Blood cells form in the bone marrow. Bone marrow is the soft material in the center of most bones.

Immature blood cells are called stem cells and blasts. Most blood cells mature in the bone marrow and then move into the blood vessels. Blood flowing through the blood vessels and heart is called the peripheral blood.

The bone marrow makes different types of blood cells. Each type has a special function:

	White blood cells help fight infection.
	Red blood cells carry oxygen to tissues throughout the body.
	Platelets help form blood clots that control bleeding.

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