Bone marrow is part of the immune system, which protects us from infection and disease. The marrow is in the spongy material found inside bones. This is where stem cells are made. Stem cells are blood cells at their earliest stage of development. All blood cells grow from stem cells. The bone marrow makes millions of blood cells every day. The three main types of blood cells are:
- red blood cells, which carry oxygen around the body
- white blood cells, which fight infections
- platelets, which help blood to clot to prevent bleeding.