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Chapter 3 • Red Blood Cell Production, Function, and Relevant Red Blood Cell Morphology 37
36 Part I • Basic Hematology Principles
the red blood cell to survive for its 120-day life cycle, the following conditions are necessary: • The red blood cell membrane must be deformable, able to squeeze though smaller diameter blood vessels • Hemoglobin structure and function must be adequate • The red blood cell membrane must maintain osmotic balance and permeability The mature red blood cell is an anucleate structure with no capacity to synthesize protein, but it is capable of a limited metabolism that enables it to survive for 120 days. 3 An intact, competent, and fully functioning red blood cell membrane is an essential ingredient to a successful red blood cell life span. The membrane of the red blood cell is a trilaminar and three-dimensional structure containing glycolipids and glycoproteins on the outermost layer directly beneath the red blood cell membrane surface. Cholesterol and phospholipids form the central layer, and the inner layer, the cytoskeleton, contains the specific membrane proteins: spectrin, ankyrin, actin, and protein 4.1 (Fig. 3.8). Composition of Lipids in the Interior and Exterior Layers Fifty percent of the red blood cell membrane is protein, 40% is lipid, and the remaining 10% is cholesterol (Box 3.1). The lipid fraction is a two-dimensional interactive fluid that serves as a barrier to most water-soluble
RED BLOOD CELL MEMBRANE DEVELOPMENT AND FUNCTION
The mature red blood cell is a magnificently designed instrument for hemoglobin delivery. As a hemoglobin- filled sac, the red blood cell travels more than 300 miles through the peripheral circulation, submitting itself to the swift waters of the circulatory system, squeezing through the threadlike splenic sinuses, and bathing in the plasma microenvironment. Cellular and environ- mental factors contribute to red blood cell survival. For
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FIGURE 3.3 Basophilic normoblast. From Glassy EF, ed. Color Atlas of Hematology: An Illustrated Field Guide Based on Proficiency Testing. Northfield, IL: College of American Pathologists; 1998. Reproduced with permission.
FIGURE 3.4 Polychromatophilic normoblast. Courtesy of Bernardino Madsen, Casper College, Casper, Wyoming.
• Polychromatophilic normoblast (Fig. 3.4) Size: 13 μ m N:C ratio: 4:1 Nuclear chromatin: Condensed, moderately compacted, smaller in amount, deeper texture Cytoplasm: Color mixture, blue layered with tinges of orange-red, “the dawn of hemoglobinization” as hemoglobin begins to be synthesized, more cytoplasm • Orthochromic normoblast (Fig. 3.5) Size: 8 μ m N:C ratio: 1:1 Nuclear chromatin: Dense, velvet-appearing homogeneous chromatin, baseball round in appearance Cytoplasm: Increased amount with noticeable color change, with orange-red color tinges with slight blue tone • Reticulocyte (polychromatic macrocyte) (Fig. 3.6) Size: 8 μ m Appearance: Remnant of RNA visualized as reticulum, filamentous structure in chains or as a single dotted structure in new methylene
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FIGURE 3.7 Normal red blood cell. Note discocyte shape and small area of central pallor. Courtesy of Kathleen Finnegan, Stony Brook University, Stony Brook, New York.
FIGURE 3.5 Orthochromic normoblast. Courtesy of Kathleen Finnegan, Stony Brook University, Stony Brook, New York.
Antigen
GpA
Protein
Membrane surface
GpB
Lipid bilayer
Membrane cytoskeleton
blue stain, seen in Wright’s stain as large bluish red blood cells, polychromatophilic macrocytes
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• Mature red blood cell (Fig. 3.7) Size: 6 to 8 μ m Appearance: Disk-shaped cell filled with
Actin
Spectrin dimer-dimer interaction
Ankyrin
Adducin
Spectrin
Protein 4.1
hemoglobin, having an area of central pallor of 1 to 3 μ m
FIGURE 3.8 Red blood cell membrane. Note placement of integral proteins (glycophorins GpA and GpB) versus peripheral proteins (spectrin and ankyrin).
FIGURE 3.6 Reticulocyte with new methylene blue. Courtesy of Bernardino Madsen, Casper College, Casper, Wyoming.
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