Genetic Regulation of Angiogenesis and Lymphangiogenesis: Visualization and characterization of the vasculature

Aelius Galenus (AD 129 – 199) was one of the first persons to explore the blood vasculature. During his work as physician and surgeon, he recognized distinct differences in blood vessels. During surgery, he observed that vessels were filled with either dark or bright blood. He believed that the human blood vascular system contained two one-way blood distribution routes. The dark (venous) blood was generated directly from food uptake in the liver, whereas the bright (arterial) blood was generated in the heart. From the heart and liver, blood was then equally distributed and ‘consumed’ by all other organs in the body. To complete the vascular system, blood was then regenerated in either the heart or liver (reviewed in (Carmeliet, 2005). This ‘two-one way circulation’ theory was believed for centuries and it was only until the 16th century that the British biologist and medical doctor William Harvey could show that Galenus was wrong. Harvey characterized and quantified the blood volume which passes the heart and concluded that this was much larger than the amount of blood that could be generated by the body itself (On the Motion of the Heart and Blood in Animals, 1628, William Harvey). Harvey postulated that there had to be a circulatory loop in the body which consisted of the heart and a connected vessel system. With a simple experiment, by tightening a ligature on to the upper arm of an individual, he indeed identified a circulatory loop which was connected to the heart and identified the presence of arteries and veins but also functional differences between arteries and veins (On The Motion Of The Heart And Blood In Animals, 1628, William Harvey, (Carmeliet, 2005).

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