Final answer:
The pulmonary and systemic circuits are the two linked circuits in human circulation, responsible for gas exchange in the lungs and nutrient delivery to body tissues, respectively.
Step-by-step explanation:
The two distinct but linked circuits in the human circulation are called the pulmonary and systemic circuits. The pulmonary circuit is responsible for transporting blood to the lungs to pick up oxygen and to expel carbon dioxide, while the systemic circuit distributes the oxygenated blood to all other parts of the body and returns deoxygenated blood back to the heart.
The blood circulation in the body follows this dual-pathway approach to ensure efficient gas exchange and nutrient delivery to tissues. It takes about 20 seconds for blood to complete a cycle through both circulations, signifying the circulatory system's rapid response to the body's needs.