Thursday, June 23, 2011

Bone Marrow Transplant: What, Why, and How | Healthmad

A complete primer on bone marrow transplant.

What is Bone Marrow

Bones are not solid, but instead are made up both compact and spongy structure. The compact bone gives strength, while the spongy bone contains the marrow.

The outer, weight-bearing area is hard, compact, and calcium-based. The inner region is a lattice-work of fibrous bone known as cancellous tissue.
Bone marrow is a soft fatty tissue that fills the cavities of certain bones – such as the sternum (middle of the chest), pelvis (hip bone), and femur (thigh bone). It fills the shafts of the long bones, the trabeculae (spaces within cancellous tissue), and extends into the bony canals that hold the blood vessels.
Our skull, sternum, ribs, pelvis, and femur bones all contain bone marrow, but other smaller bones do not contain the marrow. Inside this special tissue, stems cells reside. Stem cells are large “primitive” undifferentiated cells.

While they are undifferentiated, the stem cells wait until unhealthy, weakened, or damaged cells need to be replaced. These stem cells transform themselves into white and red blood cells and platelets, essential for immunity and circulation. This process is directed by subtle chemical cues that vary according to location and conditions in the body.
Any of the blood cells that comprise the bloodstream within the arteries and veins are born from stem cells and mature within the bone marrow.
Importance of Bone Marrow

Stem cells within the bone marrow continuously divide to form new cells. Some of the new cells remain unchanged as stem cells and have a lifelong capacity for self-renewal. These cells are called pluripotent cells. These are capable of transforming themselves into all the tissues that compose a living being, except the extra-embryonic membranes (placenta).
Bone marrow is a critical part of the body because it is the body’s main blood cell “factory.”
Other, unipotent stem cells have a limited capacity for self-renewal.These cells become committed to forming only one type of blood cell line—erythrocytes (red blood cells which carry oxygen around the body), leukocytes (white blood cells which help fight infection), or platelets which help stop bleeding.
Thus, we see that the marrow is the principal site for blood formation (hematopoiesis), which occurs primarily in the bones of the legs, arms, ribs, breastbone (sternum), and spine (vertebrae).

Sources of Bone Marrow Stem Cells

  • Bone marrow harvest: Stem cells are harvested for future use by taking them directly out of the bone. Under anesthesia, a needle is inserted into either the hip or the breastbone to take out some bone marrow.
  • Apheresis: A more common method is to collect stem cells from a donor blood and pass it through an apparatus that separate out one particular constituent and return the remainder to the circulation. To get the stem cell out of the marrow into the blood stream, the donor is given injections for a few days. Then the donor is connected to a machine by a needle inserted in the vein and the blood is taken from the vein. It is then filtered by the machine to collect the stem cells, then the residual blood returned back to the donor through a needle in the other arm.
  • Umbilical cord blood: Stem cells are taken from an umbilical cord right after delivery of an infant. The stem cells are tested, typed, counted, and frozen until they are needed for a transplant. Umbilical cord blood requires less stringent matching because the stems cells are so immature. These cord blood stem cells are important because they do not need to be as closely matched as bone marrow or peripheral blood stem cells to ensure a successful outcome.

What is bone Marrow Transplant

Bone marrow transplantation (also known as stem cell transplantation) involves harvesting healthy stem cells to replenish the bone marrow of the patient. The new stem cells take over the production of the blood cells.

A bone marrow transplant delivers healthy bone marrow stem cells into the patient. Stem cells that are normally found in the bone marrow are taken out, filtered, and given back either to the same person or to another person. It replaces bone marrow that is either not working properly or has been ablated—destroyed—by chemotherapy or radiation.

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