Histology of Blood Cells

• Erythrocytes (Red Blood Cells)
• Anemia: Decrease of concentration of the erythrocytes in the blood
• Erythrocytosis or polycythemia: Increase number of red blood cells in the blood, generally related to physiological situations
• Macrocytes: Greater than 9 μm
• Microcytes: Less than 6 μm
• Anisocytosis: Cells vary greatly in size
• Integral membrane proteins represent most of the proteins in the lipid bilayer
• Glycophorins play an important role in attaching the cytoskeletal protein network to the cell membrane
• Band 3 binds hemoglobin and acts as an additional anchoring site for the cytoskeletal proteins
• Peripheral membrane proteins reside on the inner surface of the cell membrane and are mainly composed of cytoskeletal proteins including spectrin, tetramers, actin, band 4.1 protein
• Life span of erythrocytes is about 120 days
• Sickle cell disease is caused by a single-point mutation in the gene that encodes the β-globin chain of hemoglobin A
• Leukocytes (White Blood Cells)
• Granulocytes: Neutrophils, Eosinophils, Basophils
• Agranulocytes: Lymphocytes, Monocytes
• Neutrophils constitute 60-70% of circulating leukocytes
• Neutrophils have nuclei consisting of 2-5 lobes, with hypersegmented cells having more than 5 lobes
• Neutrophils contain specific granules (secondary granules) and azurophilic granules (primary granules)
• Eosinophils are about the same size as neutrophils, with bilobed nuclei
• Eosinophils play a major role in host defense against helminthic parasites
• Basophils have numerous large granules in their cytoplasm that stain with basic dyes
• Lymphocytes
• Second most numerous white cells in the blood
• Numbers increase in response to viral infections
• Most important cells in immune response
• Three functionally distinct types of lymphocytes: T lymphocytes, B lymphocytes, and NK cells
• Mature lymphocytes approximate the size of an erythrocyte in blood smears
• Plasma cells secrete large amounts of antibodies
• Memory cells and Helper T cells stimulate T and B lymphocytes in their response to antigens
• Plasma cells secrete a large amount of antibodies
• Memory cells
• Helper T cells secrete factors that stimulate T and B lymphocytes in their response to some antigens
• Suppressor T cells dampen responses to foreign antigens and play a key role in suppressing responses to self-antigens
• Cytotoxic T cells destroy transplanted and other foreign cells as well as virus-invaded cells by making holes in their membranes, through which the cell contents leak out
• Memory T cells remain inactive but are primed to respond more rapidly and to a greater extent upon subsequent exposure to the specific antigen
• NK cells are programmed during their development to kill certain virus-infected cells and some types of tumor cells
• NK cells also secrete an antiviral agent, interferon (IFN-)
• Monocytes are the precursors of the cells of the mononuclear phagocytic system
• Monocytes transform into macrophages, which function as antigen-presenting cells in the immune system
• During inflammation, the monocyte leaves the blood vessel at the site of inflammation, transforms into a tissue macrophage, and phagocytoses bacteria, other cells, and tissue debris