1. Circulation of Blood: Harvey's most significant contribution was his discovery of the circulation of blood in the human body. Before his time, it was believed that blood ebbed and flowed in the body without a defined pathway. Harvey conducted experiments and observations, using dissections and vivisections, to demonstrate that blood flows in a continuous circuit, pumped by the heart through the arteries and veins.
2. Function of the Heart: Harvey also expanded our understanding of the heart's function. He showed that the heart's contraction (systole) actively propels blood out of the ventricles into the arteries, and that the heart's relaxation (diastole) allows blood to fill the ventricles from the atria. This led to the understanding of the heart's role as a pump.
3. Structure of Blood Vessels: Harvey's studies also shed light on the structure and function of blood vessels. He observed the presence of valves in the veins, which prevent backflow of blood and aid in maintaining blood pressure. Additionally, he described the concept of arterioles and venules, smaller branches of arteries and veins, which are crucial for the distribution and regulation of blood flow throughout the body.