Anatomy and morphology of normal bone marrow

• Anatomy

  • Bony trabeculae

  • Network of thin-walled sinusoids lined by endothelial cells, through which differentiated cells enter the blood stream

  • Clusters of fat cells (yellow marrow) and hematopoietic cells (red marrow) are supported by a reticulin meshwork (red marrow is everywhere in a newborn’s skeleton, but is only found in the axial skeleton of adults)

  • The release of mature blood cells into the bloodstream is regulated by endothelial cells lining the marrow sinusoids (this isn’t found in extramedullary hematopoiesis, so immature cells will be found in the peripheral blood if that is going on)

• Morphology

  • There should be progressive maturation of all blood cell lines

  • Non-hematopoietic bone marrow elements

    • Osteoblasts – look like plasma cells, but plasma cells don’t have nuclei, granular pink cytoplasm, or line up next to the trabeculae

    • Osteoclasts – multinucleated (that’s how you can tell them from megakaryocytes)

Category: Medical Subject Notes , Pathology Notes