circulatory system

The function of circulatory system : transport of respiratory gases, hormone distrubition, heat distrubution, immune defence. Circulatory system has three essential components; a circulating fluid, a vascular system and heart. Lower metazoans lack a body cavity and do not have an internal circulatory system. Coelentrate do not have also an internal circulatory system because their body wall is very thin.

The body cavity of higher pseudocoelomate and coelomate animals contains a coelomic fluid. Some of the coelomate animalssuch as crustaceans, the vascular system is mesodermal tube that partially seperates thee blood from hemocoel.

A heart may be present to propel hemolymph through the vessels. In other some coelomate animals, the ceolom completely seperated from coelom. The closed circulatory system have a complete system of vessels and the blood is completely seperate and has a ddifferent composition from the interstitial fluid.