C4

• Blood is a fluid tissue that circulates through vascular channels to carry nutrients to the cells and waste products to the excretory organs
• The major function of blood is to maintain homeostasis
• The total volume of circulating blood is kept remarkably constant and is expressed relative to body weight (% or ml/kg)
• The blood volume for most mammals is approximately 7-8% of the total body weight
• The intercellular substance, plasma, comprises 45-65% of the total volume and the cellular components make up 35-55%
• Freshly drawn blood rapidly clots into a jellylike mass. If clotting is prevented, however, the blood cells settle
• Three Distinct Layers of Settled or Centrifuged Blood

  • The lowest layer consists of erythrocytes and is called packed cell volume (PCV) or hematocrit
  • The thin gray white middle layer, the buffy coat, is composed of platelets above and leukocytes below
  • The uppermost layer of centrifuged blood is plasma
• Approximately 7-10 x 10^6 erythrocytes, 8-12 x 10^3 leukocytes, and 2-4 x 10^5 platelets per mm3 are common in most large domestic animals
• Components of Blood

  • Plasma
  • Blood cells
• Plasma


  A protein-rich fluid component of the blood containing water, dissolved substances, and solids such as proteins, lipids, electrolytes, inorganic ions, hormones, pigments, vitamins, and dissolved gases
• Blood cells

  • Erythrocytes or Red Blood Cells (RBC)
  • Leukocytes or White Blood Cells (WBC)
  • Thrombocytes or Platelets
• Leukocytes

  • Agranulocytes (Lymphocytes and Monocytes)
  • Granulocytes (Neutrophils, Eosinophils, and Basophils)
• In mammalian species, the platelet is a cell fragment, not a cell like in avian species
• Characteristic Features of Blood Cells

  • ERYTHROCYTES (Red Blood Cells or Rubricytes) are the most numerous cells in the blood
  • When mature, they are in the form of nonnucleated biconcave disk and lack cytoplasmic organelles
  • Their cytoplasm contains oxygen-binding protein hemoglobin
  • Their small diameter helps to minimize their surface-to-volume ratio, facilitating oxygen exchange
  • Mature erythrocytes have a limited lifespan in the circulation before they are removed by macrophages in the spleen and bone marrow
• In isotonic solution, erythrocytes do not undergo any change. In hypotonic solution, erythrocytes swell and assume a spherical shape. Excessive swelling makes the plasma membrane incapable of retaining hemoglobin
• In isotonic solution (like plasma), erythrocytes do not undergo any change
• In hypotonic solution


  1. Erythrocytes swell and assume a spherical shape

  2. Excessive swelling makes the plasma membrane incapable of retaining hemoglobin

  3. Hemoglobin escapes into the surrounding fluid, coloring it

  4. This is known as hemolysis

  5. When hemolysis occurs, certain substances remain within the erythrocyte to leave a “shadow” or “ghost” of the cell
• In hypertonic solution

  The erythrocyte shrinks irregularly and are said to be crenated
• Average life span of erythrocyte in various domestic species

  • Canine: 120 days
  • Feline: 73 days
  • Equine: 145 days
  • Bovine: 159 days
  • Ovine: 110 days
  • Caprine: 125 days
  • Porcine: 67 days
• Depth and size of concavity of erythrocytes vary with species

  • Typical biconcave erythrocytes - in dogs, cows, and sheep
  • Shallow concavity erythrocytes - in horses and cats
  • Flat erythrocytes - in goats and pigs
• Mature erythrocytes have a central pale area surrounded by orange (hemoglobinized) cytoplasm that varies among species
• Abnormalities in RBC’s

  • Anisocytosis (variation in size)
  • Poikilocytosis (variation in shape)
  • Reticulocytes
  • Nuclear fragments
• Howell-Jolly bodies are non-refractile nuclear remnants, which are small, round, pyknotic and deeply basophilic inclusions within the erythrocytes
• Heinz bodies are erythrocyte refractile bodies, which appear as pale areas within the cytoplasm resulting from the oxidation of hemoglobin
• Rouleaux formation is a condition when erythrocytes tend to adhere to each other and form long chain resemblin
• Cytoplasmic granules found in leukocytes


  • Specific granules found only in granulocytes
  • Azurophilic granules occur in both granulocytes and agranulocytes
• Main Groups of Leukocytes

  • Agranulocytes
  • Granulocytes
• Types of agranulocytes

  • Lymphocytes
  • Mononuclear leukocytes
• Lymphocytes


  White blood cells with spherical nuclei often flattened or slightly indented on one side, densely heterochromatic, staining purplish blue to black and nearly fills the cell
• Immunological classification of lymphocytes

  • B-lymphocytes
  • T lymphocytes
• 1. lymphocytes


  • Responsible for production of antibodies (immunoglobulins) in response to antigenic stimulation
  • Basis for the blood-borne or humoral antibody immunity in the organism
  • Occur in the bone marrow, bursa of Fabricius (in birds), germinal centers of lymphatic nodules and splenic nodules
• T lymphocytes

  • Responsible for cell-mediated immunity (CMI)
  • Occur in the thymus, paracortical zones of lymphatic nodules and the periarteriolar zone or splenic corpuscles
• Small lymphocytes are the predominant lymphocytes in the circulating blood and are comparable in size to erythrocytes
• Medium lymphocytes are difficult to distinguish from monocytes
• Large lymphocytes typically occur in extravascular tissues such as lymphatic tissue
• Locations of T lymphocytes

  • Thymus
  • Paracortical zones of lymphatic nodules
  • Periarteriolar zone or splenic corpuscles
• Most of the circulating lymphocytes are T cells
• The life span of lymphocytes may vary from hours to years
• Long-lived B and T cells are believed to be memory cells
• Derivatives of lymphocytes in response to antigenic stimulation

  1. Cytotoxic (killer) T cells secrete substances that kill other cells and play a major role in graft rejection

  2. Null cells constitute 10-15% of blood lymphocytes

  3. Helper T cells enhance the activity of some B cells and other T cells

  4. Suppressor T cells inhibit the activity of some B cells and other T cells

  5. Memory cells undergo blast transformation when stimulated by an antigen and return to an inactive state retaining the capacity to respond more quickly to the next encounter

  6. Effector cells are the other daughter cells resulting from blast transformation that becomes activated to carry out an immune response to the antigen

  7. Lymphokines are low molecular weight proteins produced primarily by T cells such as Macrophage Aggregating Factor (MAP), Mitogenic Factor (MF), and Interferon