The basic function of a transport is to bring about rapid made flow of materials, such as soluble food, excretory products and oxygen, throughout the body. At appropriate sites, these materials must be able to leave the transport system and enter the cells and tissues that either use them or excrete them. At the same time, materials from various cells tissues must be able yo enter the transport system to be carried to their destination. In most animals, such a transport system, also called a circulatory system, usually has these features:
• A circulating fluid, which is usually blood;
• A pumping device or heart to drive the fluid around the body;
• A system of branched tubes or vessels connected to the heart, through which the fluid can circulate.
In animals, there are two types of circulatory system: the open and the closed circulatory systems.
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