THE HEART SYSTEM

One of the most relevant and extraordinary contributions to science in terms of accuracy and modernity is undoubtedly Leonardo's observation and description of the functioning of the heart and its system. During a brilliant experiment, Leonardo injected some melted wax into the ventricles of a human heart to give it its real shape. He understood that the right side of the heart takes the blood from the veins , while the left side carries it to the arteries.

The intuitions of the florentine genius proved to be true and were confirmed only at the beginning of the 20th century.

Before Leonardo, the heart had never been studied as a muscle; instead, it was associated with emotions and humors or linked to beliefs and superstitions.

THE CARDIO-VASCULAR SYSTEM

The human heart is located in a cavity called mediastinum, situated in the middle of the chestx between the lungs; it has more or less the size of our fist, weighs about 300 g and consists mainly of a thick layer of striated muscle tissue called myocardium. In turn, the myocardium is covered by two membranes, the pericardium, externally, and the endocardium that covers the inner wall.

The inside of the heart is divided into four chambers, the upper and the lower ones. The upper chambers are called atriums and are divided in left and right; the lower chambers are called ventricles. These chambers are made of the same kind of myocardium tissue. However, the walls of the ventricles are thicker and stronger compared with those of the atriums.

The left part and the right part are completely separate; every atrium, instead, communicates with the underlying ventricles through a heart valve that allows the flow of blood.

Between the atriums and the ventricles on the left is the bicuspid valve, while on the right there is the tricuspid valve. If one of the two heart valves is defective or is damaged a "heart murmur" occurs.

The heart completes two types of circulation: the heart-lung-heart circulation called the pulmonary circulation and the heart-rest-of-the-body circulation, the systemic circulation.

It is important to remember that the blood vessels are divided based on the direction of the blood flow: the veins are the vessels in which the blood drawn towards the heart flows, while the arteries are the vessels through which the blood moves away from the heart.

The blood flows into the heart through a large vessel, the inferior vena cava. The mechanism that keeps the circulation active is a rhythmic succession of contractions of the heart muscle to which the name heart cycle is given.

The heart has two main phases, diastole and systole.

During diastole the heart relaxes and the blood from the veins flows into the atriums and fills them completely.

During the phase called systole the heart contracts starting with a very short contraction of the atria that lasts about 0.1 seconds and fills the ventricles with blood completely. At the end of the atrium systole the ventricular systole begins and has a duration 0.3 seconds. The contraction of the ventricles closes the atrioventricular valves, opens the semilunar valves, pumps the blood into the pulmonary arteries and the aorta. At the end of the ventricular systole the atriums begin to relax and the blood coming from the veins begins to flow inside, giving way to a new heart cycle.