The circulatory system is a vast network of organs and vessels that is responsible for the flow of blood, nutrients, oxygen and other gases, and hormones to and from cells. The system consists of three independent systems that work together: the heart (cardiovascular), lungs (pulmonary), and arteries, veins, coronary and portal vessels (systemic). Together, the heart, blood, and blood vessels make up the cardiovascular component of the circulatory system. It includes the pulmonary circulation, a "loop" through the lungs where blood is oxygenated. It also incorporates the systemic circulation, which runs through the rest of the body to provide oxygenated blood. 
Because of its vastness and critical nature, the circulatory system is one of the systems of the body most prone to disease. Disorders of this system are the leading cause of death among adults in the majority of countries world-wide, arteriosclerosis being one of  the most common diseases. It is characterized by  fatty deposits in the arteries that cause the walls to stiffen and thicken the walls, and may result in restricted blood flow and ischemia. This may result in symptoms such as angina and dyspnea, necrosis, and ultimately in heart attack or stroke. Hypertension, another circulatory is disease, causes the heart to work harder and can lead to complications as a heart attack, a stroke, or kidney failure. Abnormal blood lipid levels, that is high total cholesterol, high levels of triglycerides, high levels of low-density lipoprotein or low levels of high-density lipoprotein (HDL) cholesterol all increase the risk of heart disease and stroke, and are of particular interest of modern research. Besides changing food intake habits of patients suffering from cardiovascular diseases, in combination with the stimulation to increase physical exercise, special medication may also modify a patients blood lipid profile and prevent the person from developing life threatening circulatory diseases.