This part of the circulatory system forms a second loop for the blood to travel through. It is not until it has made the trip to the lungs and back that blood is directed into the first loop that passes through the rest of the body. Therefore the lungs, heart, and blood vessels are often treated as a single system, of which the circulatory system is just a part. Although the primary function of the circulatory system is the transport of oxygen and carbon dioxide, much else is carried along with the blood - energy supplies for cells, water, hormones, minerals, immune system cells and substances, and other necessary materials. The materials include fats and cholesterol needed for building and maintaining cell membranes.
Blood flows from heart to lungs , where it exchanges carbon dioxide for oxygen.
The heart then pumps it through the body. Conditions that affect the circulatory system For the most part any condition or event that halts blood flow, completely or to a part of the body, results in death to the cells that are no longer receiving blood. If a vital organ is affected, the interference with blood flow can be fatal in a very short time. The most common way that blood flow is stopped is through buildup of material within an artery, as in atherosclerosis or embolism . A hole in the system allows blood to flow out of circulation.