The cardiovascular system is a closed system if the heart and blood vessels. The heart pumps blood through a closed system of blood vessels. Blood vessels allow blood to circulate to all parts of the body. Arteries usually colored red because oxygen rich, carry blood away from the heart to capillaries within the tissues. Veins usually colored blue because oxygen poor, carry blood to the heart from the capillaries. Capillaries are the smallest vessels within the tissues where gas exchange take place. The function of the cardiovascular system is to deliver oxygen and nutrients to the body tissues and remove carbon dioxide and wastes products. The vital importance of the heart is obvious. If one assumes an average rate of contraction of 75 contractions per minute, a human heart would contract approximately 108,000 times in one day, more than 39 million times in one year, and nearly 3 billion times during a 75-year lifespan. Each of the major pumping chambers of the heart ejects approximately 70 mL blood per contraction in a resting adult.
