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what is circulation
what are blood vessels
what are arteries
what are capillaries
what do the walls of arteries need to be
how much blood vessels in a child
how much blood vessels in an adult
how thick are capillaries
what do capillaries form
capillaries are a network of what
what are veins
what are bruises
what si the size of your heart
what muscle is the heart made of
why is the circularity system a double system
what is blood rich in oxygen called
what is blood with carbon dioxide called
how many chambers does the heart have
what are the 3 phases of heartbeat
what are the 2 blood cells
