Hematopoietic System PDF

# The Hematopoietic System ## Introduction The hematopoietic system is a complex system responsible for the production and regulation of blood cells. This document will discuss the different compartments of blood, the processes of cell production, and the techniques used to measure blood volume....

# The Hematopoietic System ## Introduction The hematopoietic system is a complex system responsible for the production and regulation of blood cells. This document will discuss the different compartments of blood, the processes of cell production, and the techniques used to measure blood volume. ## Hematologic Studies - **Circulating blood** consists of two compartments: - **Plasma:** A watery fluid containing ions and organic molecules such as sodium, potassium, chloride, bicarbonate, and sugar. It also contains proteins like albumin, immunoglobulins, transport proteins, and clotting elements. - **Cellular compartment:** This compartment contains various types of blood cells, including red blood cells (erythrocytes), white blood cells (leukocytes), and platelets. ## Red Blood Cells (Erythrocytes) - **Production:** Red blood cells are produced from bone marrow stem cells, which go through a series of maturation stages until they become mature red blood cells. - **Function:** Primarily to transport oxygen to the body's tissues and carry carbon dioxide back to the lungs. - **Normal lifespan:** 120 days. - **Regulation:** The production of red blood cells is regulated by tissue oxygenation. Tissue hypoxia stimulates the production of erythropoietin from the kidneys, which in turn stimulates bone marrow red cell production. ## Other Cellular Components - **Leukocytes:** A major defense system within the body, divided into granulocytes, lymphocytes, and monocytes. - **Platelets:** Involved in blood coagulation, clot retraction, and maintaining the integrity of blood vessel walls. ### Hematocrit Determination A standard laboratory test used to determine the proportion of red blood cells in a sample of blood involves centrifuging anticoagulated blood in a capillary tube. The **hematocrit** is defined as the volume of packed red cells expressed as a percentage of the total volume. When hematocrit is performed on normal blood, the packed cells are arranged in three layers: - Red cells are packed at the bottom. - A layer of white blood cells is located just above the packed red cells. - A thin cream-colored layer, representing platelets, is located just above the white blood cell layer. ## Total Blood Volume Determination - **Isotope dilution principle:** Used to determine the total red cell volume (TRCV) and total plasma volume (TPV) using radiolabeled blood components. - **Calculations:** - TBV (total blood volume) = (injected dose x dilution factor)/(net whole blood sample count) - TRCV (total red cell volume) = (injected dose x dilution factor)/(net whole blood sample count) x decimal hematocrit - **Importance:** Clinically useful in diagnosing and managing polycythemia, and when hematocrit changes fail to accurately reflect changes in TRCV or TPV. ## Red Cell Survival - **Technique:** Uses "Cr-labeled autologous red cells in patients with hemolytic anemia. - **Purpose:** To determine the mean survival time of red blood cells. ## Splenic Sequestration A procedure to determine if the spleen is the site of red cell destruction in patients with increased red cell destruction. The test involves counting the labeled "Cr-red blood cells in specific anatomical locations (liver, spleen, and precordium) over time. ## Vitamin B12 Absorption Test - **Purpose:** To evaluate the absorption of vitamin B12, useful for diagnosing vitamin B12 deficiency. - **Stages:** Two stages: - **Stage I:** Evaluates the absorption of vitamin B12 without administering intrinsic factor. - **Stage II:** Evaluates the absorption of vitamin B12 with the administration of intrinsic factor. - **Procedure:** - Patient receives an oral dose of "Co-labeled vitamin B12. - The patient is given a "flushing dose" of nonradioactive vitamin B12 intramuscularly. - Two 24-hour urine collections are obtained and counted. - The percentage of administered dose excreted is calculated for each sample. ## References & Further Reading - Drew HH, Scheffel U, McIntyre PA, 2004. Hematopoietic system. In: Christian PE, Bernier DR, Langan JK, eds. Nuclear Medicine and PET Technology and Techniques, 5th ed. St. Louis, MO: Mosby, 520-535. - Fudenberg H, Baldini M, Mahoney JP, Dameshek W, 1961. The body hematocrit/venous hematocrit ratio and the splenic reservoir. Blood. 17:71-73. - Haurani FI, Sherwood N, Goldstein F, 1964. Intestinal malabsorption of vitamin B12 in pernicious anemia. Metabolism 13:1342-1348. - Huff RL, Feller DD, 1956. Relation of circulating red cell volume to body density and obesity. J Clin Invest. 35:1-4. - International Committee for Standardization in Hematology, 1973. Standard techniques for the measurement of red cell and plasma volume. Br J Harmatol 17:71-73. - International Committee for Standardization in Hematology, 1981. Recommended methods for the measurement of vitamin B12 absorption. J Nucl Med 22:1091-1093. - International Committee for Standardization in Hematology, 1971. Recommended methods for radioisotope red cell survival studies. Br J Harmatol. 21:241-250. - McDonald JW, Barr RM, Barton WB, 1975. Spurious Schilling test results obtained with intrinsic factor enclosed in capsules. Ann Intern Med. 83:827-829. - McIntyre P. 1972. Radioactive tracers in hematologic disease: 1. Hosp Pract. 7:94-108. - McIntyre P, 1975. Use of radioisotope techniques in the clinical evaluation of patients with megaloblastic anemia. Semin Nucl Med. 5:79-94. - Wright RR, T'no M, Pollycove M, 1975. Blood volume. Semin Nucl Med. 5:63-77.