Histology - Blood

• Where does the maturation of erythrocytes primarily occur? bone marrow
• What is the characteristic nuclear change observed during the maturation of erythrocytes? Large, euchromatic, and transcriptionally active nucleus
• Which blood cell type shows basophilic cytoplasm with abundant rough endoplasmic reticulum (RER)? Reticulocytes
• Where do megakaryocytes produce blood platelets? Bone marrow
• Fluid extracellular Material – Plasma
• Propelled by rhythmic contraction of the heart - blood
• Average Volume (blood): 5L
• Formed Elements (ELP):

  Erythrocytes

  Leukocytes

  Platelets
• Functions of Blood


  1.Transport nutrients, oxygen, wastes, and carbon dioxide to and from the tissues.

  2. To convey hormones, cytokine, chemokines, and other soluble regulatory molecules.

  3. To transport leukocytes and antibodies through the tissues.

  4. To maintain homeostasis.
• Albumin. Serves to maintain the osmotic pressure of the blood; transport insoluble metabolites.
• Globulins (𐓟- and ß-). Transport metal ions; protein-bound lipids, lipid-soluble vitamins.
• Immunoglobulins (antibodies or y-globulins). Secreted by plasma cells; antibodies for host defense.
• Complement Proteins. Comprise a defensive system important in inflammation and destruction of microorganisms.
• Clotting Factors. Formation of blood clots.
• Plasma Lipoproteins. Transport of triglycerides and cholesterol to/from the liver.
• Erythrocytes (RBC)


  Red blood cells
• Erythrocytes


  • Life span in blood: 120 days
  • Size: ~8 um diameter, ~2 um thickest point, ~1 um thinnest point
  • Shape: Biconcave disc, maintained by a cytoskeletal complex (spectrin, actin, etc.)
  • Flexible: bend and adapt to pass through small capillaries
• LM appearance in smear(RBC)

  • Pink circle with light center, Center is thinner because of biconcave shape, No nucleus
• TEM appearance(RBC)

  • Solid dark gray cytoplasm because of highly concentrated hemoglobin
• Functions of erythrocytes

  • Transport of oxygen and carbon dioxide, bound to hemoglobin, Majority of CO2 is transported as HCO3-
  • pH homeostasis, Carbonic anhydrase: CO2 + H2O -> HCO3- + H+, Band 3 membrane proteins. Exchanges HCO3- for extracellular Cl-
• RBC at angles of capillary bifurcations: assume a cuplike shape
• RBC in larger blood vessels: adheres to one another loosely in stacks called rouleaux
• THROMBOCYTES (platelets)

  Life Span in Blood - About 10 days

  Size

  ~ 2-3 um in diameter

  Shape

  ~ biconcave disc

  ~ non nucleated

  Origin

  ~ cytoplasm of megakaryocyte in bone marrow

  LM appearance in smear

  ~ small, basophilic fragments, often appearing in clusters.

  TEM appearance

  ~ bounded by a plasma membrane

  ~ microtubules around the margin of the disk (maintains shape)

  ~ 3 types of granules, containing fibrinogen, plasminogen, thromboplastin, and other clotting factors.

  ~ membrane tubules and glycogen

  Functions

  ~ initiate blood clots
• LEUKOCYTES (WBCs)

  Granulocytes

  ~ contains azurophilic granules (lymphocytes)

  ~ Specific granules

  • Bind to neutral, basic, and acidic dyes

  ~ Polymorphic nuclei with 2 or more distinct (almost separated) lobes

  ~Terminally differentiated cells (NEB/BEN)

  • Neutrophils
  • Eosinophils
  • Basophils
• LEUKOCYTES (WBCs).

  Agranulocytes ~ contains azurophilic granules

  ~ no specific granules

  ~ nucleus is spherical/indented but not lobulated

   Monocytes

   Lymphocytes
• NEUTROPHILS (polymorphonuclear leukocyte)

  Life Span in Blood

  < 1 week

  Specific Granules

  • Type IV collagenase – aids migration
  • Lactoferrin – sequesters iron
  • Phospholipase A2 – leukotriene synthesis
  • Lysozyme – digests bacterial cell wall
• NEUTROPHILS (polymorphonuclear leukocyte)

  Non-specific Granules

  ~large, dense vesicles

  ~for killing & degrading engulfed microorganisms (LAMED)

  • Lysozyme – degrades bacterial cell wall components
  • Acid hydrolase
  • Myeloperoxidase – generates hypochlorite and other agents that are toxic to bacteria
  • Elastase
  • Defensins – small cysteine-rich proteins that bind & disrupt the cell membranes of bacteria and microorganisms.
• NEUTROPHILS (polymorphonuclear leukocyte)

  LM appearance in smear

  Size: 9-12 um in diameter

  Nucleus: multi-lobed (2-4 lobes)

  Cytoplasm:

  • Specific granules – neutrally stained
  • Non-specific granules – azurophilic
• NEUTROPHILS (polymorphonuclear leukocyte)

  TEM appearance

  Multi-lobed nucleus and numerous specific granules and lysosomes

  Functions

  ~Primarily antibacterial

  ~leave the blood flow and follow chemotactic signals to sites of wounding or other inflammation

  ~phagocytose foreign agents (bacteria)

  ~Pus – largely composed of dead neutrophils
• EOSINOPHILS

  Life Span in Blood

  < 2 weeks

  Specific Granules

  • Major Basic Protein
  • Eosinophilic cationic protein
  • Neurotoxin
  • Histaminase

  Non-specific Granules (LAME)

  ~large, dense vesicles

  ~for killing & degrading engulfed microorganisms

  • Lysozyme
  • Acid hydrolase
  • Myeloperoxidase
  • Elastase
• EOSINOPHILS


  LM appearance in smear

  Size: 10-14 um in diameter

  Nucleus: bilobed

  Cytoplasm:

  • Specific granules – pink/red color (stained w/ eosin dye)
  • Non-specific granules – azurophilic

  TEM appearance

  Specific granules are ovoid in shape, and contain a dark crystalloid body composed of major basic protein (MBP), effective against parasites. The rest of the granule contains other anti-parasitic substances.
• EOSINOPHILS

  Functions

  ~Anti-parasitic activity

  ~Mediators of inflammatory/allergic responses in tissues

  • Inactivate leukotrienes and histamine secreted by basophils
  • Engulf and sequester antigen-antibody complexes
  • Inflammatory stimulus increases production or release of eosinophils from bone marrow
  • Inflammatory suppression decreases eosinophil numbers in peripheral blood
  • Secrete PRO-inflammatory chemokine
  • Degranulates inappropriately to cause tissue damage (as in reactive airway disease)
• BASOPHILS


  Life Span in Blood

  1 – 2 years

  Specific Granules (HHEP)

  • Histamine
  • Heparin
  • Eosinophil chemotactic factor
  • Phospholipids for synthesis of leukotrienes (e.g.) slow-reacting substance for anaphylaxis SRS-A)

  Non-specific Granules (LAME)

  ~large, dense vesicles

  ~for killing & degrading engulfed microorganisms

  • Lysozyme
  • Acid hydrolase
  • Myeloperoxidase
  • Elastase
• Basophils


  Type of blood cell
• Basophils


  • Size: 8-10 um in diameter
  • Nucleus: bilobed but partially obscured by granules, which can lie over it
  • Cytoplasm: Specific granules - large, purple/black (stained w/ basic dye); not as numerous as in eosinophils
  • Cytoplasm: Non-specific granules - azurophilic
• Basophils (TEM appearance)


  • Specific granules vary in size and shape, and have occasional myelin figures (usually formed from phospholipids)
• Functions of basophils

  • Allergies & anaphylaxis (hypersensitivity reaction)
  • Binding of antigens to membrane bound IgE antibodies induces degranulation of specific granules, which lead to allergic reaction
  • In hypersensitivity reaction, widespread vasodilation (arteriolar) and vessel leakiness induce circulatory shock. Bronchial spasms cause respiratory insufficiency; combined effect is anaphylactic shock
• Basophils

  Similarity to tissue mast cells
• Monocytes

  Type of blood cell
• LYMPHOCYTES

  Life Span in Blood

  Variable (few days to several years)

  Size

  ~8 um – 15 um

  LM appearance in smear

  Cytoplasm is a narrow rim around the nucleus, and stained pale blue. T-lymphocytes and B-lymphocytes cannot be distinguished in a smear.

  TEM appearance

  The cytoplasm does not appear to be very active, containing mainly mitochondria and free ribosomes

  Functions

  ~ cellular and humoral immunity.

  • B-lymphocytes (B-cells): may differentiate into tissue plasma cells, which make antibodies. Some B-cells become memory cells.
  • T-lymphocytes (T-cells): Cytotoxic T-cells and helper T-cells