Bone marrow is the soft, spongy tissue found in the inner part of bones made up of blood-forming cells, fat cells, and tissues that help the growth of blood cells. All types of blood cells are produced in the bone marrow from an early cell called stem cell. These stem cells grow in an orderly fashion to produce red blood cells (erythrocytes), white blood cells (leukocytes), and platelets (thrombocytes).
The red blood cells carry oxygen from the lungs to all tissues of the body and remove carbon dioxide, a metabolic waste product. A decrease in red blood cells (anaemia) causes weakness, shortness of breath, and tiredness. White blood cells help the body to fight against germs - viruses and bacteria. They are of several types – those with granules (granulocytes), which comprise neutrophils, eosinophils and basophils, and those with a single nucleus (mononuclear cells), the lymphocytes and monocytes. Each of these has a special role to play in protecting the body against infection. Their lack (leukopaenia) predisposes to infections. Platelets are fragments of a marrow cell, called megakaryocyte, and are so called because they look a little bit like plates when seen under the microscope. Platelets are responsible for clotting of blood and help stop bleeding. A decrease in platelets (thrombocytopaenia) may lead to bleeding problems.
When a person's bone marrow has been damaged or destroyed due to a disease or intense treatment (radiation or chemotherapy for cancer), it leads to marrow failure i.e. the inability to produce normal blood cells. This may involve either one cell line or all of the cell lines. Bone marrow failure may be inherited or acquired and the underlying defect may be:
a) A decrease in or damage to the stem cells affecting them quantitatively or qualitatively (hypoplastic or aplastic anaemia)
b) Maturation defects (as may be seen on deficiency of vitamin B12 or folate)
c) Defects in differentiation (myelodysplastic syndromes). Immune mechanisms and genetic mutations may also lead to this.
The severity and extent of anaemia, leukopaenia &/or thrombocytopaenia determine the prognosis and treatment.