Human Structure Virtual Histology
    Blood Cells and Hematopoiesis

    Review the table below describing the characteristics and functions of mature white blood cells (WBCs or leukocytes). It is useful to keep in mind the normal differential counts of WBCs in the circulation for a variety of reasons. When looking at blood smears, this knowledge will help you gage how often you might expect to find the various cell types (e.g. neutrophils and lymphocytes are relatively easy to find, while basophils are much harder to locate).

    Examine a human peripheral blood smear, containing mature red blood cells (RBCs, erythrocytes) and leukocytes. This smear was prepared with polychromatic Wright's stain, which stains both basophilic and acidophilic cellular components.

    • Identify the red blood cells, which are the most numerous cells in the smear as they represent ~37-52% of the formed elements in blood. RBCs have a uniform diameter of ~7 um and can be found in the capillaries of most tissues. Their size provides a “histological ruler” by which to estimate sizes of other cells and tissue structures.
    • Study the RBCs closely in the slide and image at the right. Note the intense eosinophilia and lack of basophilia within the cytoplasm due to the presence of abundant hemoglobin and absence of rER, respectively. Also, notice the central pallor of the RBC. This feature results from the RBC’s unique biconcave shape that facilitates gas exchange.

    Clinical note: Anemia is the term applied to any significant reduction in the total mass of erythrocytes or in their content of hemoglobin. Iron-deficiency anemia results from having too little iron available for hemoglobin synthesis. The hereditary disease sickle-cell anemia involves a mutation that produces a single amino acid substitution in hemoglobin, which makes the protein crystallize within erythrocytes at low-oxygen tensions. This alters the cells overall shape and can lead to microvascular blockage and various other problems.

    Now let's take a look at some white blood cells.