When the right ventricle contracts the blood is pumped into both lungs via the pulmonary artery. This portion of the circulatory system is sometimes referred to as pulmonary circulation or lesser circulation. The pulmonary artery is the only artery in the body that carries de-oxygenated blood. Blood is returned from the lungs via the pulmonary veins. These are the only veins in the body that carry oxygenated blood. The oxygenated blood is returned to the left atrium. When the atrium contracts the blood is forced into the left ventricle. The left ventricle is the strongest and most muscular portion of a healthy heart. This is due to the fact that the left ventricle works the hardest. It must force blood throughout the body. When the left ventricle contracts, blood is forced into the aorta. The aorta is the main artery leaving the heart.
The oxygenated blood is now forced throughout the body through a series of arteries that gradually become smaller and smaller. Blood flows from arteries into arterioles. From arterioles into capillaries. At this point the blood is able to make close contact with individual cells. Here is were waste products are picked up and oxygen is delivered.
The blood now starts its return trip to the heart. From the capillaries the blood flows into venules. These are very small veins. (About the same size as capillaries) From the venules the blood is forced into veins These veins all return blood either into the superior or the inferior vena cava. As stated earlier, the inferior and the superior vena cava return the de-oxygenated blood to the right atrium of the heart.
Please watch the fallowing video to improve your visual knowledge about the circulatory system: