The Bone Marrow
The bone marrow is a soft tissue found inside the bones in the body; mainly the iliac crests (or the hip bone), the breast bone and the skull. Colloquially it can be called the marrow.
Often it is confused with the spinal cord. However, they bear absolutely no relation. The function of both parts is completely different. The spinal cord is found in the spinal column and its function is to transmit nerve impulses from the brain to parts of the body and vice versa.
The bone marrow contains cells that have not matured called the hematopoietic stem cells. It is these stem cells that make up the cells that are contained in the blood. The division of the stem cells leads to the creation of all the cell types contained in the blood. There are three different classes of blood cell: the white blood cells defend the body against infections; the red blood cells transport oxygen around the body; and the platelets help to colt the blood.
Illustration by Carmen Bueno
The bone marrow can be transplanted by extracting a sample from the bone of a living donor. The sample is normally taken from the hip bone, through a process of puncture, extraction, and transfusion into the circulatory system of the recipient. This process requires compatibility between the HLA system of the donor and the recipient. The transfused stem cells will be added to the bone marrow of the bones in the recipient. This process is known as the bone marrow transplant.
With the aim of minimizing any possible secondary effects for the patient, the doctors attempt to find the best possible stem cell match for the transplant. Each person has a distinct set of proteins called the HLA (Human Leukocyte Antigens system), located in the surface of the cells. This collection of HLA proteins are identified through a special blood test.
The greater the number of compatible HLA antigens, the greater the possibility that the patient will accept the donated cells.
There is a stronger possibility that patients will be compatible with their close relations (especially with their siblings) than with unrelated people. However, only 1 in every 4 patients has a compatible family member. The rest have to resort to a Bone Marrow Donor Registry, which in Spain is known as the REDMO and is administered by the José Carreras Foundation.
Microscopic image of the bone marrow in a healthy person
Microscopic image of the bone marrow of an Acute Lymphoblastic Leukaemia patient