Many animals including all vertebrates, have a closed circulatory system in which the blood is enclosed within tubes.
This creates higher blood pressure as the blood flows along narrow channels. This means the blood travels faster and the blood system is more effiecient at moving substances around the body.
- The blood leaves the heart under pressure and flows along arteries and then arteioles (small arteries) to capillaries.
- There are a large amount of capillaries which come into close contact with most of the cells in the body, where substances are exchanges between blood and cells.
- After passing along the capillaries, the blood returns to the heart by means of venules ( small veins ) and then veins
- valves ensure that blood flows in only one direction.
Animals with closed systems and generally larger in size and more active.
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