To understand ET, it helps to know a little about the bone marrow. 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 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.
The bone marrow makes millions of blood cells every day. When the cells are mature they are released into the blood stream. In myeloproliferative neoplasms (MPNs), bone marrow makes too many of one or more types of blood cells.