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Bone marrow is a semi-solid tissue found within the spongy (also known as cancellous) portions of bones. [2] In birds and mammals, bone marrow is the primary site of new blood cell production (or haematopoiesis). [3] It is composed of hematopoietic cells, marrow adipose tissue, and supportive stromal cells.
Myeloid tissue, in the bone marrow sense of the word myeloid (myelo-+ -oid), is tissue of bone marrow, of bone marrow cell lineage, or resembling bone marrow, and myelogenous tissue (myelo-+ -genous) is any tissue of, or arising from, bone marrow; in these senses the terms are usually used synonymously, as for example with chronic myeloid ...
Located in the main shaft of a long bone (consisting mostly of compact bone), the medullary cavity has walls composed of spongy bone (cancellous bone) and is lined with a thin, vascular membrane . [1] [2] This area is involved in the formation of red blood cells and white blood cells, and the calcium supply for bird eggshells. The area has been ...
These cells descend from the primitive reticulum cells, which are found in the stroma of the marrow. There is also an intermediate phase between the myeloblast and these primitive reticulum cells, namely the hemocytoblast. At this time several developing blood cell lines are available, like erythropoiesis and thrombopoiesis.
Bone marrow, also known as myeloid tissue in red bone marrow, can be found in almost any bone that holds cancellous tissue. In newborns , all such bones are filled exclusively with red marrow or hematopoietic marrow, but as the child ages the hematopoietic fraction decreases in quantity and the fatty/ yellow fraction called marrow adipose ...
When bone marrow develops, it eventually assumes the task of forming most of the blood cells for the entire organism. [3] However, maturation, activation, and some proliferation of lymphoid cells occurs in the spleen, thymus, and lymph nodes. In children, haematopoiesis occurs in the marrow of the long bones such as the femur and tibia.
This process indicates that, subsequent to bone marrow transplantation, symmetrical cell divisions into two daughter hematopoietic stem cells must occur. Stem cell self-renewal is thought to occur in the stem cell niche in the bone marrow, and it is reasonable to assume that key signals present in this niche will be important in self-renewal. [2]
Endosteal niche-the outer edge of the bone marrow that contains osteocytes, bone matrix, and quiescent HSCs. Perivascular niche-the inner core of the bone marrow that contains actively dividing HSCs, sinusoidal endothelium, CARs (CXCL12-abundant reticular cells), and MSCs (Mesenchymal stem cells).