Galen's theory of blood flow, which persisted for over a millennium, had a significant impact on the historical understanding of the circulatory system. Here's a summary of his key ideas:
- Blood origin: He believed the liver, not the heart, was the source of blood, which was produced from digested food.
- Blood flow: Blood flowed in a one-way, centrifugal manner, meaning it moved outwards from the liver through the veins and was then consumed by the body's tissues.
- No circulation: There was no concept of blood continuously circulating throughout the body.
- Two blood types: Galen distinguished between two types of blood:
- Venous blood: Carried nutrients from the liver to the body.
- Arterial blood: Contained air or "pneuma" essential for life, but not derived from the lungs.
- Invisible pores: He proposed the existence of invisible pores in the heart's septum allowing some blood to pass from the right ventricle to the left.
It's important to note that while Galen's theory held sway for a long time, it was ultimately proven inaccurate. The discovery of the pulmonary circulation by William Harvey in the 17th century revolutionized our understanding of blood flow and paved the way for further advancements in cardiovascular medicine.
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