Bone marrow is the soft spongy tissue inside the bones that give rise to stem cells. Stem cells consist of cells that have not differentiated into a "type." As these stem cells mature, they differentiate according to their intended function and turn into either red blood cells, white blood cells or platelets. Following maturation, the cells are released from the bone marrow into the bloodstream. According to the American Association for Clinical Chemistry (AACC), bone marrow diseases occur due to a variety of causes including an abnormality in the production of blood cells or defects to the precursor stem cells.
Leukemia
Malignant cancer affecting the white blood cells group under the term leukemia. In this condition, abnormal leukemic cells continuously multiply by replication, then mature and suppress other normal cells by simply crowding them out. According to "Pathophysiology made Incredibly Easy" by Lippincott Williams & Wilkins, leukemia is classified as acute or chronic, and either lymphocytic or myeloid. Acute lymphocytic leukemia primarily affects children, while acute myeloid leukemia affects mostly adults. According to the AACC, people with leukemia experience frequent infections due to lack of normal white blood cells, fatigue and anemia due to reduced red blood cells and easily bleed or bruise due to decreased platelets. Other symptoms include bone pain and night sweats, as well as enlarged spleen, liver and lymph nodes over the course of the disease.
Aplastic Anemia
According to the National Hematologic Diseases Information Service, aplastic anemia affects all three types of blood cells by hindering or completely stopping their production. Commonly, red blood cells are most affected by the disease. With aplastic anemia, the stem cells that give rise to the different blood cells are damaged and do not replicate normally, therefore the bone marrow produces very limited amounts of healthy functioning cells. Causes of this disease include exposure to certain chemicals or radiation, drugs, viral infections or inheritance.
Myeloproliferative Disorders (MPDs)
The bone marrow works by a "supply and demand" system of producing mature blood cells. When there is a shortage of a type of cell due to aging, dying or removal from the circulation, precursor stem cells in the marrow differentiate and produce that blood cell for replacement. With myeloproliferative disorders, the system goes awry and overproduction of a single cell type results in suppression and crowding-out of the other blood cells leading to a systemic dysfunction. Also according to the AACC, four conditions fall under MPDs: chronic myelogenous leukemia, polycythemia vera, agnogenic myeloid metaplasia and essential thrombocytopenia.
Myelodysplastic Syndrome (MDS)
Similar to aplastic anemia, MDS conditions are characterized by an underproduction of blood cells. However, in contrast to aplastic anemia, the result is not a shortage of healthy blood cells but rather defective stem cells that have not matured normally. The matured cells often die off within the bone marrow. In the case that they do enter the circulation, the cells do not function properly and do not survive for long. The National Hematologic Diseases Information Service also states mostly older adults develop MDS and some forms of MDS frequently progress to leukemia.
References
- American Association for Clinical Chemistry: Bone Marrow Disorders
- "Pathophysiology made Incredibly Easy"; Lippincott Williams & Wilkins; 2009
- National Hematologic Diseases Information Service: Aplastic Anemia and Myelodysplastic Syndromes
- American Association of Clinical Chemistry: Myeloproliferative Disorders
