foundation of the BLOODand its circulation and
plays a fundamental role in immune function. Red
bone marrow is the primary source of new blood
cells and is most abundant within the sternum,
ribs, vertebrae, and pelvis in an adult. In child-
hood the bones of the skull and face, and the long
bones of the arms and legs, also contain red bone
marrow. As the body matures the red bone mar-
row in these sites transitions to yellow bone mar-
row, which contains mostly connective tissue and
fat. The healthy adult has less than half as much
red bone marrow as blood.
About 99 percent of the red bone marrow’s
output is erythrocytes; erythropoiesis is the
process of producing erythrocytes. The red bone
marrow also produces platelets (clotting cells) and
granulocytes, a type of LEUKOCYTE (white blood
cell). The cells that make up the bone marrow are
BLOOD STEM CELLS, which continuously replicate to
replenish the bone marrow and differentiate into
three parent lines, or precursors, that produce
blood cells. The parent lines are
- erythroblasts, which produce erythrocytes
- megakaryoblasts, which produce platelets
- myeloblasts, which produce neutrophils,
basophils, and eosinophils (the three subtypes
of granulocytes)
The red bone marrow also warehouses plasma
cells, which are integral to immune function (not
related to the PLASMAthat forms the fluid base of
blood). The red bone marrow is the location
where B-cell lymphocytes, which migrate to the
marrow from the LY M P Htissues that produce them,
come to maturity. Yellow bone marrow produces a
few leukocytes in adulthood though primarily
functions as a reserve resource for new blood cell
production when the red bone marrow cannot
meet the body’s needs.
DISORDERS THAT AFFECT THE BONE MARROWANEMIA LEUKEMIA
LEUKOPENIA metastatic CANCER
MULTIPLE MYELOMA MYELODYSPLASIA SYNDROME
MYELOFIBROSIS NEUTROPENIA
POLYCYTHEMIA VERA radiation toxicity
THROMBOCYTHEMIA THROMBOCYTOPENIA
For further discussion of the bone marrow
within the context of blood and lymph structure
and function please see the overview section “The
Blood and Lymph.”
See alsoCELL STRUCTURE AND FUNCTION; ERYTHRO-
POIETIN(EPO); HEMATOPOIESIS; SPLEEN.bone marrow donation The withdrawal of BONE
MARROWfrom a donor for use as a BONE MARROW
TRANSPLANTATION or to harvest BLOOD STEM CELLS,
usually as treatments for LEUKEMIA, lymphoma,
some other cancers, and severe forms of ANEMIA.
BONE marrow donation may be autologous
(donated for reimplantation into the donor) or
allogeneic (donated for another person to receive
as a bone marrow transplantation).
Bone marrow donation is a surgical procedure
performed in an operating room under general
ANESTHESIA. The physician extracts donor bone
marrow, which is a thick liquid, using a syringe
and a large needle that can pierce the bone. The
most common donor site is the iliac crest (hip
bone). A single bone marrow donation typically
harvests about 1 quart (less than a liter) of red
bone marrow mixed with BLOOD. The donor’s body
replaces the extracted marrow in about four to six
weeks. The risks of bone marrow donation are
slight. They include postoperative bleeding and
INFECTION. The withdrawal site is typically uncom-
fortable for a few days after the donation.
There is no cost to the donor for the bone mar-
row donation procedure and care related to it
unless the donor is also to be the recipient (autol-
ogous donation). Prospective donors register with
a bone marrow donor program, which uses blood
samples to identify tissue types. The program con-
tacts the prospective donor when there is a need
for marrow of his or her tissue type. Unlike blood
donated for transfusions, bone marrow cannot be
stored.
A less invasive type of donation that appears to
achieve the same result is peripheral blood stem
cell (PBSC) collection, done through a procedure
called HEMAPHERESIS(also called apheresis). Hema-
pheresis is similar to BLOOD DONATION, in which an
intravenous (IV) line withdraws the donor’s
blood. The blood goes into a blood separator that
extracts the blood stem cells and returns the
remainder of the blood to the donor via a second132 The Blood and Lymph