[NORMAL BONE MARROW]. A core biopsy section of an adult bone marrow is shown. Bone marrow is the spongy portion inside bones and consists of a meshwork of bone trabeculae (big arrow) containing hematopoietic marrow elements and fat cells (arrowhead). The ratio of hematopoietic elements versus fat cells depends on the age and activity of bone marrow in response to various physiologic stimuli. Marrow cellularity is roughly inversely proportion to the age. Thus, newborns have almost 100% cellular bone marrow whereas older individuals in their eighth or ninth decades have 20-30% cellularity. This marrow is from an 54-year-old individual.
[NORMAL BONE MARROW]. Bone marrow is the organ where all the blood cells are made from stem cells in the post-natal life under normal physiologic mechanisms. The fat cells (arrowhead) are dispersed throughout the marrow among hematopoietic elements (long thin arrow) and their number increase or decrease according to the hematopoietic activity of the marrow. The bone trabeculae provide a network of supportive framework for hematopoiesis to occur.
[NORMAL BONE MARROW]. A normal marrow is said to show trilineage hematopoiesis (TLH) meaning that elements of all three major cell lines are represented. These cell lines include myelomonocytic cells, erythroid cells, and megakaryocytic cells. However, other cells types are also present including lymphocytes, plasma cells, connective tissue cells and stromal cells. Two histiocytes are present (arrowheads) engulfing cellular debris. The nucleated erythroid precursors are also dispersed (two long arrows) throughout the marrow. Two normal megakaryocytes are apparent in this field (two big arrows). A binucleated eosinophil is identified with an arrow with tail.
[NORMAL BONE MARROW]. A normal megakaryocyte is multilobated with up to 48N of DNA amount. This is the result of endo-mitosis where nucleus continues to double chromosome number but the cell does not divide. Note a mature megakaryocyte shows a multilobated nucleus (left arrowhead) and abundant pink cytoplasm whereas a young (nascent) megakaryocytes shows a nucleus with folded nuclear lobes and little cytoplasm (up arrow).
[NORMAL BONE MARROW]. A paratrabecular portion of the bone marrow is shown where most of the immature myeloid elements are found including normal myeloblasts. This region is supposed to contain hematopoietic stem cells which upon appropriate stimuli mature into different cell types. When cells mature they move away from the paratrabecular location giving rise space for new immature cells. Note the bone trabeculae (big arrow) and immature myeloid cells (thin arrow) and an erythroid precursor (arrowhead). A neutrophil is present away from the bone trabeculae (arrow with tail).
[NORMAL BONE MARROW]. Mature normal bone marrow cells are shown in the center of the inter-trabecular space. Squiggly arrow = A band neutrophil; arrow with tail = Segmented neutrophils; arrowhead = plasma cell; thin arrow = nucleated red cell.
[NORMAL BONE MARROW]. A bone marrow section showing an arteriole (arrowhead) and a large venous sinus (long arrow). The arteriole provides blood supply to the marrow whereas the venous sinus a collection system within the marrow where mature cells enter the circulation for the very first time including segmented neutrophils, basophils, eosinophils, red blood cells, monocytes, and platelets. This is how cells enter the general circulation from areas of hematopoiesis in the marrow.
[NORMAL BONE MARROW]. This slide is a normal bone marrow aspirate smear. Note large darker clump of cells (lower arrow) enmeshed in stromal cells and other connective tissue cells that is called a “spicule.” A spicule is bordered by marrow cells that are more thinly spread out (arrowhead) where morphologic examination of the marrow cells is performed. The spicule is too thick to be adequate for morphologic examination. Note also fat cells (thin long arrow) on the aspirate smear.
[NORMAL BONE MARROW]. This marrow aspirate smear shows normal hematopoietic elements with a myeloid to erythroid ratio (ME ratio) of about 3:1. The ME ratio indicates the proportion of myeloid elements including all their precursors in relation to the number of nucleated erythroid precursors. Mature red blood cells without nuclei are not counted. In normal adults there are about 3-4 myeloid elements to every single nucleated erythroid element. This ratio is altered in many disease states including hemolytic anemia, agranulocytosis, and myeloproliferative disorders.
[NORMAL BONE MARROW]. This slide shows various normal bone marrow cells. In myeloid series the cells mature in the following order: Myeloblast >> Promyelocyte >> Myelocyte >> Metamyelocyte >> Band neutrophil >>Segmented neutrophil (or eosinophil or basophil). In the erythroid series the cells mature in the following order: Proerythroblast >> Basophilic erythroblast >> Polychromatic erythroblast >> Orthochromatic erythroblast >> Reticulocyte >> Mature red cell. The various cells are as follows: 1 = Myeloblast, 2 = Promyeloocyte, 3 = Myelocyte, 4 = Metamyelocytes, 5 = Band neutrophil, 6 = Segmented neutrophil, 7 = Eosinophil, 8 = Monocyte, 9 =Proerythroblast, 10 = Basophilic erythroblasts, 11 = Polychromatic erythroblast, 12 = Orthochromatic erythroblast, 13 = Lymphocyte.
[NORMAL BONE MARROW]. A myeloblast (#1) is the earliest recognizable cell in the myeloid series and is characterized by scant agranular to sparsely granular cytoplasm and large nucleus with fine chromatin and one to three prominent nucleoli. The quality of chromatin is the most important morphologic feature to identify a myeloblast. A promyelocyte (#2) is the next morphologic stage in myeloid maturation where cells accumulate more cytoplasm and azurophilic granules and the nucleus becomes smaller and show coarser chromatin with small to distinct nucleoli. A monocytes (#3) is shown with abundant cytoplasm and finer and fewer granules than a promyelocytes and no prominent nucleoli. A basophilic erythroblast (#4) is the 2nd individually recognizable stage in erythroid maturation after proerythroblast and is characterized by deeply basophilic cytoplasm and coarser nuclear chromatin without a distinct nucleus. An Orthochromatic erythroblast (#5) is characterized by hemoglobinized cytoplasm and condensed darker nucleus which is about to be extruded from the cell upon maturation. A small lymphocyte (#6) contains very little cytoplasm and shows round nucleus with dense chromatin and no prominent nucleus.
[NORMAL BONE MARROW]. Various marrow cells are shown: 1 = Proerythroblast, 2 = Basophilic erythroblast, 3 = Polychromatic erythroblast, 4 = Promyelocyte, 5 = Myelocyte, 6 = Early band neutrophil, 7 =Late band neutrophil, 8 = Segmented neutrophil, 9 = Band eosinophil, 10 = Monocyte, 11 = Small lymphocyte.
[NORMAL BONE MARROW]. Various marrow cells are shown: 1 = Myelocytes, 2 = Metamyelocyte, 3 = Band neutrophil, 4 = Segmented neutrophil, 5 = Basophilic myelocyte, 6 = mature basophil, 7 = Monocyte, 8 = Small lymphocyte, 9 = Erythroid precursors at various stages of maturation, 10 = Myeloblast.
[NORMAL BONE MARROW]. This image highlights the morphologic difference between a proerythroblast (#1) and a myeloblast (#2). Both are the earliest recognizable stages in their respective series. Note that a proerythroblast has a more basophilic cytoplasm than a myeloblast and nucleoli are generally longer ad curved and “comma-shaped” than myeloblasts’ nuclei which are generally round. Other cells are: 3 = Myeloocyte, 4 = Neutrophil, 5 = Samll lymphocyte, 6 = Smudged cell of unknown lineage.
[NORMAL BONE MARROW]. A difference between a myelocyte (#1) and a monocytes (#2) is highlighted . A myelocyte generally has a lot of cytoplasmic primary granulation and a paranuclear lighter Golgi zone clearing whereas a monocyte has fewer and small granules. Other cells include a polychromatic erythroblast (#3) and an orthochromatic erythroblast (#4).
[NORMAL BONE MARROW]. A mast cell (#1) is shown with abundant basophilic to purple cytoplasmic granulation. A segmented neutrophil (#2) and an orthochromatic erythroblast (#3) is also present.
[NORMAL BONE MARROW]. Various bone marrow cells are shown: 1 = Segmented neutrophil, 2 = Large granular lymphocyte, 3 = polychromatic erythroblast. Large granular lymphocytes are rare in bone marrow (<0.5% of all nucleated cells).
[NORMAL BONE MARROW]. Various marrow cells are shown: 1 = Proerythroblast, 2 = Basophilic erythroblast, 3 = Polychromatic erythroblast, 4 = Lymphocyte, 5 = Plasma cell, 6 = Eosinophil.
[NORMAL BONE MARROW]. Various stages of erythroid maturation are shown: 1 = Proerythroblasts, 2 = Polychromatic erythroblasts, 3 = Orthochromatic erythroblast.
[NORMAL BONE MARROW]. A mature megakaryocyte is shown with multiple nuclear lobes (arrow). Note shedding of cytoplasmic fragments as “platelets” at the peripheral border of the megakaryocyte (long arrow). A metamyelocyte (#1) and a plasma cell #2) are shown.
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