histo

• 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
• Plasma vs Serum


  Plasma: water and dissolved substances

  Serum: plasma minus fibrinogen and clotting factors, plus growth factors
• 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 the kidneys in response to low oxygen levels
• Spherocytosis


  Red blood cells become sphere-shaped rather than biconcave due to defective spectrin, ankyrin, 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
• Types of leukocyte granules

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


  • Contain cytoplasmic granules, have polymorphic nuclei
• Neutrophils


  12-15 μm in diameter, have 2-5 lobed nuclei, 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