Blood

• Blood


  A specialized connective tissue
• Components of blood

  • Plasma
  • Erythrocytes
  • Leukocytes
  • Platelets

  
• Plasma


  • A fluid extracellular material where cells of the blood are suspended

  
• Erythrocytes, leukocytes, platelets


  • Cells circulating in the plasma

  
• Functions of blood


  • Delivery of nutrients and oxygen
  • Transport of wastes and carbon dioxide away from cells
  • Delivery of hormones and other regulatory substances to and from cells and tissues
  • Maintenance of homeostasis by acting as a buffer and participating in coagulation and thermoregulation
  • Transport of humoral agents and cells of the immune system
• Plasma


  Yellowish translucent, slightly viscous supernatant
• Buffy coat


  White or grayish thin layer between the plasma and the hematocrit consisting of leukocytes and platelets

  
• Hematocrit


  Erythrocytes make up the bottom layer and their volume
• Hematocrit is normally about 45% of the total blood volume in healthy adults
• Serum


  A yellowish liquid formed when plasma proteins react together, contains growth factors and other proteins released from platelets during clot formation

  
• Clotting in collected blood is prevented by the addition of anticoagulants (eg, heparin, citrate)
• Plasma


  An aqueous solution, pH 7.4, containing substances of low or high molecular weight that make up 8–10% of its volume
• Substances in plasma

  • Proteins
  • Nitrogenous waste products
  • Hormones
  • Electrolytes
• Plasma proteins


  Account for approximately 7% of the dissolved components
• The composition of plasma is usually an indicator of the mean composition of the extracellular fluids in tissues
• Albumin


  The most abundant plasma protein, made in the liver and serves primarily in maintaining the osmotic pressure of the blood, also acts as carrier protein
• Other major plasma proteins

  • Alpha- and Beta-globulins
  • Gamma-globulin (immunoglobulins)
  • Complement proteins
  • Fibrinogen
• Erythrocytes


  Biconcave discs that lack nuclei, packed with the O2-carrying protein hemoglobin
• Erythrocytes


  • Biconcave shape provides a large surface-to-volume ratio and facilitates gas exchange
  • Quite flexible, which permits them to adapt to the irregular bends and small diameters of capillaries, assuming a cuplike-shape
• Integral membrane proteins of erythrocytes

  Glycophorin C, Band 3 protein
• Peripheral membrane proteins of erythrocytes

  Spectrin tetramers, actin, band 4.1 protein, adducin, band 4.9 protein, and tropomyosin
• Any defect in the expression of genes that encode the different cytoskeleton proteins can result in abnormally shaped and fragile erythrocytes
• Abnormally shaped erythrocytes

  • Hereditary spherocytosis
  • Hereditary elliptocytosis
• Anemia


  Decreased number of erythrocytes in the blood
• Erythrocytosis, or polycythemia


  Increased number of erythrocytes
• Abnormal erythrocyte sizes

  • Macrocytes (>9 um)
  • Microcytes (<6 um)
• Anisocytosis


  Presence of a high percentage of erythrocytes with great variations in size
• Poikilocytosis


  Variation in erythrocyte shape
• Abnormal erythrocyte shapes


  • Oval
  • Pear-shaped
  • Teardrop-shaped
  • Saddle-shaped
  • Helmet-shaped
  • Irregularly shaped
• Oxyhemoglobin


  Hemoglobin combined with O2
• Carbaminohemoglobin


  Hemoglobin with CO2
• Combination of hemoglobin with carbon monoxide (CO) is irreversible, reducing the cells' capacity to transport O2
• Anemia


  A pathologic condition characterized by blood concentrations of hemoglobin below normal values
• Causes of anemia

  • Loss of blood (hemorrhage)
  • Insufficient production of erythrocytes by the bone marrow
  • Production of erythrocytes with insufficient hemoglobin
  • Accelerated destruction of blood cells
• Leukocytes


  White blood cells that migrate to the tissues where they become functional and perform various activities

  
• Groups of leukocytes

  • Polymorphonuclear granulocytes
  • Mononuclear agranulocytes
• Granulocytes

  Possess two types of granules: specific granules and azurophilic granules
• Contents of granulocyte granules

  • Myeloperoxidase
  • Defensins
  • Lysozyme
• Neutrophils


  60–70% of circulating leukocytes, 12–15 um in diameter in blood smears, with nuclei having two to five lobes linked by thin nuclear extensions, first leukocytes to arrive at sites of infection
• Neutrophil activation and migration


  1. Interaction of surface adhesion molecules (selectins) with endothelium

  2. Rolling on endothelial surface

  3. Adhering to endothelium and responding to chemokines