Photomicrograph of a sickle cell anemia blood smear. Blood smear stained with Wright's stain shows abnormal "boat" and "sickle'-shaped cells from an Individual with sickle cell anemia. X400.
in slightly higher percentages than normal in sickle cell disease and thalassemia, it does not appear to have a pathologic role. A monomer of hemoglobin is similar in composition and structure to myoglobin, the oxygen-binding protein found in striated muscle.
Leukocytes are subclassified into two general groups. The basis for this division is the presence or absence of prominent specific granules in the cytoplasm. Cells containing specific granules are classified as granulocytes (neutrophils, eosinophils, and basophils), and cells that lack specific granules are classified as agranulocytes (lymphocytes and monocytes). However, both agranulocytes and granulocytes possess small, nonspecific azurophilic granules, which are lysosomes. The relative number of the various leukocytes is given in Table 9.1.
Neutrophils are the most numerous WBCs as well as the most common granulocyte
Neutrophils measure 10 to 12 pm in diameter in blood smears and are obviously larger than erythrocytes. Although named for their lack of characteristic cytoplasmic staining, they are also readily identified by their multilobed nucleus; thus, they are also called polymorphonuclear neutrophils or polymorphs. Mature neutrophils possess two to four lobes of nuclear material joined by thinner nuclear strands. The arrangement is not static; rather, in living neutrophils the lobes and connecting strands change their shape, position, and even number.
The chromatin of the neutrophil has a characteristic arrangement. Wide regions of heterochromatin are located chiefly at the periphery of the nucleus, in contact with the nuclear envelope. Regions of euchromatin are located chiefly at the center of the nucleus, with relatively smaller regions contacting the nuclear envelope (Fig. 9.7). In females, the Barrbody forms a drumstick-shaped appendage on one of the nuclear lobes.
The cytoplasm of a neutrophil contains three kinds of granules. The different types of granules reflect the various phagocytotic functions of the cell:
• Specific granules (secondary granules) are the smallest granules and are at least twice as numerous as azurophilic granules. They are barely visible in the light microscope; in electron micrographs they are ellipsoidal (see Fig. 9.7). Specific granules contain various enzymes (type IV collagenase, phospholipase) as well as complement activators and other bacteriostatic and bactericidal agents (lysozyme).
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