Haematopoiesis Lab

Learning Objectives

  • Identify the hematopoietic precursor cells of a typical bone marrow smear
  • Differentiate between precursors in granulopoiesis and erythropoiesis.

Lab Content

Introduction

The bone marrow smear can be used to assess the process of hematopoiesis, or blood cell formation. Active bone marrow appears highly cellular. The majority of the developing cells will become erythrocytes, which confer a red color to the marrow. For this reason, active bone marrow is also known as red bone marrow. Over time, the marrow becomes less active and its fat content increases. It is then referred to as yellow bone marrow. Once again, there are several important characteristics to take into account when viewing a bone marrow smear. These include:

  • Size of the cell
  • Cytoplasm to nucleus volume ratio
  • Shape of the nucleus
  • Degree of chromatin condensation
  • Presence or absence of nucleoli
  • Cytoplasmic staining
  • Presence of cytoplasmic granules

Blast Cell

The blast cell is a pluripotent stem cell from which erythrocytes, granulocytes, and lymphocytes originate. Erythrocytes develop from erythryoblasts, granulocytes from myeloblasts, and lymphocytes from lymphoblasts. These cells, however, all appear identical - they are large with round or ovoid nuclei, a distinct nuclear membrane, visible nucleoli, and an abundant blue cytoplasm. As the blast cells differentiate, the resultant cells can be assigned to a particular cell line.

Erythropoiesis

Erythropoiesis is the development of red blood cells. This composite image shows the different stages of erythropoiesis.

  • The erythroblast develops into a proerythroblast, which is only slightly smaller than the blast, but has a more basophilic cytoplasm.
  • The basophilic erythroblast forms when the proerythroblast loses its nucleolus. These cells are much smaller than the blast cells and have an intensely basophilic cytoplasm that results from the accumulation of ribosomes.
  • The polychromatophilic erythroblast has a darkly staining nucleus and its cytoplasm stains a grayish-green color due to the accumulation of hemoglobin.
  • In the orthochromatic erythroblast, or normoblast, the nucleus becomes smaller and darker and the cytoplasm becomes pinker. Nuclear expulsion occurs at the end of this stage through an asymmetric division of the orthochromatic erythroblast. The portion that contains the cytoplasm and organelles becomes the reticulocyte, while the portion containing the nucleus is destroyed by macrophages.
  • The reticulocyte contains cytoplasm, cytoplasmic organelles, and many ribosomes. It is released from the bone marrow and develops into a mature erythrocyte after spending 1 to 2 days in the peripheral blood.

Granulopoiesis

Granulopoiesis is the process by which white blood cells develop. This composite image shows the different stages of granulopoiesis for a neutrophil.

  • The myeloblast differentiates into a promyelocyte that becomes irreversibly committed to the neutrophilic cell line. This cell is large, with a large round nucleus, prominent nucleoli, and purple azurophilic granules. These granules are primary, nonspecific granules. Promyelocytes also give rise to eosinophils and basophils
  • The myelocyte stage is characterized by the production of secondary, specific granules. Myelocytes can vary in cell size and nuclear shape. They contain both the purple staining azurophilic granules and lilac staining specific granules. As they develop, they decrease in size, their nucleus becomes indented, and there is a shift toward more specific granules. There is also a reduction in the number of organelles, which results in decreased basophilia of the cytoplasm.
  • The metamyelocyte has a flattened nucleus with condense chromatin.
  • The band cell has a horseshoe-shaped nucleus that is "immature." As development continues, it will mature into a segmented nucleus with multiple lobes. It will then be a mature neutrophil.
  • Eosinophils and basophils undergo sequential stages of differentiation in a very similar manner to those of neutrophils. Their specific granules are also produced during the myelocyte stage.

Megakaryocytes

The megakaryocyte is the platelet precursor cell. It is a multinucleated cell with numerous azurophilic granules. Large, multilobed promegakaryocytes develop into megakaryocytes, which are the largest cells of the bone marrow (30 to 40 microns). Platelets form through the segmentation of these cells.

Virtual Microscope Slides

  1. Bone Marrow Smear
    2. Identify cells in the different stages of erythropoiesis and granulopoiesis.

Lab Quiz

  1. What changes will take place in the nucleus of this cell?
    2. Answer: Band Cell. Become segmented.
  2. Why is the cytoplasm becoming pink?
    3. Answer: Reduction in ribosomes (blue) and increase in hemoglobin (orange).
  3. Identify the large cell.
    4. Answer: Large cell is a promyeloblast.
  4. Identify theses cells.
    5. Answer: Metamyelocytes