How do the pulmonary and systemic circuits differ?

The pulmonary and systemic circuits serve distinct roles in the circulatory system, and the correct option highlights a key aspect of the pulmonary circuit's function.

The pulmonary circuit is responsible for transporting deoxygenated blood from the heart to the lungs. In the lungs, this blood releases carbon dioxide and picks up oxygen, thus oxygenating the blood before it returns to the heart and enters the systemic circuit. This process is essential for ensuring that oxygen is delivered to the body's tissues and organs for cellular respiration.

In contrast, the systemic circuit carries oxygenated blood away from the heart to the rest of the body and returns deoxygenated blood back to the heart. Therefore, while the systemic circuit is primarily concerned with delivering oxygen to the tissues, the pulmonary circuit specifically focuses on the exchange of gases in the lungs, underscoring why it transporting deoxygenated blood to the lungs is a defining characteristic.