Human Anatomy Part 2 - K. A. Diubenko A. K. Kolomiitsev Yu. B. Chaikovskyi 2008

Special Part
Hematopoietic and Immune Organs - General Information
Primary lymphoid organs {organa lymphoidea primaria} - Bone marrow

Bone Marrow, medulla ossium, is divided into red, medulla ossium rubra, and yellow, medulla ossium flava.

Cytology/practical/86.html">Red bone marrow is one of the primary hematopoietic (hemocytopoietic) Organs. It contains Embryonic Stem Cells (Fig. 114). Red bone marrow is located in the spongy bone, substantia spongiosa, of flat bones, predominantly in the Sternum, scapula, BONES OF THE cranial vault, vertebrae, Ribs, pelvic bones, the epiphyses of long bones, and the medullary cavities, cavum medullare. The color of red marrow is due to the vast number of erythrocytes it produces.

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Fig. 114. Red bone marrow, medulla ossium rubra (diagram)

Yellow bone marrow, medulla ossium flava, is located in the diaphyses of long bones. It contains numerous fat cells (adipocytes) containing a pigment (lipochrome), which gives this section of the bone marrow its yellow color and accounts for its name. Yellow bone marrow does not perform a hematopoietic function. Children's bones contain only red bone marrow. At approximately 12-18 years of age, it is replaced by yellow marrow in the diaphyses.

In an adult, bone marrow accounts for approximately 4.5-4.7 % of body weight, half of which is red marrow. The stroma of red bone marrow is formed by Blood Vessels (Arteries, arterioles, capillaries, sinusoids, venules) and reticular Connective Tissue. Within the framework of the latter, parenchymal elements are located: hematopoietic elements and stem cells, which, despite being relatively few in number, are the progenitors of all blood and immunocompetent cells. The parenchyma of red marrow consists of erythrocytes, granulocytes, monocytes, platelets, and lymphocytes at various Selection/3.html">Stages of development.

Blood vessels and the reticular connective tissue of red bone marrow, along with providing supportive and trophic Functions, form the so-called microenvironment that promotes myelopoiesis—The formation of Blood Cells (myelos - marrow, poiein - to make).

Blood supply. Bone marrow is supplied with blood via blood vessels that penetrate it through the nutrient foramina of the compact bone. Red bone marrow is highly sensitive to ionizing radiation. Exposure to excessive doses of radiation leads to hematopoietic disorders, which sometimes require bone marrow transplantation in specialized hospitals, among other treatments.