How was pulmonary circulation understood before William Harvey described full circulation?

Before William Harvey described the full circulatory system, the understanding of blood flow was dominated by the physiological theories of the Greek physician Galen, which persisted for over 1,400 years.1

Galen taught that the body contained two separate blood systems:
* Nutritive blood: Believed to be formed in the liver and distributed by the veins to provide nutrition to the body.21
* Vital blood: Believed to be formed in the heart and distributed by the arteries to provide life-giving energy.21

Regarding pulmonary circulation, Galen theorized that a small amount of blood seeped from the right to the left ventricle through minute, invisible pores in the heart's wall. While 13th-century physician Ibn al-Nafis correctly identified that blood must pass through the lungs to reach the left ventricle, his work remained unknown to Western science for centuries. Later, in the 16th century, Michael Servetus and Matteo Realdo Colombo also described this "lesser circulation," but the concept of blood circulating throughout the entire body was not established until Harvey’s work.12345