Discovery of the Circulation of Blood
NOS: Theories are regarded as uncertain; William Harvey overturned theories developed by the ancient Greek philosopher Galen on movement of blood in the body
- A theory can be defined as:
- A carefully thought-out idea, with accompanying evidence, that explains observations of the natural world
- There is always a level of uncertainty when using scientific methods
- Uncertainty can be due to
- Natural variability of individual organisms
- Accuracy of measurements taken
- Galen was an ancient Greek philosopher and surgeon who developed the following theories
- 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
- Galen failed to present any evidence for his theories
- 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 circulation systems
- Capillaries exist which link arteries to veins
- Blood flow is too fast for blood to be consumed by the tissues; it would run out too quickly to be replaced. Instead, blood returns to the heart and re-circulates
- Harvey refused to accept Galen's theories without direct evidence and he toured Europe to demonstrate evidence for his own theories to others, eventually leading to acceptance of his new theories
Galen proposed a model which was later disproved by William Harvey
