What type of circulatory system is characterized by a heart and blood vessels?

A closed circulatory system is characterized by the presence of a heart and a network of blood vessels that confine the blood within these vessels, allowing for efficient distribution of nutrients and oxygen throughout the body. In this system, the blood circulates in a closed loop and does not mix with the interstitial fluid surrounding the tissues. This separation enables more effective regulation of blood pressure and flow, which supports the metabolic demands of larger and more active organisms, such as mammals and birds.

In contrast, an open circulatory system, which is seen in many invertebrates, does not have blood confined exclusively to vessels; instead, it bathes the organs directly in hemolymph, lacking a centralized pumping mechanism comparable to a heart. The single and double circulatory system terms refer to different structural configurations within closed systems: a single circulatory system is found in organisms like fish, where blood flows in one loop, while a double circulatory system, seen in mammals, involves two loops (pulmonary and systemic) for more efficient oxygenation and nutrient delivery. However, the core characteristic of the presence of a heart and blood vessels specifically defines a closed circulatory system.