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 closed circulatory systems, blood circulates in a continuous loop, ensuring that all cells receive the necessary substances for survival. Many animals, including humans, mammals, and birds, possess closed circulatory systems. This system contrasts with open circulatory systems, where blood flows freely through cavities. The closed system provides better control over blood flow and pressure, which is essential for maintaining homeostasis and supporting higher metabolic rates.