LEUKOPOIESIS

• Leukopoiesis can be divided into two major categories:

  myelopoiesis and lymphopoiesis
• are a group of leukocytes whose cytoplasm is filled with granules

  Granulocytes
• Mononuclear cells are categorized into monocytes and lymphocytes
• Mononuclear cells are categorized into monocytes and lymphocytes. These cells have nuclei that are not segmented but are round, oval, indented, or folded.
• folded. The overall function of

  leukocytes is in mediating immunity, either innate (nonspecific), as in phagocytosis by neutrophils, or specific (adaptive), as in the production of antibodies by lymphocytes and plasma cells.
• Myeloblast

  • Measures 15 to 20 um

  • 0% to 3% of the nucleated cells in the bone marrow

  • Deeply basophilic cytoplasm

  • Round/Oval nucleus

  • N:C Ratio is 4:1

  • They are frequently subdivided into type I, type II, and type III myeloblasts
• Promyelocyte

  • Measures 15 to 21 um

  • 1% to 5% of the nucleated cells in the bone marrow.

  • Nucleus is round to oval and is often eccentric

  • Cytoplasm full of Azurophilic granules (Primary) and deeply basophilic

  • N:C Ratio is 3:1 to 2:1
• Neutrophilic myelocyte Measures 15 to 18 um in diameter
• Neutrophilic myelocyte 6% to 17% of the nucleated cells in the bone marrow
• Specific granules (Secondary)

  Neutrophilic myelocyte
• First stage of Granulocytic differentiation

  Neutrophilic myelocyte
• “Juvenile cells”

  Neutrophilic metamyelocyte
• Little to no basophilia

  Neutrophilic metamyelocyte
• Synthesis of Gelatinase granules (Tertiary)

  Neutrophilic metamyelocyte
• Kidney shaped nucleus

  Neutrophilic metamyelocyte
• 3% to 20% of the nucleated cells in the bone marrow

  Neutrophilic metamyelocyte
• No basophilia

  Neutrophilic band
• Secretory granules may begin to be formed during this stage

  Neutrophilic band
• Nucleus is curved; Sausage-shaped


  Neutrophilic band
• 0% to 5% of the nucleated peripheral blood cells


  Neutrophilic band
• 9% to 32% of the nucleated cells in the bone marrow


  Neutrophilic band
• Neutrophilic band

  • Measures 9 to 15 um in diameter
• Segmented neutrophils

  Polymorphonuclear neutrophil
• Pink to Rosy-violet granules


  Polymorphonuclear neutrophil
• Nucleus has 2 to 5 lobes


  Polymorphonuclear neutrophil
• Polymorphonuclear neutrophil / Segmented neutrophils

  • Measures 9 to 15 um in diameter

  • 7% to 30% of the nucleated cells in the bone marrow

  • 50% to 70% of leukocytes in peripheral blood cells
• Polymorphonuclear neutrophil / Segmented neutrophils Hypersegmentation is due to Vitamin B12 deficiency
• The major function of neutrophils is phagocytosis and destruction of foreign material and microorganisms.
• The major function of neutrophils is phagocytosis and destruction of foreign material and microorganisms. The process involves seeking (chemotaxis, motility, and diapedesis) and destruction (phagocytosis and digestion)
• Neutrophil recruitment to an inflammatory site begins when chemotactic agents bind to neutrophil receptors.
• Ingestion

  • Pseudopodia are extended around the foreign particle and enclose it within a “phagosome” (engulfment). The phagosome is pulled toward the center of the cell by polymerization of actin and myosin and by microtubules.
• Oxygen Dependent – Respiratory burst through the activation of

  NADPH oxidase
• They are produced during Oxygen Dependent

  H2O2 and hypochlorite
• The pH within the phagosome becomes alkaline and then

  neutral, the pH at which digestive enzymes work.

  Oxygen Independent
• Primary and secondary lysosomes

  (granules) fuse to the phagosome and empty hydrolytic enzymes and other bactericidal molecules into the phagosome.

  Oxygen Independent
• Large, pale, reddish-orange secondary granules with azure granules

  Eosinophil myelocyte
• Granules containing major basic protein

  Eosinophil myelocyte
• Electron microscopy indicates the presence of two other organelles: lipid bodies and small granules

  Eosinophil metamyelocyte and bands
• Usually display a bi-lobed nucleus

  Mature Eosinophils
• Mature Eosinophils Cytoplasm contains characteristic refractile, orange-red secondary granules