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Leukocytes
- Protect against infectious microorganisms and other pathogens
- Spend only a few hours in the bloodstream
- Unlike RBCs, they have most organelles
- Separated by appearance of "granules" (vesicles and lysosomes)
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Granular Leukocytes
Have large visible vesicles and lysosomes after staining
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Agranular Leukocytes
Have smaller ones that cannot be visualized
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Diapedesis of Leukocytes
- Leukocytes can leave bloodstream by squeezing between endothelial cells of blood vessel wall
- Allows them to enter connective tissue and organs to fight infections
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Chemotaxis of Leukocytes
- Leukocytes are attracted to specific chemical signals
- Guides them to pathogens, damaged tissue, other active WBC
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Phagocytosis by Leukocytes
Leukocytes can "swallow" pathogens and cell debris
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Macrophage
Monocyte that differentiates in a specific tissue for phagocytes
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Microphage
Neutrophils and eosinophils are capable of phagocytosis
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Neutrophils
- 2-5 lobes of nucleus
- Barely visible granules in cytoplasm
- Most abundant leukocyte
- Respond to injuries first
- Increase in number during bacterial infection
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Neutrophil Response to Injury
- 1. Engulfs bacteria
- 2. Produces and releases antimicrobial chemicals to destroy surrounding bacteria
- 3. Produces digestive enzymes that destroy engulfed bacteria
- 4. Secretes prostaglandins to cause inflammation and reduce spread of injury
- 5. Secrete leukotrienes to recruit other phagocytes
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Eosiniphils
- 2 lobed nucleus
- Large granules
- Increased numbers in parasitic infection, allergies, spleen and CNS disease
- Phagocytosis of antigen-antibody complex and allergens
- Release of enzymes to destroy parasites
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Basophils
- S-shaped nucleus (often obscured by granules)
- Large granules
- Increased numbers in chicken pox, sinus infection, and diabetes
- Secrete histamine (vasodilator)
- Secrete heparin (anticoagulant)
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Lymphocytes
- Dark, large nucleus
- Variable amounts of cytoplasm
- Increased numbers during any infection or immune response
- Destroy cells (cancer, foreign, infected)
- Present antigens to activate other immune cells
- Coordinate immune action
- Secrete antibodies
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Types of Lumphocytes
- T Cells: attack foreign cells
- B Cells: produces antibodies that attack antigens throughout the body
- Natural Killer (NK) cells: detect and kill body's own cells that have been infected or are cancerous
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Monocytes
- Ovoid, kidney or horseshoe shaped nucleus
- Increased numbers in viral infections and inflammation
- Phagocytosis of pathogens and debris
- Attract other leukocytes
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Complete Blood Count (CBC)
A count of all the cells in the blood
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Leukopenia
- Disorder caused by low WBC count
- Increased risk of infection
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Leukemia
- Cancer of hemopoietic tissue producing extraordinarily high number of abnormal WBCs
- Impaired blood clotting; lots of infections
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Myeloid Leukemia
Uncontrolled granulocyte production
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Lymphoid Leukemia
Uncontrolled lymphocyte and monocyte production
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Acute Leukemia
Sudden onset, rapid progression, death within months
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Chronic Leukemia
Undetected for months, several year survival time
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Platelets
- Small fragments of megakaryocyte cells
- Secrete vasoconstrictors to reduce blood loss
- Stick together to form platelet plugs to seal breaks in blood vessels
- Secrete procoagulants to promote clotting
- Initiate clot-dissolving enzyme when clot is no longer needed
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Platelet Production
- Some stem cells become megakaryoblasts
- Megakaryoblasts replicate DNA/proteins without dividing
- Found in bone marrow next to blood sinusoids
- Blood flow breaks off pieces called platelets
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Hemostasis
- Cessation of bleeding (otherwise hemorrhage results)
- 3 Mechanisms: vascular spasm, platelet plug formation, blood clotting (coagulation)
- Platelets are critical
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Vascular Spasm
- Constriction of blood vessel occurring immediately after injury
- Endothelial cells release chemicals that facilitate repair process
- Endothelial cells become "sticky," the ones on either side of the injury stick together
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Platelet Plug Formation
- Platelets stick together and to broken blood vessels
- Platelets constrict to draw sides of broken vessel together
- Platelets secrete chemicals that attract more platelets (positive feedback) until vessel is sealed
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Coagulation
- Blood clots to form best protection against blood loss
- Cascade of enzymes converts fibrinogen to insoluble strands of fibrin
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Control of Clotting
- Anticoagulants inhibit clotting
- Heparin (released by basophils) helps anticoagulants
- Aspirin inhibits release of prostaglandins, which prevents platelet aggregation and clot formation
- Ca2+ and vitamin K required for clotting
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Hemophilia
- Caused by deficiency in one of the enzymes needed for clotting
- Wounds never heal, and blooding may last days
- Sometimes results in hemorrhage in brain that is fatal
- Regular injections of clotting factors used as primary treatment
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Thrombosis
An abnormal clotting of blood in intact blood vessel
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Embolus
Piece of clot that breaks off and travels through body
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Medicinal Leeches
Secrete anticoagulants as they suck blood
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