Csontvel

Bone marrow (csontvelő in Hungarian) is the soft tissue inside bones where most blood cells are formed. It exists in two main forms: red marrow, which contains hematopoietic tissue, and yellow marrow, which is largely adipose tissue. In children, red marrow fills many bones; in adults, it is concentrated in the pelvis, spine, ribs, skull, sternum, and the proximal ends of the femur and humerus, with the rest of the marrow being yellow.

The primary function of red marrow is hematopoiesis—the production of red blood cells, white blood cells, and platelets. This process is supported by a specialized marrow microenvironment that includes stromal cells, osteoblasts, adipocytes, macrophages, and an extracellular matrix. Growth factors and cytokines, such as erythropoietin and colony-stimulating factors, regulate the development and release of blood cells. The marrow’s vascular network provides nutrients and a route for newly formed cells to enter circulation.

Clinical relevance includes diagnostic and therapeutic procedures. Bone marrow aspiration and biopsy are used to diagnose hematologic disorders and to monitor treatment. Hematopoietic stem cells residing in marrow can be collected for transplantation to replace diseased marrow; transplants may be autologous (patient’s own cells) or allogeneic (donor cells). Diseases affecting marrow include leukemias, lymphomas, myelodysplastic syndromes, aplastic anemia, and other disorders of blood formation.

Aging leads to a gradual replacement of red marrow by yellow marrow, reducing hematopoietic capacity. In certain conditions, yellow marrow can revert to red marrow to meet increased blood cell needs. Imaging and histological analysis aid in assessing marrow structure and function.