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Filling up the petrol tank of a motor car is of no use, unless there is a pipeline to convey the petrol from the tank into the engine.
Similarly it is an essential requirement of most animals to transport the materials from the parts of the body where they are formed or taken up to others.
Where they are needed or got rid of this function is performed by fluid that circulates throughout the body in a regular way.
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Similarly human body possess in extensive pipeline system called circulatory system (Fig. 1.1). For transporting materials between various body parts, as well as for gaseous exchange from the external environment.
This circulatory system includes, heart, blood vessels and blood. Circulatory system is also called as cardiovascular system.
Types of Circulatory Systems:
There are two types of circulatory Systems.
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1. Open circulatory System:
It is called open system because the blood vessels open into spaces and not into capillaries. The main blood vessels arising from the heart, pour the blood into tissue spaces called sinuses. This is common in prawns, crabs, spiders and insects.
2. Closed circulatory system:
It is common in Annelids, Invertebrates and all vertebrates including human beings. In this type of circulatory system, blood remains in blood vessels and never coming in direct contact with tissue cells. The strong pumping action of heart makes the blood flow rapidly and with pressure in the arteries.
Importance of the Circulating System:
1. It carries food substances to the all body cells.
2. Carries absorbed oxygen to each cell of the body.
3. Caring back carbon dioxide to the lungs.
4. Helping in removal of harmful chemical substance from the body.
