This educational segment provides a microscopic analysis of a stained human bone marrow smear, contrasting it with the composition of peripheral blood. The video highlights the unique characteristics of hematopoietic (blood-forming) tissue, which is approximately 50% fat in the adult axial skeleton. Key cellular components are identified, including the extremely large megakaryocytes (platelet precursors), various stages of the granulocytic (white cell) series, and nucleated normoblasts (red cell precursors). The speaker emphasizes that the white cell precursors outnumber red cell precursors in the marrow, a reversal of the ratio seen in peripheral blood, due to the shorter lifespan of white cells. Detailed visual characteristics of maturing cells, such as the extrusion of the nucleus from normoblasts, are provided.
Analyzing Human Bone Marrow Smears
0:20 Bone Marrow Staining: The preferred stain for bone marrow smears is typically a modification of the Giemsa stain (g.i.m.s.a.), which is similar to the Wright stain used for peripheral blood but offers improved clarity.
0:48 Low Power View/Marrow Composition: The smear on low power shows round, white areas representing fat. The adult bone marrow (specifically in the axial skeleton) is roughly 50% fat and 50% cellular precursors.
1:19 Megakaryocytes (Platelet Precursors): Very large cells, sometimes 50 times the size of surrounding cells, are identified as megakaryocytes. These are the precursors to platelets and are characterized by a tremendous amount of fuzzy cytoplasm.
2:03 Reversed Cell Ratio (WBC vs. RBC): Unlike the peripheral blood smear where red cells vastly outnumber white cells, the bone marrow shows a reversed ratio, with white cell precursors (granulocytes) being more common. This is necessary because white cells have a much shorter lifespan and require faster turnover.
2:25 White Cell Series (Granulocytes): Cells possessing coarse granules are generally part of the white cell series, specifically the granulocytic series (neutrophils, eosinophils, basophils). An eosinophil precursor is identified by its red granules and bilobed nucleus.
3:00 Red Cell Precursors (Normoblasts): Cells with a round nucleus and very dark blue cytoplasm are normalblasts (red cell precursors). As these cells mature (3:20), their nucleus becomes smaller, darker, and is eventually extruded (3:51) to produce a mature red blood cell.
4:33 Monocyte and Lymphocyte Precursors: A large, open, non-lobulated cell is suggested to be a monocyte precursor. Small, round cells exhibiting a characteristic "lip of blue cytoplasm" are likely lymphocytes.
5:36 Key Takeaway: Hematopoietic Marrow: In adults, the marrow of the axial skeleton is hematopoietic, consisting of about 50% fat and 50% precursor cells for red cells, white cells, and platelets.