Bone Marrow Structure
Bone marrow is separated into a vascular section and non-vascular sections. The vascular section contains blood vessels that supply the bone with nutrients and transport blood stem cells and mature blood cells away from the bone and into circulation. The non-vascular sections of the bone marrow are where hematopoiesis or blood cell formation occurs. This area contains immature blood cells, fat cells, white blood cells (macrophages and plasma cells), and thin, branching fibers of reticular connective tissue. While all blood cells are derived from bone marrow, some white blood cells mature in other organs such as the spleen, lymph nodes, and thymus gland. Most hematopoietic stem cells are found in the bone marrow which gives it a need to keep in good condition while working on a healthy aging process.
Bone Marrow Function
The major function of bone marrow is to generate blood cells. Bone marrow contains two main types of stem cells. Hematopoietic stem cells, found in red marrow, are responsible for the production of blood cells. Bone marrow mesenchymal stem cells (multipotent stromal cells) produce the non-blood cell components of marrow, including fat, cartilage, fibrous connective tissue (found in tendons and ligaments), stromal cells that support blood formation, and bone cells.
In adults, red marrow is confined mostly to skeletal system bones of the skull, pelvis, spine, ribs, sternum, shoulder blades, and near the point of attachment of the long bones of the arms and legs. Not only does red marrow produce blood cells, but it also helps to remove old cells from circulation. Other organs, such as the spleen and liver, also filter aged and damaged blood cells from the blood. Red marrow contains hematopoietic stem cells that produce two other types of stem cells: myeloid stem cells and lymphoid stem cells. These cells develop into red blood cells, white blood cells, or platelets.
Yellow marrow consists primarily of fat cells. It has poor vascular supply and is composed of hematopoietic tissue that has become inactive. Yellow marrow is found in spongy bones and in the shaft of long bones. When blood supply is extremely low, yellow marrow can be converted to red marrow in order to produce more blood cells
Red bone marrow contains hematopoietic stem cells that produce two other types of stem cells: myeloid stem cells and lymphoid stem cells. These cells develop into red blood cells, white blood cells, or platelets.
Myeloid Stem Cells – develop into red blood cells, platelets, mast cells, or myeloblast cells. Myeloblast cells develop into granulocyte and monocyte white blood cells.
Lymphoid Stem Cells – develop into lymphoblast cells, which produce other types of white blood cells called lymphocytes. Lymphocytes include natural killer cells, B lymphocytes, and T lymphocytes.