Blood Cell Types

Basophil 

• Structure
  • bilobate nucleus covered by densely staining basophilic granules
• Function
  • mediates allergic reaction
• Derived from
  • granulocyte precursors
• Pathologies
  • basophilia
    • seen with CML
• Other important features
  • basophilic granules contain
    • heparin (anticoagulant)
    • histamine (vasodilator)
    • vasoactive amines
• can synthesize leukotrienes

Platelet (thrombocyte) 

• Structure
  • smallest formed element in the blood
  • anucleate
• Function
  • primary hemostasis and blood clotting
  • prevents leakage of damaged vessels
• When activated by endothelial injury
  • aggregates with other platelets
  • interacts with fibrinogen to form hemostatic plug
• Derived from
  • small fragments of membrane/cytoplasm from megakaryocytes
• Pathologies
  • thrombocytopenia or platelet dysfunction results in petechiae, increased bleeding time
• Other important features  
  • contains
    • dense granules (ADP, calcium)
    • α-granules (vWF, fibrinogen)
  • approximately 1/3 of platelet pool is stored in spleen
    • asplenia results in thrombocytosis
  • Lifespan = 8-10 days
• important because aspirin permanently inactivates platelets and it takes this long to fully replenish functional platelets

Erythrocyte  

• Structure
  • anucleate
  • biconcave
    • gives large surface area to volume ratio
• Function
  • gas exchange (O₂ and CO₂)
    • due to large surface area
  • CO₂ transport
    • membrane contains the chloride-bicarbonate antiporter
    • important in the physiologic chloride shift
      • allows the RBC to transport CO₂ from the periphery to the lungs for elimination
• Derived from
  • reticulocyte
    • immature erythrocyte
• Pathologies
  • anisocytosis = varying sizes
  • poikilocytosis = varying shapes
• Other important features
  • glucose functions as only source of energy
  • RBCs lack mitochondria so cannot use
    • citric acid cycle
    • β-oxidation of fatty acids
    • ketone body synthesis
• survival time = 120 days 

Mast cell

• Structure
  • cells in tissue with surface bound IgE
• Function
  • mediates allergic reaction via degranulation when IgE on surface is crosslinked
    • secretory granules contain
      • histamine
      • heparin
      • eosinophil chemotactic factors
    • also contains tryptase
• Derived from
  • mast cells resemble basophils structurally and functionally and are derived from the same precursor
• Pathologies
  • type I hypersensitivity reactions
• Other important features
• cromolyn sodium prevents mast cell degranulation

Eosinophil

• Structure 
  • bilobate nucleus with large eosinophilic granules that do not cover the nucleus
• Function 
  • defends against invasive helminthic infections
    • uses major basic protein
  • phagocytoses antigen-antibody complexes
  • contains reaction following mast cell degranulation
    • produces anti-inflammatory histaminase and arylsulfatase
• Derived from
  • granulocyte precursors
• Pathologies
  • eosinophilia
    • neoplasms (e.g., Hodgkins lymphoma)
    • allergic processes
    • asthma
    • collagen vascular diseases
• invasive helminths

Neutrophil

• Structure
  • multilobed nucleus (3-5 lobes) with large spherical, azurophilic granules
• Function
  • acute inflammatory response cell
  • phagocytic
• Derived from
  • granulocyte precursor
• Pathologies
  • hypersegmented nuclei in B₁₂ and/or folate deficiencies (> 5 lobes)
• Other important features
  • granules contain
    • hydrolytic enzymes
    • lysozyme
    • myeloperoxidase
• lactoferrin

Monocyte

• Structure
  • cells in peripheral blood larger than RBCs with kidney-shaped nucleus
  • “frosted-glass” cytoplasm
• Function
  • phagocytosis
  • antigen presentation
  • differentiate into macrophages when it reaches tissue
• Derived from
  • monocytic precursor
• Pathologies
• monocytic leukemia

Macrophage

• Function
  • phagocytosis
  • antigen presentation
  • tissue healing
• Derived from
  • circulating monocytes
• Pathologies
  • chronic inflammation inflammatory may have dysregulated macrophages
  • M. tuberculosis can live inside macrophages
• Other important features
  • long life in tissues
• activated by γ-interferon

Dendritic cells

• Function
  • professional antigen-presenting cells (APCs)
  • main inducers of primary antibody response
• Other important features
• called Langerhans cells in skin

B lymphocyte

• Structure
  • circular nucleus with small amount of surrounding pale cytoplasm
• Function
  • antibody production
    • B cells differentiate into plasma cells
  • antigen presentation
• Derived from
  • lymphocytic precursor in bone marrow
  • matures in bone marrow also
• Pathologies
• B-cell lymphoma

T lymphocyte

• Structure
  • circular nucleus with small amount of surrounding pale cytoplasm
• Function
  • mediates cellular immune responses
  • T cells differentiate into
    • cytotoxic T cells (MHC I, CD8)
    • helper T cells (MHC II, CD4)
      • also helps with antibody production
    • suppressor T cells
• Derived from
  • lymphocytic precursor in bone marrow
  • matures in the thymus
• Pathologies
  • helper T cells destroyed in HIV infection
• T-cell lymphoma

Plasma cell

• Structure
  • abundant RER
  • off center nucleus with clock-face chromatin
• Function
  • produce large amounts of antibody specific to a particular antigen
• Derived from
  • B cells
• Pathologies
  • multiple myeloma