The circulatory systems was first discovered by Ibn Naf in 1242. He is considered the father of circulatory physiology and his findings were published in Commentary on Anatomy in Avicennu's Canon. Most Christian factions of the time, condemned the work because it was a theology. This caused his discovery to remain mostly unknown until the dissections of William Harvey (an English physician who was the first in the western world to correctly describe systemic circulation in detail) in 1616.
The circulatory system is also known as the cardiovascular system. It contains the heart and blood vessels that distribute blood and nutrients throughout the body. It consists of systemic and pulmonary circulation.
Pulmonary circulation is a closed circuit between the heart and lungs. It is the part of the cardiovascular system that carries deoxygenated blood away from the heart via the pulmonary arteries, the only arteries in the human body that carry deoxygenated blood. It then returns oxygenated blood back to the heart to be taken to the rest of the body.
The process begins when oxygen deselected blood leaves systemic (whole body) circulation when it enters the right atrium (upper heart chamber) through the inferior and superior vena cava. These are two veins which return blood from the body to the heart, the superior from the upper body and the inferior from the lower body.
Blood then travels through the tricuspid valve (aka right atrioventricular valve) into the right ventricle (lower heart chamber). From the right ventricle, blood is pumped through the pulmonary semilunar valve and into the pulmonary artery. This artery divides above the heart and branches into both the right and left lung.
These arteries further subdivide into smaller and smaller branches until capillaries in the pulmonary air sacs (alveoli) are reached. In the capillaries, blood takes up oxygen from the air breathed into the alveoli and carbon dioxide is released. This re oxygenated blood then flows into larger vessels until the pulmonary veins are reached. Pulmonary veins are the only veins in the human body that carry oxygenated blood.
The pulmonary veins open into the left atrium of the heart. Oxygenated blood then leaves through these veins and returns to the left atrium through the bicuspid valve also known as the mitral or the left atrioventricular valve, into the left ventricle. The valves the blood passes through in the veins are one way valves. This is important to prevent back flow of the blood. If the blood flows the wrong way, blood gases, oxygen and carbon dioxide, may mix causing a serious threat to the body. From the left ventricle, the blood is then distributed through the systemic circulation before returning once again to pulmonary circulation.
Pulmonary circulation is a closed system which carries blood from the heart to the lungs and back to the heart. It is a much needed part of the cardiovascular system. A complex system, in constant motion, providing a vital role in human existence.