Pulmonary Circulation

Pulmonary circulation is one part of the cardiovascular system that serves the lungs exclusively. Its role is to transport oxygen depleted blood away from the heart to the lungs, and return back to the heart with oxygen rich blood.

Physicians and scientists have been examining the role of the heart and blood for thousands of years. One of the earliest writings known on the circulatory system can be found in the Ebers Papyrus, an ancient Egyptian medical papyrus that contains over seven hundred remedies and prescriptions, both physical and spiritual. The Egyptians thought that when a person breathed in air through the mouth, it would then travel to the lungs and the heart. From the heart the air would travel to all parts of the body through the arteries. Despite the fact that this concept has since been proved to be flawed, one can only appreciate that it reflects great scientific thought in ancient times.

In the year1242, an Arabian physician by the name of Ibn al-Nafis is noted to be the first person to describe the process on how blood traveled throughout the body, with a special emphasis on pulmonary circulation. He is credited with being the father of circulatory physiology. Hieronymus Fabricus, a professor at the University of Padua, Italy, later discovered that the veins in the body had valves within them; however he was unable to determine what their function was.

It was actually William Harvey, (who studied under Fabricus while at Padua), in 1628 that announced his discovery of the human circulatory system in his book titled, Exercitatio Anatomica de Motu Cordis et Sanguinis in Animalibus (An Anatomical Exercise of the Motion of the Heart and Blood in Animals). It was his research and dedicated work that convinced the medical world in regards to the many functions of the circulatory system.

Through the efforts of these men and those who followed we now have a greater understanding of how blood flows through the body and the unique functions of all the systems along the way.

In regards to pulmonary circulation, we now know that this is just one phase of the overall circulatory system. The valves that Fabricus spoke of have now been shown to have a great purpose. The valves within the veins are one-way valves and play a vital role in preventing any backward flow of blood. The circulatory system is in essence a complex network of one-way streets. Should blood begin flowing in the wrong direction, the gases within the blood (oxygen and carbon dioxide) could potentially mix, causing serious harm to the body. The following is a description of the one-way path that the blood travels in relation to pulmonary circulation.

The veins carry oxygen depleted, waste-rich blood to the heart, where it enters the right atrium via two large veins called the Inferior Vena Cavae and the Superior Vena Cavae. The blood is then pumped through a one-way valve (the tricuspid valve) into the right ventricle. The right ventricle fills with blood, then contracts, pumping the blood through the pulmonary semilunar valve, pushing it into two pulmonary arteries, one for each lung.

While in the lungs, and within the capillaries, the red blood cells release carbon dioxide and pick up oxygen during respiration. This freshly oxygenated blood then leaves the lungs by way of the pulmonary veins and returns to the left side of the heart, entering into the left atrium. The blood then passes through another one-way valve called the biscuspid valve (also known as the mitral valve) into the left ventricle. The left ventricle fills with blood, then contracts, forcing the blood into the bodies main artery called the aorta, where it then travels throughout the body. This process is then continually repeated throughout a persons lifespan, amazingly without a person even having to think about it.