Histo lec

• Blood


  Specialized type of loose connective tissue located within blood vessels
• Contents of blood


  • Plasma (extracellular material; fluid matrix)
  • Formed elements
• Formed elements


  • Erythrocytes (red blood cells)
  • Leukocytes (white blood cells)
  • Platelets (cell fragments)

  
• Plasma


  Aqueous solution, pH 7.4, containing substances of low or high molecular weight that make up 7% of its volume
• Plasma components


  • Water (92%)
  • Proteins (7%)
  • Other solutes (1%)
• Plasma proteins


  • Albumin
  • Globulins (alpha, beta, gamma)
  • Immunoglobulins
  • Fibrinogen
  • Complement proteins
• Serum


  Plasma minus fibrinogen and clotting factors, plus growth factors released by platelets

  
• Hemopoiesis


  Production of the formed elements of blood
• Hemopoietic tissues


  • Embryonic: Yolk sac, Liver, Spleen, Bone marrow
  • Adult: Myeloid tissue (bone marrow), Lymphoid tissue (bone marrow, thymus, lymph nodes, spleen, MALT)

  
• Normal number of formed elements in blood
• Normal WBC differential count
• Normal lifespan of formed elements
• Erythrocytes (red blood cells)


  • Flexible, biconcave discs, lack nuclei and organelles, filled with hemoglobin, carry oxygen and carbon dioxide, maintain shape through peripheral proteins

  
• Erythropoiesis


  Production of red blood cells, stimulated by erythropoietin hormone from kidneys in response to low oxygen levels

  
• Spherocytosis


  Red blood cells become sphere-shaped rather than biconcave, due to defective spectrin, ankyrin, or band 3 proteins

  
• Hematocrit


  Erythrocyte volume, low levels lead to anemia, high levels lead to polycythemia
• Leukocytes (white blood cells)


  • Leave blood and migrate to tissues, become active and perform immune functions, die by apoptosis after function is complete, have spherical shape in blood but become amoeboid in tissues, contain cytoplasmic granules

  
• Types of cytoplasmic granules

  • Azurophilic (primary) granules
  • Specific (secondary) granules
• Granulocytes


  • Neutrophils
  • Eosinophils
  • Basophils
• Neutrophils are the first leukocytes to arrive at sites of infection

  
• Azurophilic granules


  Specialized lysosomes; found in both granulocytes and agranulocytes
• Azurophilic granules


  Binds to Azure dye (blue to purple)
• Azurophilic granules


  aka Primary granules
• Specific granules


  Smaller granules containing proteins and enzymes; found only in granulocytes
• Specific granules


  Binds to neutral, basic, and acidic dyes resulting to different colors of granules after staining
• Specific granules


  aka Secondary granules
• Granulocytes


  • Contain cytoplasmic granules
  • Have polymorphic nuclei
• Granulocytes


  Granular appearance of cytoplasm

  
• Granulocytes


  Distinguishing feature on blood smear

  
• Neutrophils


  • Neutrophils are 12-15 μm in diameter in blood smears, with nuclei having two to five lobes linked by thin nuclear extensions
  • Neutrophils are inactive and spherical while circulating but become amoeboid and highly active during diapedesis and upon adhering to ECM substrates such as collagen
  • Usually the first leukocytes to arrive at sites of infection where they actively pursue bacterial cells using chemotaxis and remove the invaders or their debris by phagocytosis

  
• Eosinophils


  • Eosinophils are far less numerous than neutrophils, constituting only 1%-4% of leukocytes
  • In blood smears, this cell is about the same size as a neutrophil or slightly larger, but with a characteristic bilobed nucleus

  
• Basophils


  • Basophils are also 12-15 μm in diameter but make up less than 1% of circulating leukocytes and are therefore difficult to find in normal blood smears
  • The nucleus is divided into two irregular lobes, but the large specific granules overlying the nucleus usually obscure its shape

  
• Agranulocytes


  • NO specific granules, but have few azurophilic granules
  • Spherical nucleus maybe indented, but not lobulated
• Lymphocytes


  • Are typically the smallest leukocytes and constitute approximately one-third of these cells
  • Mature lymphocytes can be subdivided into functional groups by distinctive surface molecules (called "cluster of differentiation" or CD markers) that can be distinguished using antibodies with immunocytochemistry or flow cytometry
  • Major classes include B lymphocytes, helper and cytotoxic T lymphocytes (CD4+ and CD8+, respectively), and natural killer (NK) cells

  
• Monocytes


  • Monocytes are precursor cells of macrophages, osteoclasts, microglia, and other cells of the mononuclear phagocyte system in connective tissue of nearly all organs
  • Circulating monocytes have diameters of 12-15 μm and have nuclei that are large and usually distinctly indented or C-shaped

  
• Platelets


  Membrane-bound cell fragments; size: 2-3 µm
• Platelets


  Produced by fragmentation of Megakaryocytes
• Platelets


  • Anucleate; but with the following organelles: Mitochondria, ribosomes, Golgi complex, smooth and rough ER
• Platelets


  Functions: Hemostasis - arrest of bleeding after injury to blood vessel (platelet plug and clot formation)
• The circulatory system pumps and directs blood cells and substances carried in blood to all tissues of the body