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| Types of Circulatory System |
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| Animals possess two type of circulatory system. They are |
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| a) Open type and |
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| b) Closed type |
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| In this type of circulatory system the blood may be present in the blood vessels for some time but finally it comes out of the blood vessels. The internal organs are directly bathed in blood. The blood flows from the heart into the arteries. The artery open into large spaces called sinuses. From the sinus the blood is carried by the veins to the heart. There are no inter connecting vessels or capillaries between the arteries and the veins, as the blood comes out of blood vessels. This type of circulatory system is called open type. It occurs in annelids like leeches, arthropods, most of the molluscs and ascidians. |
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| In the closed type of circulatory system, the blood remains inside the blood vessels and does not come out. The blood flows from arteries to veins through small blood vessels called capillaries. The closed type of circulatory system occurs in most of the Annelids, Cephalopods and Vertebrates including man. |
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| 1) The blood flows at a very low velocity and at low pressure due to the absence of smooth muscles. |
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| 2) There is direct exchange of materials between the cells and the blood because of the direct contact between them. |
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| 3) The respiratory pigment, when present, is dissolved in the plasma of the blood and there are no red corpuscles. |
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| 1) The speed of circulation is more rapid due to the presence of muscular and contractile blood vessels. |
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| 2) The supply and removal of materials to and from the tissues by the blood is enhanced, thereby increasing the efficiency of circulation. |
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| 3) The volume of blood flowing through a tissue or organ is regulated by the contraction and relaxation of the muscles of the blood vessels. |
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