Final answer:
The spleen receives blood from the systemic circuit, which distributes oxygenated blood to all body tissues.
Step-by-step explanation:
The circuit that delivers blood to the spleen is the systemic circuit. The pulmonary circuit is responsible for transporting blood to and from the lungs to pick up oxygen and expel carbon dioxide. Once the blood is oxygenated in the lungs, it re-enters the heart and is pumped out through the systemic arteries such as the aorta. These arteries then distribute blood to various organs of the body, including the spleen. The systemic circuit is crucial because it transports oxygenated blood from the left side of the heart to all body tissues and returns deoxygenated blood to the right side of the heart.