Explain the working of Pulmonary Circulation?

In pulmonary circulation, blood is pumped to the lungs, where carbon dioxide is exchanged for oxygen. Blood returning from the body, containing a high concentration of CO₂ and a low concentration of O₂, enters the right atrium, and is pumped through the tricuspid valve into the right ventricle. The right ventricle pumps blood through the pulmonary valve into the pulmonary artery, which divides into two smaller arteries, one leading to each lung. These arteries subsequently divide into smaller branched arterioles, and then into fine capillaries.

The capillaries surrounding the alveoli making up the lungs are small and very thin-walled. Only one red blood cell is able to pass through at a time. Oxygen diffuses from the alveoli through the capillary walls and into the blood stream, where it combines with hemoglobin molecules in red blood cells. Carbon dioxide diffuses in the opposite direction, from the hemoglobin in red blood cells, through the capillary walls, and into the alveoli, where it is exhaled to the atmosphere.

Upon becoming oxygenated, blood returns from the lungs through venules that join to form four pulmonary veins leading to the left atrium of the heart. The left atrium will then pump the blood through the bicuspid valve into the left ventricle.

Note that the pulmonary arteries are the only arteries that carry deoxygenated blood and the pulmonary veins are the only veins that carry oxygenated blood. The assimilation of oxygen is accompanied by a change in color of blood from a dark to a bright red. In most cases, one is usually able to distinguish between arterial blood and venous blood by its color.