The systemic circle goes from the left ventricle to the right atrium.
From the left ventricle originates the aorta, which branches into smaller vessels gradually going to vascularize the various organs and tissues. Then from the left ventricle the oxygenated blood reaches the rest of the body. Through the capillaries oxygen (O 2 ) is transferred to the tissues and carbon dioxide (CO 2 ) is detected, so that the arterial blood becomes venous.
Venous blood from the capillaries passes into venous vessels of a caliber gradually increasing and finally returns to the right atrium through the two major venous vessels, namely the superior vena cava and the inferior vena cava, the first which drains the blood belonging to the sopraniaframatic region and the second that drains the blood from the sub-diaphragmatic region.