Geert Kleinnibbelink

Chapter 1 12 The cardiovascular system The circulation of blood through the human body as we know it today, with the heart as a central pump that propels the blood through the body and ultimately returns in the heart, was described first by the English Physician Sir William Harvey (1578-1657). In 1628, Sir William Harvey published the book exercitatio anatomica de motu cordis et sanguinis in animalibus (“On the motion of the heart and blood in animals”) where he described his research and experiments. 1 Before publication of this landmark book, the Ancient Greeks including Hippocrates and Galenus viewed the cardiovascular system as comprising two distinct networks of arteries and veins. 2 A long-adhered view was introduced by Claudius Galenus around 160 AC, who hypothesised that the liver produced blood that was transported through the body, whereas air was absorbed from the lung into the pulmonary veins and carried by arteries to the various tissues of the body ( Figure 1A ). The arteries also contained blood, whereas the blood passes from the venous side via invisible pores in the interventricular septum. Blood was not seen to circulate but rather to slowly ebb and flow. This hypothesis was acknowledged for over fifteen centuries until Sir William Harvey provided evidence for his hypothesis, using simple calculations and non-invasive experiments that only required a ligature. 1 His description of the “motion of the heart and blood” is still considered valid nowadays. Harvey described, based on his experiments, that blood circulates through a closed loop system consisting of a pulmonary and systemic circulation where the heart acts as mechanical force to foresee the movement of blood ( Figure 1B ). As introduced by Harvey, the primary function of the cardiovascular system is to deliver nutrients and oxygen to tissues and removing carbon dioxide and other wastes. 2 The heart consists of a right and a left side, each consisting of an atrium and ventricle, which serves the pulmonary and systemic circulation of blood respectively. 3, 4 Once the nutrients and oxygen are delivered to peripheral tissues and organs, and when carbon dioxide and other wastes are taken up from the tissues via the capillaries, deoxygenated blood flows back to the heart via the venous system and enters the right atrium (RA) via the vena cava inferior and superior. During the diastolic phase, the right ventricle (RV) relaxes, causing the pressure in the RV to become lower than the RA, which leads to opening of the tricuspid valve and blood flows into the RV. During the systolic phase, the RV contracts