lecture 6

• Circulatory System


  The system that circulates blood and lymph through the body
• Hematopoiesis


  The formation of blood cellular components
• Blood


  A (liquid) tissue circulating the entire body with different and many functions:
• Erythrocyte


  Red blood cells - biconcave, highly flexible, non-nucleated discs with a life span of ~120 days. Normal count is 4.2 - 6.2 million cells/mm3. Contains hemoglobin (globin, heme group, AA chains, Fe+2). Production is stimulated by erythropoietin (stimulus: hypoxia). Affected by: iron levels, amino acids, vitamin B12, B6, and folic acid.
• Leukocytes


  White blood cells - 1% of blood volume (4,500 - 10,500 cells /mm3). Includes neutrophils (50%-60%, phagocytic, first responder), lymphocytes (30%-40%, immune function), monocytes (can become macrophages), eosinophils (increased in allergies and parasitic infections), and basophils (become mast cells to release histamine during allergies).
• Thrombocytes


  Platelets - very small, irregularly shaped, non-nucleated fragments from megakaryocytes. Function: blood-clotting (coagulation) and hemostasis - stick to damaged tissue as well as to each other to form a platelet plug that seals small breaks in blood vessels, or they can adhere to rough surfaces and foreign materials.
• Diagnostic Tests in Hematology

  • Complete blood count (CBC) with peripheral blood smear
  • Reticulocyte count: to assess BM function
  • Clotting studies - prothrombin time, activated partial thromboplastin time, bleeding time, clotting time
  • Bone marrow smear with histochemical stains
  • Chemical analysis - serum iron, vitamin B12, folic acid, cholesterol, urea, glucose, bilirubin
• Anemia


  Reduced O2 transport in the blood due to: decrease in hemoglobin content, deficiency of a required nutrient, bone marrow function is impaired, blood loss/excessive destruction of erythrocytes occurs. Classification according to cell characteristics (morphology) or etiology. Leads to: less energy in cells, compensation mechanisms, decreased regeneration of epithelial cells, and poor perfusion in some organs.
• Iron Deficiency Anemia (IDA)

  There is insufficient iron which impedes the synthesis of hemoglobin, thereby reducing the amount of oxygen transported in the blood. RBCs are small (microcytic) and have less color (hypochromic). Causes: low iron content, chronic blood loss, impaired absorption (malabsorption), liver disease, and infections or malignancies. Diagnostic tests: CBC (Hct, MCV, MCHC), serum ferritin, serum iron, TIBC, peripheral blood smear, reticulocyte count.
• Pernicious Anemia


  Caused by the malabsorption of vitamin B12 owing to a lack of intrinsic factor, low level or absence of acid in the gastric secretion (achlorhydria). RBCs appear big (megaloblasts or macrocyte) due to impaired maturation owing to interference with DNA synthesis. Diagnostic test: CBC with PBS, reticulocyte count, vitamin B12 test (Schilling test), gastric biopsy.
• Aplastic Anemia


  Results from impairment or failure of bone marrow, leading to loss of stem cells and decreased numbers of erythrocytes, leukocytes, and platelets in the blood (pancytopenia). Etiology: idiopathic, myelotoxins (i.e., radiation, chemicals and drugs), infections (i.e., hepatitis C), autoimmune diseases (i.e., SLE), genetics. Diagnostic test: CBC, BMS.
• Hemolytic Anemia


  Results from excessive destruction of RBCs, or hemolysis, leading to a low erythrocyte count and low total hemoglobin. Causes: genetic defects affecting structure, immune reactions, changes in blood chemistry, the presence of toxins and infections, transfusion reactions and blood incompatibility in the neonate.
• Sickle Cell Anemia


  There is formation of abnormal hemoglobin, hemoglobin S (HbS) - crystallizes and changes the shape of the RBC from a disc to a crescent or "sickle" shape; cell membrane is damaged, leading to hemolysis, and the cells have a much shorter life span than normal. Etiology: sickle cell gene (HbS gene). Diagnostic test: CBC, hemoglobin electrophoresis.
• Polycythemia


  Primary polycythemia (polycythemia vera): a condition in which there is an increased production of erythrocytes and other cells in the bone marrow. Secondary polycythemia (erythrocytosis): an increase in RBCs that occurs in response to prolonged hypoxia and increased erythropoietin secretion. Increased blood volume and viscosity with blood vessels are distended and blood flow is sluggish, leading to frequent thromboses and infarctions throughout the body, especially when platelet counts are high. Etiology: unknown origin, common in 40s-60s. Diagnostic test: CBC, BME, uric acid.
• Leukemia


  Neoplasms of the leukocytes. Categories: type of cell (myeloid, lymphoid), duration (acute, chronic) mixed. One or more of the leukocyte types are present as undifferentiated, immature, nonfunctional cells that multiply uncontrollably in the bone marrow, and large quantities are released as such into the general circulation. Proliferation of leukemic cells in the bone marrow suppresses the production of other normal cells.