Chapter 13: Alterations in Oxygen Transport

RBCs

  • What are the functions of RBCs?
    • Transport oxygen to tissues
    • Remove carbon dioxide from the tissues
    • Buffer blood pH since they contain carbonic anhydrase
  • How are RBCs produced?
    • Through hematopoiesis: a two-stage process involving…
    • Mitotic division (proliferation)
    • Maturation (differentiation)
  • What is the role of erythropoietin?
    • Hormone from kidney that stimulates erythrocyte production
  • Where does RBC destruction occur?
    • 80-90% of RBCs get digested by macrophages in spleen and liver
    • 10-20% of RBCs are destructed inside blood vessels
  • What is the mechanism for RBC destruction?
    • As RBCs age, enzyme activities decrease and amount of membrane lipids decrease
    • The cell loses its ability to deform and becomes fragile
    • HbA levels increase
    • Heme is reduced to bilirubin
    • Globin and iron portions are conserved and reused
    • Bilirubin is then degraded to the urobilinogen and excreted primarily in the feces and urine
  • What is the product of RBC destruction?
    • Bilirubin

RBC Disorders

  • What are the basic etiologic classifications for anemia?
    • Under production of RBC
    • Overproduction of RBC (hemolysis)
    • Blood loss

Aplastic Anemia

  • What is aplastic anemia?
    • Stem cell disorder characterized by reduction of hematopoietic tissue, fatty marrow replacement
  • What is the pathogenesis of aplastic anemia?
    • Caused by toxic, radiant, or immunological injury to the bone marrow stem cells
  • What is pancytopenia?
    • Low RBC, WBC, and platelets

What are the laboratory features of aplastic anemia?

  • Pancytopenia
  • Low WBC is important for prognosis (low leukocytes = susceptibility

Pernicious Anemia

  • Folate deficiencies are associated with neural tube defects
  • Pernicious anemia is characterized by the lack of intrinsic factor, resulting in the inability to absorb vitamin B12, which plays a role in RBC formation
  • What are the laboratory features of pernicious anemia?
    • Pancytopenia with increased molecular corpuscular volume (MCV); megaloblastic dysplasia
    • Macrocytic and hypersegmented neutrophils

Anemia due to Renal Failure

  • What is the etiology of anemia due to renal failure?
    • Primarily from failure of the renal endocrine function, with causes impaired erythropoietin (EPO) production
    • Secondarily from failure of renal excretory function
  • Anemia due to renal failure leads to hemolysis, bone marrow cell depression, and blood loss
  • What are the laboratory features and clinical manifestations of anemia due to renal failure?
    • Low RBC, hematocrit, and hemoglobin
    • Some grossly deformed RBC
    • General signs and symptoms of anemia usually manifest when hematocrit decreases to <20%

Iron Deficiency Anemia

  • Iron deficiency anemia is the most common form of anemia and results in the unavailability of iron for hemoglobin synthesis
  • What are the laboratory features of iron deficiency anemia?
    • Smaller and paler RBCs
    • Low RBC indices: MCV, MCH, MCHC
    • Decreased serum ferritin

Thalassemia

  • Thalassemia is an inherited blood disorder caused by increased RBC destruction (hemolysis), resulting in decreased RBC survival rates
  • Thalassemia is associated with mutant genes that suppress the rate of globin chain synthesis
  • Thalassemia is classified by the polypeptide chains with deficient synthesis
  • Thalassemia major is the most clinically severe and homozygous
  • Thalassemia minor is less severe and heterozygous
  • What are the laboratory features of thalassemia?
    • Hypochromic, microcytic RBCs
    • MCV, MCH, and MCHC are low
    • Erythroblastic hyperplasia (bone marrow)

Sickle Cell Anemia

  • Sickle cell anemia is characterized by a genetically determined defect of hemoglobin synthesis, resulting in hemoglobin instability and insolubility
  • Sickle cell anemia is found in hemoglobin S, in which a single amino acid substitution causes the structural abnormality
  • Sickled cells cause vascular occlusion
  • What are the laboratory features of sickle cell anemia?
    • Sickled RBCs present in blood smear

Polycythemia

  • Polycythemia is characterized by excess RBCs, which results in increased blood viscosity, leading to clinical symptoms, such as hypertension
  • Primary polycythemia is characterized by
    • An absolute increase in RBC mass, leukocytosis, and thrombocytosis
    • Increased uric acid because of excess proliferation
    • Oxygen saturation is normal
  • The signs and symptoms of increased viscosity of blood are:
    • Hypertension
    • Thrombosis
    • Congested spleen and liver
  • Secondary polycythemia is characterized by increased RBC production WITHOUT an increase in WBCs or platelets