Hematology exam 1

• Platelet is a discoid structure with a diameter of 1-3μm
• Platelet appears light blue to purple in color and is very granular
• Platelet consists of two parts:

  • The chromomere, which is granular and located centrally
  • The hyalomere, which surrounds the chromomere and appears agranular, clear to light blue in color
• Platelet membrane most probably comes from the plasma membrane of the megakaryocyte
• Platelets in circulation appear discoid in shape and are inactive
• Platelet membrane and glycocalyx are relatively smooth and contain porelike indentations that open communication channels into the platelet cytoplasm
• Glycoproteins incorporated in the outer layer of the platelet membrane (I, II, III, IV, V and IX) play important roles in platelet adhesion and aggregation
• Platelet membrane contains a contractile protein (thrombosthenin) which helps to maintain the platelet shape and may be responsible for changes in platelet shape
• Phospholipid constituents and other fatty acid pools required for fatty acid metabolism are located within the platelet membrane
• Platelets are cytoplasmic fragments of giant cells called megakaryocytes
• Megakaryocytes have a large nucleus
• Megakaryocytic cells can undergo multiple mitotic divisions without cytoplasmic division
• This process generates giant multinucleated or polyploid cells
• The multiple nuclei usually remain attached to each other and are often superimposed, giving a multilobulated appearance
• This results in a multiple number of chromosomes, exceeding the original two sets of chromosomes (2n)
• Endomitosis or endoreduplication is the type of division involved in this process
• Megakaryoblast:

  • Earliest recognizable stage of maturation
  • Large cell (15-50 μm in diameter)
  • Irregularly shaped with a single nucleus or several round/oval nuclei
  • Blue, non-granular cytoplasm
  • May have blunt bluish pseudopods or protrusions from the cytoplasmic membrane
• Promegakaryocyte:

  • Differs from megakaryoblast with bluish granules in cytoplasm near nucleus
  • Nucleus has divided one or more times
  • Increased in size (20-80 μm in diameter)
  • Cytoplasm rich in RNA which is basophilic
  • With maturation, cytoplasmic basophilia fades and fills with reddish-purple granules
• Mature megakaryocyte:

  • Huge cell (~150 μm in diameter)
  • Segmented nucleus with dense nuclear chromatin
  • Pinkish cytoplasm, highly granular
  • Abundant with irregular peripheral border
• Platelet production:

  • Platelets produced directly from megakaryocyte cytoplasm
  • Megakaryocyte puts out pseudopods into BM sinusoids, detach, and fragment into platelets
  • Entire megakaryocyte cytoplasm breaks away, leaving naked nucleus in BM
  • Each megakaryocyte produces between 2000-4000 platelets
  • Thrombopoietin stimulates platelet production
• Platelet life span:

  • Once released into peripheral blood, platelet has a life span of 9-11 days
  • ~30% of platelets are trapped in the spleen
  • Platelet constituents: mitochondria, glycogen deposits, alpha granules, electron dense granules, lysosomes
• Hemostasis:

  • Process to control and stop bleeding from an injured blood vessel
  • Involves blood vessels, platelets, and coagulation factors
  • Occurs in primary and secondary phases
  • Primary hemostasis involves vascular and platelet response to vessel injury
  • Secondary hemostasis involves coagulation process
  • Leads to formation of stable fibrin-platelet plug at site of injury
• Basic events in primary and secondary hemostasis after vessel injury:

  • Vasoconstriction: damaged blood vessel constricts to decrease blood flow
  • Platelet adhesion to exposed subendothelial connective tissue
  • Platelet activation and change in shape
  • Biochemical reactions leading to release reaction
  • Aspirin inhibits platelet activation by reducing production of thromboxane A2
• Blood is composed of two major constituents:

  • A liquid part called plasma
  • A solid (cellular) part
• In a normal person, approximately 55-60% of the blood is plasma, of which around 90% is water
• The remaining 10% of plasma is composed of:

  • Proteins (albumin, globulin, and fibrinogen)
  • Carbohydrates
  • Lipids
  • Vitamins
  • Hormones
  • Enzymes
  • Inorganic salts (Na, K, Ca, Mg, Cl, bicarbonate, and phosphate)
• When coagulation is prevented by anticoagulants, the liquid portion of the blood is termed plasma and contains the protein fibrinogen
• Anticoagulants commonly used for hematologic procedures are:

  • EDTA (chelates Ca++)
  • Citrate (chelates Ca++)
  • Heparin (acts by neutralizing thrombin, preventing the formation of fibrin from fibrinogen)
• If a blood specimen is allowed to clot, the liquid portion released from the clot is called serum and does not contain fibrinogen
• The cellular part of blood constitutes 40-45% and consists of three major components:

  • Red blood cells (erythrocytes)
  • White blood cells (leukocytes)
  • Platelets
• Red blood cells are non-nucleated, deeply pigmented elements primarily involved in tissue respiration and transport of O2 and CO2
• White blood cells are nucleated cells with the major function of protecting the host from the external environment
• Five distinct types of white blood cells constitute normal blood:

  • Neutrophils
  • Lymphocytes
  • Monocytes
  • Eosinophils
  • Basophils
• Platelets are cytoplasmic fragments of giant cells called megakaryocytes, involved in blood clotting
• Blood specimens for hematologic tests can be obtained by venipuncture or skin puncture, with venous blood preferred for most tests
• To examine blood cells, staining is necessary:

  • Vital or Supravital stains can be used on living cells
  • Regular stains are used on killed cells after fixing with fixatives
  • Special stains are used to stain specific structures in the cell
• Known fixatives used in Hematology include:

  • Methanol
  • Ethanol
  • Formalin
  • Glacial Acetic Acid
• Romanowsky stains are commonly used for coloring cells, consisting of:

  • A basic dye (methylene blue - blue)
  • An acidic dye (eosin - red)
  • Intermediate stains (methylene azures) for different shades
• Standard Romanowsky stains include:

  • Leishman stain
  • Jenner stain
  • May-Grun Wald stain
  • Wright stain
  • Giemsa
• The Wright stain gives excellent details of the cytoplasm and granules, while the Giemsa stain is excellent for nuclear detail