HSTOLOGY (BLOOD)

• Functions of blood


  • Carrier of gases, nutrients, and waste products
  • Clot formation
  • Transport of processed molecules
  • Protection against foreign substances
  • Transport of regulatory molecules
  • Maintenance of body temperature
  • pH and osmosis regulation
• Components of blood


  • Physical characteristics and volume
  • Plasma
  • Cells of the blood

  
• Color of blood


  Varies from scarlet (oxygen-rich) to dull red (oxygen-poor)

  
• Weight of blood

  Heavier than water and about five times thicker, or more viscous, largely because of its formed elements
• pH of blood


  Slightly alkaline, with a pH between 7.35 and 7.45
• Temperature of blood

  38 degrees Celsius, or 100.4 degrees Fahrenheit, slightly higher than body temperature
• Plasma


  Transparent, yellowish fluid that contains numerous dissolved substances
• Composition of plasma

  • 90% Water
  • 10% organic compounds mainly proteins, inorganic salts, and ions
• Albumin


  Smallest but most abundant plasma protein, maintains the colloid osmotic pressure of blood, binds and transports some molecules
• Globulins

  Alpha (α) and Beta (β)- Transport metal ions, protein bound lipids, lipid-soluble vitamins, Gamma (γ)- Antibodies for host defense
• Complement system


  Consists of more than 20 proteins that are involved in the inflammatory and immune response, destruction of microorganisms
• Clotting factors


  Fibrinogen is the precursor of FIBRIN - protein needed to complete the final step of blood clotting
• Plasma lipoproteins


  Plasma proteins that transport lipid, which are insoluble in water, from the intestine to liver and from the liver to the tissues
• Cells of the blood

  • Erythrocytes (red blood cells, RBS)
  • Platelets (thrombocytes)
  • Leukocytes (white blood cells, WBC)
  • Granulocytes (with specific granules)
  • Nuetrophil (~60% of WBC)
  • Eosinophil (~4% of WBC)
  • Basophil (<1% of WBC)
  • Agranulocytes (without specific granules)
  • Lymphocyte (B-cell, T-cell) (~27% of WBC)
  • Monocyte (`8% of WBC)

  
• Erythrocyte (red blood cell, RBC)


  Life span in blood: About 120 days, Biconcave disk, 8 µm diameter, 2 µm at thickest point, 1 µm at thinnest, Flexible to pass through small capillaries, No nucleus, Highly concentrated hemoglobin, Function: Transport of oxygen and carbon dioxide
• Erythropoiesis


  1. Process of erythrocyte maturation

  2. Erythropoietin (EPO) stimulates mRNA for protein component of hemoglobin and is essential for erythrocyte production

  3. Cell and nuclear volume decreases

  4. Chromatin density intensifies until nucleus appears pyknotic and extruded from cell

  5. Decrease number of polyribosomes thus decrease basophilia

  6. Increase in hemoglobin amount

  7. Disappearance of other cell organelles

  
• Reticulocyte


  No nucleus, few polyribosomes can be seen when stained with blue cresyl blue
• Platelets (thrombocytes)


  Life span: about 10 days, 2-3 µm in diameter, Non-nucleated cell fragments derived from cytoplasm of a very large cell, the megakaryocyte, in bone marrow, Function: Platelets initiate blood clots (stop bleeding)

  
• Thrombocyte differentiation

  Platelets are fragments of megakaryocytes, Thrombopoietin (TPO) is the principal physiologic regulator of platelet production
• Leukocytes (white blood cells, WBC)

  On average, there are 4,500 to 10,500 WBC/mm3, and they account for less than 1 percent of total body volume

  
• Granulopoiesis


  1. Process of granulocyte maturation

  2. Synthesis of azurophilic granules containing lysosomal hydrolases

  3. Synthesis of specific granules that differentiate the three types of granulocyte
• Neutrophil (polymorphonuclear leukocyte)


  Life span: < 1 week, Granulocyte with specific and non-specific granules, Specific granules contain enzymes like type IV collagenase, lactoferrin, phospholipase A2, Non-specific granules (lysosomes) contain lysozyme, acid hydrolase, myeloperoxidase, elastase, Function: Primarily antibacterial

  
• Neutrophils are about 9-12 µm in diameter, larger than RBCs, with a long multi-lobed nucleus and small neutrally stained specific granules and azurophilic non-specific granules
• Eosinophil


  Life span: < 2 weeks, Granulocyte with specific granules that stain with acidic dyes
• Granulocytes


  • Lysozyme
  • Acid hydrolase
  • Myeloperoxidase
  • Elastase
• Neutrophil in blood smear

  • About 9-12 µm in diameter (larger than RBC)
  • Nucleus long and multi-lobed (usually 2-4 lobes)
  • Cytoplasm has small, neutrally stained specific granules
  • Non-specific granules are azurophilic

  
• Neutrophil function

  Primarily antibacterial
• Eosinophil in blood smear

  • About 10-14 µm in diameter
  • Bi-lobed nucleus
  • Cytoplasm has prominent pink/red specific granules (stained with eosin dye)
  • If smear not stained properly, granules may be brownish

  
• Eosinophil function


  • Anti-parasitic activity
  • Mediators of inflammatory/allergic responses in tissues
• Basophil in blood smear


  • About 8-10 µm in diameter
  • Cytoplasm contains large, purple/black specific granules (stained with basic dye)
  • Nucleus usually bilobed, but partially obscured by granules

  
• Basophil function


  Allergies and anaphylaxis (hypersensitivity reaction)
• Basophil specific granules


  • Histamine
  • Heparin
  • Eosinophil chemotactic factor
  • Phospholipids for synthesis of leukotrienes
• Basophil non-specific granules


  • Lysozyme
  • Acid hydrolase
  • Myeloperoxidase
  • Elastase
• Monocyte


  Life span: few days in blood, several months in connective tissue
• Monocyte in blood smear

  • About 16 µm, largest leukocyte
  • Large, eccentric nucleus either oval, kidney-shaped or horseshoe-shaped
  • Pale cytoplasm, often grayish, may contain occasional stained granules (lysosomes = azurophilic granules)

  
• Monocyte function

  • Migrate into tissues and constitute mononuclear phagocyte system that help destroy foreign bodies and maintain or remodel tissues
  • Mediate inflammatory response
• Tissue macrophages


  • Kupfer cells (liver)
  • Osteoclasts (bone)
  • Dust cells (lungs)
  • Microglia(brain)

  
• Antigen presenting cells


  • Dendritic Cells
  • Langerhans cells
• Lymphocyte


  Life Span: variable (few days to several years)
• Small lymphocyte in blood smear

  • About 8 µm in diameter
  • Round, dense nucleus (abundant heterochromatin)
  • Narrow rim of pale blue cytoplasm around nucleus