Bone Marrow and Blood Formation

     Bones are not solid but instead are made up of two distinct regions. The outter weight bearing area is hard compact and calcium based. It surrounds a lattice work of fibrous bone known as cancellous tissue. The inner region, or marrow,which is one of the largest organs in the body, is located inside the bones.It fills the shafts of the long bones and continues down to the boney canals that hold the blood vessels.

     Bone marrow may contain fat cells, fluid, fibrous material, blood vessels and blood forming cells. Marrow appears yellow in color when it holds many fat cells and red when it has more blood forming cells.
     The marrow is the principle site for blood formation which occurs primarily in the bones of the legs, arms, ribs, breastbone and spine.

Stem Cells

     Many of the blood cells that comprise the bloodstream within the arteries and veins are born and mature within the bone marrow. They are derived from hematopoietic cells that are called stem cells.Stem cells within the bone marrow continuously divide to form new cells. Some of the new cells remain unchanged as stem cells and have a lifelong capacity for self-renewal. These cells are called pluripotential cells. Other unipotential have a limited capacity for self-renewal. Also known as progenitors cells, unipotential cells become committed to forming only one type of blood cell line - erythocytes ( redblood cells ), leukocytes ( whiteblood cells ), or platelets. Colonies of progenitor cells of increasing differentiation (maturity). They react to different specfic compounds known as protiens. Proteins stimulate the progenitor cells until they transform into the appropriate young blood cell known as a "Blast" cell.