A circulatory system is a network that transports blood, nutrients, gases, and waste products throughout an organism's body. In humans and many animals, this system consists of the heart, blood vessels, and blood. The heart pumps blood through arteries, veins, and capillaries, ensuring that oxygen and nutrients reach cells while removing carbon dioxide and other waste. There are two main types of circulatory systems: open circulatory systems and closed circulatory systems. In an open system, blood flows freely through cavities, while in a closed system, blood is contained within vessels. Most vertebrates, including humans, have a closed circulatory system, which allows for more efficient transport.