A closed circulatory system is a type of circulatory system where blood is contained within vessels, such as arteries and veins. This system allows for efficient transport of nutrients, gases, and waste products throughout the body. In organisms with a closed circulatory system, blood circulates in a continuous loop, ensuring that oxygen-rich blood reaches tissues while carbon dioxide is removed. Many animals, including humans, mammals, and birds, possess a closed circulatory system. This system contrasts with an open circulatory system, where blood flows freely through cavities. The closed system provides better control over blood flow and pressure, supporting higher metabolic rates and more complex body structures.