Week 15: Hematologic system review

• Blood composition


  • Plasma (protein and inorganic materials)
  • Buffy coat (platelets, leukocytes)
  • Formed elements (Erythrocytes)
• Blood volume in adults is 5-6 liters (5.5 liters on average)
• Plasma proteins


  Formed mainly in the liver
• Plasma proteins


  • Albumin (60% of total plasma protein)
  • Globulins (second most abundant protein in plasma)
  • Fibrinogen
  • Prothrombin
  • Antibodies
• Plasma


  Aqueous liquid containing organic and inorganic elements
• Hematopoiesis


  Blood cell production, constantly occurring in bone marrow after birth (medullary hematopoiesis)
• Blood cell production in tissues other than the bone marrow (extramedullary hematopoiesis) is usually a sign of disease
• Active bone marrow in adults


  • Pelvic bones
  • Vertebrae
  • Cranium and mandible
  • Sternum and ribs
  • Humerus
  • Femur
• Erythropoiesis


  Formation of red blood cells, occurs in bone marrow stimulated by erythropoietin released by kidney in response to low oxygen tension
• Reticulocyte


  • Immature red blood cell (normally 1% of RBCs), increased numbers indicate increased RBC production
  • Life span is ~120 days
  • Destruction in liver and spleen
• Intrinsic factor


  Released from parietal cells in stomach, required for vitamin B12 absorption from small intestine
• Folate


  Folic acid - water-soluble B9 vitamin required for DNA and RNA synthesis and repair and production of RBCs, stored in liver
• Lack of intrinsic factor impairs vitamin B12 absorption, risk for pernicious anemia
• Folate deficiency is more common than vitamin B12 deficiency
• Folate supplements are prescribed for pregnant women as they can protect against neural tube defects
• Regulation of erythropoiesis


  Decreased arterial oxygen levels (tissue hypoxia) stimulate release of erythropoietin from the kidney
• Hemoglobin


  Oxygen-carrying protein in the mature red cell, consists of two pairs of polypeptide chains (globins) with an attached heme molecule containing iron
• Oxyhemoglobin fully saturated has 4 oxygen molecules
• Adult hemoglobin


  Two alpha chains and two beta chains (globins), four colorful complexes of heme (iron plus protoporphyrin)
• Normal destruction of erythrocytes


  • Aged red cells are sequestered and destroyed by macrophages primarily in the spleen (liver takes over if spleen is absent)
  • Porphyrin is reduced to bilirubin, which is transported to the liver and secreted in the bile
  • Unconjugated bilirubin is not water soluble, conjugated bilirubin is water soluble
• Hyperbilirubinemia can happen with increased hemolysis, leading to jaundice
• Leukocytes


  • Hematopoietic stem cells
  • Common lymphoid progenitors
  • Common myeloid progenitors
  • B lymphocytes
  • T lymphocytes
  • NK cells
  • Neutrophils
  • Monocytes
  • Basophils
  • Eosinophils
  • Megakaryocytes
• Platelets (thrombocytes)


  Derived from stem cells and progenitor cells that differentiate into megakaryocytes, lack a nucleus, life span of 10 days, destroyed in the spleen
• Thrombopoietin (TPO)


  Produced in the liver, is the main regulator of circulating platelet numbers
• Hemostasis


  Arrest of bleeding, includes vasoconstriction, formation of a platelet plug, activation of the clotting cascade, formation of a blood clot, and clot retraction and dissolution
• Hemostasis


  1. Vasoconstriction (vasospasm)

  2. Formation of a platelet plug

  3. Activation of the clotting cascade

  4. Formation of a blood clot

  5. Clot retraction and clot dissolution
• Platelet activation

  • Adhesion to site of injury, activation which recruits more platelets to site ending with aggregation and platelet plug
  • Tissue factor released from injured tissue initiates activation of clotting cascade ending in fibrin network covering platelet plug
• Coagulation


  Blood cells are trapped in the fibrin network leading to a blood clot
• Natural anticoagulants


  Antithrombin III, Proteins C and S, and Tissue factor pathway inhibitor
• Fibrinolytic system


  Dissolution of the clot begins shortly after the formation, plasmin dissolves the clot and allows for blood flow and tissue repair
• Tissue-type plasminogen activator (tPA)


  Activates the fibrinolytic system
• Warfarin


  Anticoagulant that decreases prothrombin and other procoagulants by altering vitamin K
• Heparin


  Naturally formed and released by mast cells, binds antithrombin III and increases the ability to inactivate thrombin, factor Xa, and other clotting factors
• Prothrombin time (PT)


  Assesses function of the extrinsic pathway
• Partial thromboplastin time (PTT)


  Assesses function of the intrinsic pathway
• The spleen is the largest lymphoid organ, located on the left side of the abdomen.
• Lymphocytes are produced by bone marrow stem cells and mature into T-cells or B-cells.
• T-cells function as cytotoxic cells that destroy infected cells and cancerous cells.
• The spleen also stores platelets and produces antibodies against certain types of bacteria.
• Bone marrow produces red blood cells, white blood cells, and platelets.