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Systemic Circulation: Serves all tissues and organs (excluding the lungs), delivering oxygen-rich blood and collecting deoxygenated blood. These tissues uptake oxygen and release carbon dioxide into the blood.
Pulmonary Circulation: Moves blood between the heart and the lungs, where gas exchange occurs—oxygen is absorbed, and carbon dioxide is expelled.
In mammals and birds, these systems are connected in a series, meaning blood flows sequentially through the lungs, heart, and body tissues. This setup ensures a continuous, unidirectional flow, efficiently oxygenating blood before distribution.
The Role of Blood and Hemolymph
Blood transports oxygen, carbon dioxide, nutrients, hormones, immune agents, heat, and waste.