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