Synonyms
Medulla ossium
Definition
The bone marrow fills the interior of the bone and is the main site of blood formation in humans. Many diseases are caused by an imbalance in cell formation in the bone marrow. For example, leukemias and anemias (anemia), which can occur in the context of many basic diseases.
Anatomy
The bone marrow is located in the innermost part of human bones and accounts for about 2500 grams of body weight. It is divided into yellow and red bone marrow. The red bone marrow is the site of blood formation, whereas the yellow one is not, it is called fat marrow.
In newborns, the red bone marrow makes up the main part, but in the course of development it changes to yellow as much as possible, so that in an adult, red – blood-forming – bone marrow is only found in certain bones. These include the bones of the trunk, such as rib bones, sternum, vertebral bones, pelvic bones and clavicles, as well as skull bones and the ends (epiphyses) of the long tubular bones of arm and leg. Before birth, other organs besides the bone marrow play an important role in blood formation.
Thus, the main places of blood formation between the 2nd and 7th month of the fetus are mainly the liver and the spleen. The bone marrow has another important function besides blood formation. It is a part of the immune system. This is where a population of white blood cells – the B-lymphocytes – matures, which are essential for immune defence.
Physiology
Blood formation begins in the bone marrow from so-called multipotent stem cells. This means that these cells can develop into any other cell. In the case of haematopoiesis, there are two possibilities, since there are two large cell populations.
- The myeloid cell line and the lymphatic cell line. The lymphatic cell series includes the cells of the immune system, the lymphocytes, which belong to the white blood cells.
- The myeloid series includes the red blood cells (erythrocytes), and the blood platelets (thrombocytes). The red blood cells serve to transport oxygen in the body, the platelets are an important component of blood clotting. These finished blood cells develop in the bone marrow via many precursor cells and are finally – when they are mature enough – released into the blood.
