A type of circulatory system where blood circulates within closed vessels, thus, blood is distinct from the interstitial fluid
The circulatory system is one of the transport systems through which nutrients, gases, and other molecules are transported within the body of animals. There are two major types of circulatory systems: the open circulatory system and the closed circulatory system. In open circulatory system, the blood bathes the cells directly as opposed in closed circulatory system wherein the blood travels through vessels. Since the blood in an open circulatory system is not confined to vessels the blood and the interstitial fluid have no distinction. In contrast, the blood and the interstitial fluid do not mix in a closed circulatory system. A closed circulatory system is comprised of the heart that pumps blood into the vessels to reach the tissues and organs. The exchange of gases in the bloodstream occurs between smaller vessels (capillaries) and tissues.
Examples of animals with a closed circulatory system are annelids and vertebrates (including humans). Humans have a cardiovascular system comprised of heart and blood vessels that circulate blood throughout the body and another system for circulating lymph called lymphatic system.