systemic circulation

systemic circulation, in physiology, the portion of the circulatory system that carries oxygen- and nutrient-rich blood from the heart to the tissues of the body and returns oxygen-depleted blood back to the heart. Together with pulmonary circulation, which carries blood between the heart and lungs, it forms one of the two major components of the cardiovascular system.

Pressure generated by the pumping action of the heart provides the force that drives systemic blood flow. Thus, systemic circulation begins when the left ventricle pumps oxygenated blood into the aorta, the body’s largest artery. From there, blood travels through a branching network of arteries and smaller arterioles before reaching the capillaries, where oxygen, nutrients, hormones, and other substances are exchanged with surrounding tissues. Carbon dioxide and metabolic waste products enter the bloodstream at the capillary level. The blood then flows into venules and veins and ultimately returns to the heart through the superior and inferior venae cavae, which empty into the right atrium.

Although the systemic circulation functions as a single network, it is composed of numerous parallel pathways serving different organs and tissues. Blood flow through these pathways can be adjusted independently according to the body’s needs. For example, circulation to the digestive system increases after a meal to support nutrient absorption, whereas blood flow to skeletal muscles rises during exercise. This regulation occurs primarily through changes in the diameter of arterioles, which alter vascular resistance and help direct blood to the tissues that require it most.

By continuously transporting oxygen, nutrients, immune cells, hormones, and waste products throughout the body, systemic circulation plays a central role in maintaining homeostasis and supporting the function of virtually every organ system. Disorders that disupt this essential system include hypertension, atherosclerosis, heart failure, and shock, which can impair tissue perfusion and compromise organ function.