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Blood and Bone Marrow

Objectives

  1. Describe basic histology of bone marrow including the relationship between the endosteum, vascular space, and marrow compartment
  2. Identify stages of hematopoiesis
  3. Identify different types of blood cells

Blood and Bone Marrow Overview

Blood is a specialized type of connective tissue which flows through the body to provide the needed nutrients, oxygen, hormones, immune system components while removing waste elements as well. Blood is made up of cell derivatives with a protein-rich fluid known as plasma:

  • Erythrocytes, or red blood cells (RBCs)- biconcave disc 7-8μm in diameter. Consistent in size in fixed tissue and therefore can be used as a “histologic ruler”. Stain homogeneously with eosin, lack a nucleus. Function: O2/CO2 transport
  • Leukocytes, or white blood cells (WBCs)
    • Agranulocytes (no granules in the cytoplasm other than occasional azurophilic granule (lysosome))
      • Lymphocytes– precursor for T cells, B cells, NK cells; mature lymphocyte is about the size of a RBC (7-8μm in diameter in blood smear), small lymphocytes have an intense-staining nucleus. Function: wound healing, immunity.
        • T cells– differentiate in the thymus gland.
        • B cells– indistinguishable from B cells in typical blood smear or tissue staining, need to use techniques that target cell-surface markers.
        • NK (natural killer) cells– target specific virus-infected cells and tumor cells
      • Monocytes– precursors for phagocytes in various tissues, largest WBC, about 18μm diameter, indented nucleus. Function: wound healing, phagocytosis.
    • Granulocytes (granules present in cytoplasm)
      • Neutrophils– most numerous WBCs, 10-12μm diameter, multi-lobed nucleus (4 lobes in mature cells), presence of Barr body people with XX sex chromosomes, cytoplasm contains 3 types of granules (azurophilic/primary are the largest, specific/secondary are small and difficult to see in light microscopy, tertiary. Function: phagocytosis.
      • Eosinophils10-12μm diameter, bi-lobed nucleus, large eosinophilic granules (primary) which contain crystalloid body and azurophilic/primary granules (lysosomes) found in the cytoplasm. Function: combat parasites, wound healing, chronic infection, allergic reaction.
      • Basophils– least numerous of WBCs, 10-12μm diameter, lobed nucleus obscured by the large granules. Function: allergic reactions (bind IgE), wound healing.
  • Thrombocytes, or platelets- small membrane-bound, anucleate fragments of cytoplasm derived from megakaryocytes. Function: coagulation.

Erythrocytes and granular leukocytes have multiple stages of differentiation from their individual progenitor cells that can be visualized in light microscopy:

Modified from Figure 10.22. Histology: A Text and Atlas: With Correlated Cell and Molecular Biology, 8e, 2020. Copyright © Wolters Kluwer

Each individual granulocyte progenitor cell, erythrocyte progenitor, and megakaryocyte (becomes platelets) progenitor originates from a common myeloid progenitor which differentiates from a hemopoietic stem cell. The different lymphoid cells differentiate from a common lymphoid progenitor which also differentiated from the hemopoietic stem cell.

Figure 10.19. Histology: A Text and Atlas: With Correlated Cell and Molecular Biology, 8e, 2020. Copyright © Wolters Kluwer

The process of hematopoiesis, development of RBCs and WBCs and platelets occurs in red bone marrow and some lymph tissues in the adult. During embryogenesis, the hematopoiesis begins in blood islands of the yolk sac around the third week of gestation followed by the second phase in the liver, mostly during the second trimester. The next phase in fetal development occurs in the bone marrow.

Bone Marrow

Bone marrow can be found in the open spaces of bone such as medullary cavities in long bones and trabeculae of spongy bone. Bone marrow is a type of loose connective tissue filled with adipocytes and developing blood cells. There are two types of marrow: red marrow (active in hematopoiesis) and yellow marrow (inactive in hematopoiesis, adipocytes are predominant). The marrow can be found between the endosteum of trabeculae and vascular endothelium. The sinusoidal capillaries allow passage of mature blood cells from the marrow to the systemic circulation.

Viewing blood and bone marrow

Stain- Romanowsky-type stains such as Wright or Wright-Giemsa are typical to observe blood and bone marrow. These type of stains include eosin and oxidized methylene blue dyes.

Blood smears are an easy way to examine the different types of cells in the circulating blood. A drop of blood is placed on a slide and the cover slip is used to smear the blood. Once dry, the dye is applied.

Bone marrow is collected via a core-needle biopsy, typically from the hip bone or sternum (breast bone). The dyes described above can also be applied to examine the different cell types.

Blood and Bone Marrow Slides

This specimen of a blood smear consists of final derivatives of the hematopoiesis including erythrocytes and different types of leukocytes (granulocytes and agranulocytes). You should find eosinophils, neutrophils, lymphocytes, and monocytes along with many erythrocytes. You may observe some platelets/thrombocytes as well. Basophils are the least numerous and may not be present in this specimen. Use what you’ve learned about the cell characteristics to help you identify the cells. Start by finding red blood cells to use them as a ruler. Then determine if the cell you are observing is larger, smaller or of similar size. Then look at the cytoplasm, is it granular or agranular? If the cytoplasm is granular, what are the colors of the granules and shape of the nucleus?

U. of Cincinnati Blood Smear 100x. There are 4 annotation boxes.

This specimen is similar to the one above and includes red blood cells, granulocytes (eosinophils, neutrophils, basophils) and agranulocytes (lymphocytes, monocytes and platelets).

Loma Linda Long Bone. There are 2 annotation boxes.

In this specimen of a long bone, we can examine the bone marrow. This slide has good examples of megakaryocytes and sinusoids but you will not be able to identify different stages of developing blood cells but should be able to identify adipocytes, megakaryocytes, red blood cells and in general, white blood cells (but not specific stages or types).

Drexel Bone Marrow Smear, 100x. There are 6 annotation boxes.

In this specimen, the bone marrow was removed and smeared on the slide before staining. You will be able to identify cells of different stages of hematopoiesis. Remember to use the fully formed red blood cells as a ruler to distinguish sizes of the cells. Use your knowledge of the cell characteristics including nuclear shape and whether there are granules present in the cytoplasm. Also look at the color of the granules. Refer to the chart above, figure 10.22. Histology Guide website figure on hematopoiesis also provides a good picture summary.

Using this bone marrow smear, practice identifying the different stages of white and red blood cells. Pay attention to the size of cells, shape of nucleus, color of cytoplasm, and color of granules in cytoplasm if present.

More Practice

Iowa Bone Marrow Smear, Giemsa stain. There are 7 annotation boxes.

This bone marrow smear is the same slide as above but looks at different cells. Identify various blood cells including stages of erythrocyte development. Remember to use the mature erythrocytes as a size ruler and look at the cytoplasm of cells to determine if there are granules present.

GWU 07 Blood Smear, Wright Stain. There are 3 annotation boxes.

This blood smear is the same as above but looking at different cells. Use this slide to review mature blood cells found in peripheral blood.

More Practice Answers

Slide Iowa Bone Marrow Smear

  1. A) black- megakaryocyte; B) green- neutrophil
  2. A) black- basophil; B) blue- platelets/thrombocytes
  3. A) black- neutrophil
  4. A) black- eosinophil (red granules, bi-lobed nucleus); B) blue- red blood cell/erythrocyte
  5. A) black- proerythroblast; B) blue- polychromatic erythroblast (very dark nucleus and dark cytoplasm, agranular, similar size to erythrocyte)
  6. orthochromatic erythroblast, notice the size is the same as an erythrocyte and the cytoplasm color is very similar to the erythrocyte
  7. monocyte, notice the cell border is irregular and the cytoplasm is agranular

Slide GWU 07 Blood Smear

  1. A) black- monocyte; B) blue- neutrophil; C) green- platelet
  2. eosinophil
  3. A) black- erythrocyte/RBC; B) blue- neutrophil; C) red- lymphocyte