Nada Mohamed Ahmed, MD, MT (ASCP)i LEC 3

Objectives Definition Types of leucocytes Leucopoiesis stages Normal morphology of WBCs (structure &function)

Definition leukopoiesis – production and developments of white blood cells(leucocytes)

Leukopoiesis leaves Lymphoblast B prolymphocyte B lymphocyte T lymphocyte NK cell T prolymphocyte NK prolymphocyte MonoblastPromonocyteMonocyte Basophil Eosinophil Neutrophil Pluripotent stem cell Colony-forming units (CFUs) Precursor cells Mature cells Eosinophilic myelocyte Eosinophilic promyelocyte Eosinophilic myeloblast Eosinophilic CFU Basophilic CFU Neutrophilic CFU Monocytic CFU Lymphocytic CFU Basophilic myeloblast Neutrophilic myeloblast Neutrophilic promyelocyte Basophilic promyelocyte Basophilic myelocyte Neutrophilic myelocyte

White Blood Cells (Leukocytes) ____________________________ Formation of Leukocytes (Leukopoiesis): All in bone marrow Pluripotent stem cells Myeloblast lymphoblast ↓ Myeloid line Lymphoid line - Granulocytes Lymphocytes - Monocytes

Formation of Leukocytes Figure

Formation of Leukocytes All leukocytes originate from hemocytoblasts Hemocytoblasts differentiate into myeloid stem cells and lymphoid stem cells Myeloid stem cells become myeloblasts or monoblasts Lymphoid stem cells become lymphoblasts Myeloblasts develop into eosinophils, neutrophils, and basophils Monoblasts develop into monocytes Lymphoblasts develop into lymphocytes

Formation of Leukocytes leukopoiesis – production of white blood cells pluripotent stem cells – (PPSCs) myeloblasts – form neutrophils, eosinophils, basophils monoblasts - form monocytes lymphoblasts give rise to all forms of lymphocytes

Production of Leukocytes Leukopoiesis is hormonally stimulated by two families of cytokines (hematopoetic factors) – interleukins and colony-stimulating factors (CSFs) – Interleukins are numbered (e.g., IL-1, IL-2), whereas CSFs are named for the WBCs they stimulate (e.g., granulocyte-CSF stimulates granulocytes) Macrophages and T cells are the most important sources of cytokines Many hematopoietic hormones are used clinically to stimulate bone marrow

Types of Leukocytes Granulocytes Neutrophils (60-70%)-polymorphonuclear leukocytes barely-visible granules in cytoplasm; 3 to 5 lobed nucleus Eosinophils (2-4%) arge rosy-orange granules; bilobed nucleus Basophils (<1%) large, abundant, violet granules (obscure a large S-shaped nucleus)

Granulocytes Neutrophils 10 µm Eosinophil 10 µm Basophil 10 µm

Agranulocytes lymphocytes (25-33%) variable amounts of bluish cytoplasm (scanty to abundant); ovoid/round, uniform dark violet nucleus monocytes (3-8%) largest WBC; ovoid, kidney-, or horseshoe- shaped nucleus

Agranulocytes Lymphocyte 10 µm Monocyte 10 µm

Characteristics of Mature Leukocytes (WBCs) Least Abundant Formed Element – 5,000 To 10,000 Wbcs/  L Protect Against Infectious Microorganisms And Other Pathogens Conspicuous Nucleus Spend Only A Few Hours In The Blood Stream Before Migrating To Connective Tissue Retain Their Organelles For Protein Synthesis granules – All WBCs have lysosomes called nonspecific (azurophilic) granules – inconspicuous so cytoplasm looks clear – Granulocytes have specific granules that contain enzymes and other chemicals employed in defense against pathogens

Leucocytes migration Circulating Wbcs Do Not Stay In Bloodstream – granulocytes leave in 8 hours and live 5 days longer – Monocytes leave in 20 hours, transform into macrophages and live for several years – Lymphocytes provide long-term immunity (decades) being continuously recycled from blood to thymus gland and back to the blood

Granulocyte Functions Neutrophils – phagocytosis of bacteria – release antimicrobial chemical increased numbers in bacterial infections Eosinophils initiate allergic reaction – release enzymes to destroy large parasite – i ncreased numbers in parasitic infections Basophils – secrete histamine (vasodilator) – speeds flow of blood to an injured area – produce inflammatory mediators

Agranulocyte Functions Lymphocytes – destroy cells (cancer, foreign, and virally infected cells) – coordinate actions of other immune cells – secrete antibodies and provide immune memory increased numbers in viral infections and inflammation Monocytes – leave bloodstream and transform into macrophages phagocytize pathogens and debris “present” antigens to activate other immune cells - antigen presenting cells (APCs) increased numbers in diverse infections and immune responses

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