446 The circulatory system consists of two loops. The shorter loop, called pulmonary circulation, begins at the right side of the heart and delivers blood to the lungs before returning the oxygenated blood to the left side of the heart. The longer loop, comprising systemic circulation, begins at the left side of the heart and pumps blood through arteries to tissues of the body, and then returns blood through veins to the right side of the heart.
