In a healthy person, blood circulation takes place with two main circulatory systems, small and large blood circulation. With the small (pulmonary) blood circulation, oxygen-poor blood collected from the body is sent from the heart to the lungs, while with the large circulation, oxygen-rich blood is sent from the lungs to the whole body.
Blood is transported throughout the body through veins. Various factors can cause blood to clot in the vein. The resulting clot is transported to different tissues or organs in the body, causing vascular occlusion. This condition is called embolism.
The formation of a blood clot in one of the arteries carrying blood from the heart to the lungs and the sudden blockage of the vessel is called a pulmonary (lung) embolism. A clot in the veins that reaches the lungs can prevent the passage of blood to the lungs, causing deoxygenated blood circulation in the body. Being without oxygen for a long time can disrupt the functioning of many organs such as the brain, kidney, heart, stomach.