After leaving the heart, the oxygenated blood flows into the body's largest artery, the aorta. All the arteries of the systemic circulation branch from the aorta to carry the oxygenated blood to the cells of the body's tissues. The arteries branch numerous times, eventually, branching into the small arterioles which connect to the capillary beds found in within all tissue. In the capillary beds of the systemic circulation not only are oxygen, nutrients, and hormones delivered to cells and wastes collected from cells, but, also, nutrients are picked up in capillary beds found in the intestine and liver, wastes discharged in capillary beds in the kidneys, and hormones picked up in capillary beds in the endocrine glands. Substances such as nutrients and hormones acquired by the blood in the systemic circulation will be delivered to all cells after traveling back to the heart, then, through the pulmonary circulation, and, finally, back through the arteries and capillaries of the systemic circulation. From the capillaries, blood in the systemic circulation begins its return to the heart through the small venules, then, through the larger veins, and, finally, through the two largest veins, the anterior vena cava, which drains the head, neck, and arms, and the posterior vena cava, which drains the rest of the body. These two veins empty into the right atrium of the heart.
