Histology of 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
• Combination of Hemoglobin with respiratory gases:

  • Oxyhemoglobin: Combination with oxygen
  • Carbaminohemoglobin: Combination with carbon dioxide
  • Carboxyhemoglobin: Combination with carbon monoxide, irreversible
• Erythrocyte cytoplasm lacks all organelles but is densely filled with hemoglobin
• Shape of erythrocyte maintained by membrane proteins:

  • Integral membrane proteins: glycophorins, band 3
  • Peripheral membrane proteins: cytoskeletal proteins including spectrin, tetramers, actin, band 4.1 protein
• Life span of erythrocytes is about 120 days
• Sickle cell disease caused by a single-point mutation in the gene encoding the β-globin chain of hemoglobin A:

  • Sickle erythrocytes are inflexible
  • Shortened life span leading to profound anemia
  • Much more viscous than normal cells
• Leukocytes (White Blood Cells)
• Granulocytes:

  • Neutrophils
  • Eosinophils
  • Basophils
• Agranulocytes:

  • Lymphocytes
  • Monocytes
• Neutrophils:

  • Constitute 60-70% of circulating leukocytes
  • Nucleus with 2-5 lobes, hypersegmented if more than 5
  • Specific granules (secondary granules) stained salmon pink, azurophilic granules (primary granules) stained deep reddish-purple
  • Short-lived cells with a half-life of 6-7 hours and a life span of 1-4 days in connective tissue
• Eosinophils:

  • About the same size as neutrophils, typically bilobed nuclei
  • Specific granules stained by eosin, contain histaminase, collagenase, cathepsins
  • Associated with allergic reactions, parasitic infections, and chronic inflammation
• Basophils:

  • Less than 1% of blood leukocytes
  • Numerous large granules in cytoplasm stain with basic dyes
  • Specific granules contain heparin, histamine, heparan sulfate, leukotrienes, IL-4, IL-13
  • Azurophilic granules are lysosomes containing lysosomal acid hydrolases
• Lymphocytes:

  • Second most numerous white cells in the blood
  • Nuclei ovoid or kidney-shaped, dense chromatin
  • Three functionally distinct types: T lymphocytes, B lymphocytes, NK cells
• Monocytes:

  • Precursors of cells of the mononuclear phagocytic system
  • Transform into macrophages, function as antigen-presenting cells
  • Oval, horseshoe-shaped, or kidney-shaped nuclei, basophilic cytoplasm with fine azurophilic granules
  • Half-life in blood is 12-100 hours, no strong evidence of recirculation after entering connective tissues
• Platelets (Thrombocytes)
• Non-nucleated, disc-like cell fragments 2-4 μm in diameter

  • Originate from fragmentation of giant polyploid megakaryocytes in bone marrow
  • Promote blood clotting and help repair minor tears or leaks in small blood vessels
  • Life span about 10 days
• Structurally divided into four zones:

  • Peripheral zone: cell membrane with glycocalyx
  • Structural zone: microtubules, actin filaments, myosin
  • Organelle zone: mitochondria, peroxisomes, glycogen particles, granules
  • Membrane zone: open canalicular system, dense tubular system
• Platelet Function:

  • Primary aggregation: platelet plug formation
  • Secondary aggregation: release of adhesive glycoprotein and ADP for further aggregation
  • Blood Coagulation: factors promote fibrin formation for clotting
  • Clot reaction: clot contracts in blood vessel lumen
  • Clot Removal: plasmin enzyme removes clot, new tissue formation restores wall
• Blood cells include erythrocytes (red blood cells), leukocytes (white blood cells), and platelets (thrombocytes)

  
• Staining methods for blood cells include Romanovsky mixed dyes, Giemsa’s, Leishman’s, and Wright’s dyes
• Erythrocytes lack organelles but are filled with hemoglobin, maintaining their shape with membrane proteins
• Anemia is a decrease in erythrocyte concentration, while erythrocytosis is an increase, often related to physiological conditions
• Erythrocytes have different sizes: macrocytes (>9 µm), microcytes (<6 µm), and anisocytosis refers to cells varying greatly in size
• Erythrocytes form reversible combinations with respiratory gases like oxyhemoglobin and carbaminohemoglobin
• Sickle cell disease results from a mutation in the gene encoding the β-globin chain of hemoglobin A, causing inflexible, viscous erythrocytes
• Neutrophils are the most common type of white blood cell, produced in the bone marrow and released into the bloodstream to fight infection

  
• Neutrophils contain granules with antimicrobial peptides and proteins, enzymes, and chemicals like histamine to kill bacteria
• Neutrophils have a short lifespan of 6-7 hours in the blood and 1-4 days in connective tissue
• Eosinophils are white blood cells associated with allergic reactions, parasitic infections, and chronic inflammation

  
• Eosinophils contain specific granules with histaminase, collagenase, and azurophilic granules with hydrolytic enzymes
• Eosinophils play a major role in host defense against helminthic parasites and are found in large numbers in allergic conditions
• Basophils are white blood cells with large granules that stain with basic dyes, containing substances like histamine and leukotrienes

  
• Basophils are less than 1% of blood leukocytes and have granules similar to mast cells
• Lymphocytes are the second most numerous white cells in the blood, increasing in response to viral infections and playing a crucial role in the immune response
• Platelets are non-nucleated, disc-like cell fragments 2-4 µm in diameter, originating from giant polyploid megakaryocytes in the bone marrow

  
• Platelets promote blood clotting and help repair minor tears or leaks in small blood vessels, preventing blood loss from the microvasculature