Blood - Red and White Blood Cells

Red Blood Cells

  • Hemoglobin (Hb): Protein molecule that transports respiratory gases.
    • Each RBC has 280 million Hb molecules.
    • Each Hb molecule can bind up to 4 oxygen molecules or 4 carbon dioxide molecules.
  • Hemoglobin Structure:
    • Complex quaternary structure.
    • Four globular protein subunits.
    • Each subunit has one molecule of heme.
    • Each heme contains one iron ion.
    • Easily associates/dissociates with oxygen (oxyhemoglobin, deoxyhemoglobin).
    • Iron transports oxygen.
    • Subunits can bind carbon dioxide.
  • RBC Function: Transport respiratory gases
    • In Lungs:
      • Releases carbon dioxide and binds oxygen.
      • Carries oxygen from lungs to periphery via the blood.
    • In Periphery:
      • Releases oxygen to deliver to cells.
      • Binds carbon dioxide and carries it to lungs via the blood.
  • RBC Formation and Turnover
    • 1% of circulating RBCs wear out and are replaced per day.
    • Macrophages of liver, spleen, and bone marrow recycle components.
    • Macrophages monitor circulating RBCs and engulf them before membranes rupture (hemolyze).
    • Macrophages remove Hb molecules and iron from RBCs that have ruptured (hemolyzed) in the blood stream.
  • Hemoglobin Conversion and Recycling
    • Macrophages break hemoglobin into components:
      • Globular proteins (subunits) converted to amino acids (recycled).
      • Heme converted to biliverdin (green).
      • Biliverdin converted to bilirubin (yellow).
      • Bilirubin released into the blood stream (waste).
      • Iron released into blood stream.
      • Transferrin brings iron to red bone marrow.
      • Used to make new hemoglobin (recycled).
  • Bilirubin
    • Bilirubin in the blood stream is excreted by the liver in the bile.
    • Converted to urobilins and stercobilins in the large intestine.
    • Eliminated in feces, urine.
  • Pathophysiology: Jaundice
    • Yellow skin tone.
    • Caused by bilirubin buildup.
    • Associated with immature or failing liver.
  • Pathophysiology
    • Hemoglobinuria: Hemoglobin breakdown products in urine due to excess hemolysis in bloodstream.
    • Hematuria: Whole red blood cells in urine due to kidney damage or urinary tract tissue damage.
  • Blood Cell Production
    • Erythropoiesis: RBC Production.
    • Occurs in the red bone marrow.
    • Hemocytoblasts (stem cells) divide to produce:
      • Myeloid stem cells become RBCs, platelets, all WBCs EXCEPT lymphocytes.
      • Lymphoid stem cells become lymphocytes.
  • Stages of RBC Maturation
    • Myeloid stem cell.
    • Proerythroblast (day 1).
    • Erythroblasts (3 stages; days 2-4).
    • Reticulocyte (days 5-7).
    • Mature RBC.
  • Regulation of Erythropoiesis
    • Building red blood cells requires:
      • Amino acids.
      • Iron.
      • Vitamins B12, B6, and folic acid.
    • Erythropoietin (EPO) “erythropoiesis-stimulating hormone”
      • Hormone secreted by the kidneys when oxygen in peripheral tissues is low (hypoxia).
      • Stimulates cell division in erythroblasts, increases Hb synthesis & RBC production.
      • Released during anemia, decreased blood flow to kidneys, oxygen from lungs decreases (disease or high altitude).
  • RBC Tests and Related Terminology
    • Hematocrit (Hct): Percentage of formed elements in whole blood. Normal = 37-54%. Elevated: Polycythemia. Depressed: Anemia.
    • Reticulocyte count (Retic.): Percentage of circulating reticulocytes. Normal = 0.8%. Elevated: Reticulocytosis. Depressed: Anemia.
    • Hemoglobin concentration (Hb): Concentration of hemoglobin in blood. Normal 12-18 g/dL. Elevated: Erythrocytosis/polycythemia. Depressed: Anemia.
    • RBC count: Number of RBCs per μLμL of whole blood. Normal = 4.2-6.3 million/μLμL. Elevated: Erythrocytosis/polycythemia. Depressed: Anemia.
    • Mean corpuscular volume (MCV): Average volume of single RBC. Normal = 82-101 μm3μm^3 (normocytic). Elevated: Macrocytic. Depressed: Microcytic.
    • Mean corpuscular hemoglobin concentration (MCHC): Average amount of Hb in one RBC. Normal = 27-34 pg/μLμL (normochromic). Elevated: Hyperchromic. Depressed: Hypochromic.

Blood Typing

  • Surface Antigens
    • Glycoproteins on a cell’s surface that identify cells to immune system.
    • Normal cells are ignored and foreign cells attacked.
  • Blood Types
    • Genetically determined.
    • By presence or absence of RBC surface antigens A, B, Rh.
  • Four Basic Blood Types
    • A (surface antigen A).
    • B (surface antigen B).
    • AB (antigens A and B).
    • O (neither A nor B).
    • The blood contains antibodies that will attack all basic antigen types that are NOT present on the patient’s RBC.
      • Type A blood: Type B antibodies.
      • Type B blood: Type A antibodies.
      • Type O blood: Both A and B antibodies.
      • Type AB blood: Neither A nor B antibodies.
  • Agglutinogens
    • Antigens on surface of RBCs that are screened by immune system.
    • Plasma antibodies attack and agglutinate (clump) foreign antigens.
    • Utilize agglutination to perform blood typing tests.
  • The Rh Factor
    • First found in the Rhesus monkey.
    • Either Rh positive (Rh+) or Rh negative (Rh-).
    • Rh+ means RBC have the Rh surface antigen. This blood will NEVER have Rh antibodies.
    • Rh- means RBC do not have the Rh surface antigen. This blood will ONLY have Rh antibodies after an exposure to the Rh antigen.
  • Hemolytic Disease of the Newborn: Rh- mother, Rh+ baby
    • Problems seldom develop during a first pregnancy, because very few fetal cells enter the maternal circulation then, and thus the mother’s immune system is not stimulated to produce anti-Rh antibodies.
    • Exposure to fetal red blood cell antigens generally occurs during delivery, when bleeding takes place at the placenta and uterus. Such mixing of fetal and maternal blood can stimulate the mother’s immune system to produce anti-Rh antibodies, leading to sensitization.
    • Roughly 20% of Rh– mothers who carried Rh+ children become sensitized within 6 months of delivery.
    • Because the anti-Rh antibodies are not produced in significant amounts until after delivery, a woman’s first infant is not affected.
    • In a subsequent pregnancy, the mother is sensitized to the Rh+ fetus. Therefore, the mother’s anti-Rh antibodies cross the placenta and attack the fetal red blood cells.
  • Cross-Reactions in Transfusions
    • Plasma antibody meets its specific surface antigen.
    • Blood will agglutinate (clump) and hemolyze (RBC rupture).
    • Occur if donor and recipient blood types not compatible.
    • Testing for Transfusion Compatibility.
      • Performed on donor and recipient blood for compatibility.
      • Without cross-match, type O- is universal donor.

White Blood Cells

  • White Blood Cells (WBCs) “leukocytes”
    • “White” - Do not have hemoglobin
    • Have nuclei and other organelles
    • Spherical
    • Life span: days to years
    • Most WBCs in connective tissue proper and lymphatic system organs
    • Small numbers in blood (5000 to 10,000 cells per microliter or <1% of blood volume)
  • WBC functions:
    • Defend against pathogens
    • Remove toxins and wastes
    • Attack abnormal or damaged cells
  • Four Characteristics of Circulating WBCs
    • Can migrate out of bloodstream
      • Margination:
      • Emigration:
    • Have amoeboid movement
    • Attracted to chemical stimuli (positive chemotaxis)
    • Some are phagocytic
      • Neutrophils, eosinophils, and monocytes/macrophages
  • 5 Types of WBCs
    • Neutrophils
    • Eosinophils
    • Basophils
    • Monocytes (become macrophages)
    • Lymphocytes
  • Neutrophils
    • Also called polymorphonuclear leukocytes
    • 50–70% of circulating WBCs (most abundant)
    • Pale cytoplasm granules with:
      • Lysosomal enzymes
      • Bactericides (hydrogen peroxide and superoxide)
    • Neutrophil Action
      • Very active, first to attack bacteria
      • Engulf and digest pathogens
      • Release prostaglandins and leukotrienes
      • Cause inflammation
      • Attract other cells
  • Lymphocytes
    • 20–30% of circulating WBCs (2nd most abundant)
    • NO granules, Large round nucleus
    • Migrate in and out of blood
    • Mostly in connective tissues & lymphoid organs
    • Are part of the body’s specific defense system
    • There are 3 functional classes..
    • Three functional classes of Lymphocytes
      • T cells:
        • Cell-mediated immunity
        • Attack foreign cells directly
      • B cells
        • Humoral immunity
        • Differentiate into plasma cells
        • Synthesize antibodies
      • Natural killer (NK) cells
        • Detect and destroy abnormal tissue cells (cancers)
  • Monocytes
    • 2–8% of circulating WBCs
    • Are large with kidney bean shaped nucleus
    • Enter peripheral tissues and become macrophages
    • Aggressive phagocytes that engulf large particles and pathogens
    • Secrete substances that attract immune system cells to injured area
  • Eosinophils (Acidophils)
    • 2–4% of circulating WBCs
    • Stain with red dye (called eosin), bilobed nucleus
    • Attack large parasites
    • Can phagocytize antibody marked bacteria
    • Primarily excrete toxic compounds
      • Nitric oxide
      • Cytotoxic enzymes
    • Are sensitive to allergens
    • Control inflammation with enzymes that counteract inflammatory effects of neutrophils, basophils and mast cells
  • Basophils
    • Are less than 1% of circulating WBCs (relatively rare)
    • Numerous blue stained granules
    • Accumulate in damaged tissue where they release granules into interstitial fluid
      • Histamine: Dilates blood vessels, inflammation
      • Heparin: Prevents blood clotting
  • The Differential Count and Changes in WBC Profiles
    • Differential count gives the number of each type of WBC in a sample of 100 WBC
    • Used to detect changes in WBC populations
    • Gives information about the presence of infections, inflammation, and allergic reactions
  • WBC Disorders
    • Leukopenia
      • Abnormally low WBC count
      • Occurs during chemotherapy
    • Leukocytosis
      • Abnormally high WBC count
      • Indicates infection
    • Leukemia
      • Extremely high WBC count