a pump which forces blood out through the arteries, it then circulates around the body before it returns to the heart through the veins
  • He also showed that the blood being pumped out of the heart was travelling too quickly to have been produced by the liver (as suggested by Galen)
  • Despite not having advanced enough equipment to visualise the capillaries, Harvey predicted their presence as small vessels which link the arteries to the veins
Close

Join Save My Exams

Download all our Revision Notes as PDFs

Try a Free Sample of our revision notes as a printable PDF.

Join Now
Already a member?
Go to Top