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There are two types of blood circulatory systems:
- Open circulatory system
- Closed circulatory system
The blood enters and circulates in the interstitial spaces (space between the tissues).
The exchange of materials between the cells and the blood is done directly. There are few blood vessels but they are not extensive. The blood vessels are open-ended as they open into the common cavities called the haemocoel. For example: Insects
The blood always remains inside the blood vessels and never comes in direct contact with the cells. The materials enter and exit the blood vessels through the walls. The blood flows in the blood vessels under high pressure such that it reaches all the parts of the body in good time. The blood vessels are branched into fine capillaries which are actually involved in the exchange of materials. For example: Mammals (including man)
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