In which circulatory system is blood pumped into cavities instead of being confined to blood vessels?

The open circulatory system is characterized by the way blood circulates throughout the body. In this system, blood is not contained solely within blood vessels but is pumped into open spaces or cavities, known as hemocoel. This allows the blood, or hemolymph as it is often referred, to directly bathe the organs and tissues, facilitating the exchange of gases and nutrients.

In organisms with an open circulatory system, such as many invertebrates like insects and crustaceans, the heart pumps the hemolymph into these body cavities. Since the blood directly interacts with the tissues, the system tends to be less efficient for oxygen and nutrient transport compared to closed systems where blood flows through a network of vessels, allowing for more controlled and directed circulation.

In contrast, the closed circulatory system keeps the blood confined within vessels, allowing for more efficient transport of substances and better regulation of blood flow. The lymphatic system is concerned with the transport of lymph, rather than blood, and systemic circulation refers to the pathways blood takes from the heart to the body and back. Hence, the unique feature of blood being pumped into cavities distinctly identifies the open circulatory system.