bloodc componentsTERI JUNGE, CST/CFA d hole blood consists of two main elements: the formed ele- ments and the liquid element. The formed elements are cell fragments and cells, known as corpuscles, which account

for approximately 45% of the total volume of the blood. The liquid element is the intracellular matrix, known as wplasma, which accounts for approximately 55% of the total volume of the blood. In the adult, hematopoiesis (blood cell production) occurs in the red bone marrow (myeloid tissue) and all types of blood cells are pro - duced from a single type of pluripotent stem cell (hemocytoblast). Addi - tionally, some leukocytes are produced by the lymphatic system.

Editor’s Note: This is part of a review series of short articles about blood. An article on blood basics was published in the January 2003 issue. The attached CE covers the first two articles in this series.

JULY 2003 The Surgical Technologist 17 232 JULY 2003 CATEGORY 1

Corpuscles red blood cells are replaced per second. Red The formed elements of blood are the erythro­ blood cells are not capable of division. cyte (red blood cell, RBC), leukocyte (white The process of erythropoiesis (red blood blood cell, WBC), and thrombocyte (platelet). cell production) is as follows:

Erythrocytes • The pluripotent stem cell is stimulated by Normal mature erythrocytes are red nonnu­ the hormone thrombopoietin (secreted cleated biconcave disks that measure approx­ by the liver) to become a blood cell (red imately 7.5 microns in diameter. The bicon­ blood cell, white blood cell—with the cave shape increases the surface area of the exception of the lymphocyte, or a platelet) cell and allows flexibility of the cell during in the myeloid tissue (myeloid progeni­ passage through the capillaries. Each red tor). blood cell consists of a cell membrane, which • The myeloid progenitor is stimulated by encloses the hemoglobin and the cytoplasm. erythropoietin to produce the megakary- Hemoglobin is the red-pigmented portion ocyte/erythroid progenitor (proerythrob­ of the erythrocyte. Each hemoglobin mole­ last), which is the differentiated stem cell ccule consists of four polypeptide chains that will eventually become the erythro­ (known as globin) and four nonprotein pig­ cyte (takes approximately 12 hours) or the ments (known as heme) that contain one fer­ thrombocyte. rous iron atom at the center. This configura­ • As the euchromatic nucleus of the proery­ tion allows four binding sites per hemoglobin throblast begins to shrink and the cyto­ molecule. Hemoglobin synthesis depends on plasm darkens with ribosomes, the the presence of iron and vitamins C, B2, B3, basophilic erythroblast is formed (takes B6, B12, E, and folate (a form of a water-sol- approximately 19 hours). uble B vitamin). Hemoglobin is responsible • The basophilic erythroblast begins to pro­ for carrying oxygen to the cells (in the form duce hemoglobin and becomes a poly­ of oxyhemoglobin) and waste products (such chromatophilic erythroblast (takes as CO2 in the form of carbaminohemoglo­ approximately 32 hours). bin) away from the cells. Antigens (agglutino­ • The polychromatophilic erythroblast gens) contained within the membrane of the becomes an orthochromatic erythroblast erythrocyte determine an individual’s blood (takes approximately 48 hours). type (ABO and Rh, positive or negative). • The reticulocyte forms as the orthochro­ Red blood cell production is triggered by matic erythroblast shed its nucleus. an oxygen sensing (negative feedback) mech­ • The reticulocyte (marrow reticulocyte) anism within the cells of the kidney. A begins to mature in the bone marrow reduced number of erythrocytes results in less (takes approximately 41 hours). oxygen being delivered to the kidney (hypox­ • The marrow reticulocyte transitions (is ia) which in turn causes the kidney cells to extruded) into the blood (blood reticulo­ release an enzyme capable of converting one cyte) where it continues to mature (takes of the plasma proteins into a hormone called approximately 32 hours). erythropoietin. Erythropoietin causes the red • The circulating mature red blood cell is bone marrow to produce more red blood functional for approximately 120 days. cells. In turn, the additional red blood cells deliver more oxygen to the kidney cells and Normal destruction of aged, abnormal, or the signal to release the enzyme is disrupted. damaged red blood cells takes place primari­ The life span of a red blood cell is 120 days; ly in the spleen and liver but can also occur in approximately 2.5 million (1% of the total) bone marrow and lymph nodes via phagocy­

The Surgical Technologist JULY 2003 18 tosis. Hemoglobin is divided into globin and oxidants (expose the cell to destruc­ heme. Globin is broken down into amino tive oxygen), lysozymes (enzymes acids that are recycled. The heme is further destructive to certain bacterial cell divided into bilirubin and iron. Iron is recy­ membranes), or defensins (antibiotic cled to the red bone marrow and bilirubin is polypeptides that are destructive to sent to the liver and is secreted in bile. The certain bacterial cell membranes). bile is excreted into the intestine where the Neutrophils develop as follows: bilirubin is converted into pigment that is expelled with the feces. • The pluripotent stem cell is stimu­ lated by the hormone thrombopoi­ Leukocytes etin (secreted by the liver) to Leukocytes are round colorless nucleated become a blood cell (red blood cell, cells that are part of the body’s defense mech­ white blood cell—with the excep­ anism. White blood cell production is called tion of the lymphocyte, or a leukopoiesis. Leukocytes are initially released platelet) in the myeloid tissue from the bone marrow into the blood stream; (myeloid progenitor). however, they do not remain in the circulat­ • The myeloid progenitor is stimulat­ ing blood. From the blood, the various cells ed by granulocyte monocyte colony escape through the capillary walls by a stimulating factor to produce the process called diapedesis. Leukocytes are granulocyte macrophage progeni­ mobile cells that migrate to the extravascular tor, which is the differentiated stem tissues using amoeboid motion. Each type of cell that will eventually become leukocyte performs a different function and either a granulocyte or a monocyte. has a different life span. Leukocytes are divid­ • The granulocyte macrophage prog­ ed into two main categories: granulocytes enitor is stimulated by granulocyte and agranulocytes. colony stimulating factor to become a neutrophil. Granulocytes The cytoplasm of the granulocyte con­ Eosinophils tains granules. Formation of granulocytes Eosinophils account for approximate­ is called granulopoiesis. There are three ly 1%-3% of all leukocytes. Eosino­ types of granular leukocytes: neutrophils, phils use phagocytosis to ingest the eosinophils, and basophils. undesirable material and destroy it by releasing its cytotoxic granules. Func­ Neutrophils tion of the eosinophil is not complete­ Neutrophils are the most common ly understood. Eosinophils are associ­ type of leukocyte accounting for ated with allergic reactions, inflamma­ approximately 54%-62% of all leuko­ tion, and the destruction of parasites cytes. Mature neutrophils are released and certain types of cancer cells. from the bone marrow into the blood. Eosinophils develop from the gran­ The neutrophils migrate from the ulocyte macrophage progenitor (refer blood to the interstitial fluid where to neutrophil development for the ini­ they await activation (due to an injury tial developmental stages) when the or infection). Neutrophils use phago­ granulocyte macrophage progenitor cytosis to ingest other cells, bacteria, that has been stimulated by granulo­ necrotic tissue, and foreign particles cyte colony stimulating factor to and then destroy them with the use of become a neutrophil is additionally

JULY 2003 The Surgical Technologist 19 influenced by interleukin-5 to become neutrophil development for the initial an eosinophil. developmental stages) when the gran­ ulocyte macrophage progenitor is Basophils stimulated by macrophage colony Basophils account for less than 1% of stimulating factor to become a mono­ all leukocytes. Basophils accumulate cyte (which eventually matures to at the site of an infection or inflamma­ become a macrophage). tion, then release their granules that contain mediators (such as heparin, Lymphocytes histamine, and serotonin), which Lymphocytes account for approxi­ increase blood flow to the area. mately 25%-38% of all leukocytes. Basophils contribute to (intensify) There are two main types of lympho­ allergic responses such as hay fever or cytes: B-lymphocytes (cells) and T- anaphylaxis related to an insect sting. lymphocytes (cells). Lymphocytes Basophils develop from the granu­ mediate the immune response. locyte macrophage progenitor (refer to Lymphocytes develop as follows: neutrophil development for the initial developmental stages) when the gran­ • The pluripotent stem cell in the ulocyte macrophage progenitor that bone marrow is stimulated by has been stimulated by granulocyte interleukin-7 to become a lym­ colony stimulating factor to become a phoid progenitor. neutrophil is additionally influenced • Some lymphoid progenitors are by interleukin-3 to become a basophil. released (and transported through the blood) to the thymus where Agranulocytes they mature to become T-lympho- The cytoplasm of the agranulocyte is rel­ cytes (hence the name T-cell). atively clear. Formation of agranulocytes • Other lymphoid progenitors is called agranulopoiesis. There are two remain in the bone marrow where types of agranular leukocytes: monocytes they are further stimulated by and lymphocytes. interleukin-6 to become B-lym- phocytes (hence the name B-cell). Monocytes Monocytes account for approximately B-Lymphocytes 3%-7% of all leukocytes and are the B-lymphocytes circulate through largest of all leukocytes. Monocytes the body in the blood, but concen­ mature as they enter the blood stream trate in certain tissues (eg, liver), or to become macrophages. Macrophages the lymphoid organs such as the are large phagocytes that migrate to lymph nodes, tonsils, and the the tissues (especially the liver, lungs, spleen. B-cells are specific only to and lymph nodes) and engulf particu­ one type of antigen and produce late matter such as antigens (foreign only one type of antibody. B-cells material) and dying or dead body cells. divide mitotically in the bone mar­ Monocytes along with T and B-lym- row producing more lymphocytes phocytes are important in the immune (clones) containing the genetic response system. material for the same antibody. Monocytes develop from the granu­ There are two main types of B-cells: locyte macrophage progenitor (refer to plasma cells and memory cells.

The Surgical Technologist JUNE 2003 20 Plasma cells produce and release blood clotting process (cascade). When a vas­ an antibody specific to a certain cular injury occurs, thrombocytes are attract­ type of antigen. Memory cells con­ ed by and adhere to exposed collagen on the tain antibody information specific blood vessel wall. The clumped (aggregated) to a certain type of antigen. If the thrombocytes swell and release ADP con­ same antigen is encountered again, tained in their granules causing more throm­ the memory cells divide rapidly bocytes to adhere to the site forming a plug replicating the specific plasma cells and thereby reducing blood loss. They also and producing more memory cells. release chemicals that cause vascular spasm at Because of the memory cells, the a site of injury. The lifespan of a thrombo­ body’s second response to the anti­ cyte is approximately four days. gen is more rapid. The process of thrombopoiesis (platelet production) is as follows: T-Lymphocytes T-lymphocytes have specific cell • The pluripotent stem cell is stimulated by receptors on their surface that are the hormone thrombopoietin (secreted similar to antibodies and are speci­ by the liver) to become a blood cell (red fic to one antigen. T-cells are acti­ blood cell, white blood cell—with the vated during contact with an anti­ exception of the lymphocyte, or a platelet) gen. The T-cell with the specific in the myeloid tissue (myeloid progeni­ antibody responds by dividing tor). mitotically. There are three main • The myeloid progenitor is stimulated by types of T-cells: helper T-cells, erythropoietin to produce the megakary- killer T-cells, and memory T-cells. ocyte/erythroid progenitor, which is the Helper T-cells release cytokines differentiated stem cell that will eventual­ when the receptors on their surface ly become the erythrocyte or the throm­ are activated. The cytokines stimu­ bocyte. late the related B-cells to divide into • The megakaryocyte/erythroid progenitor plasma cells that make the anti­ is again stimulated by thrombopoietin as body. The cytokines also stimulate well as interleukin-11 to become the macrophagic phagocytosis. megakaryocyte. Killer T-cells (sometimes called • The megakaryocyte replicates its DNA natural killer cells) search for and repeatedly while still in the bone marrow, bind to body cells affected by an the cell enlarges but does not divide. invader displaying a certain anti­ • The megakaryocyte ruptures and frag­ gen. The killer T-cells kill both the ments of the cytoplasm (thrombocytes) invader and the affected cell by enter the blood. attaching to the cell and secreting a • Some thrombocytes remain in circulation toxin such as hydrogen peroxide. while others are stored in the spleen and Memory T-cells are similar to released as needed. memory B-cells because they initi­ ate a more rapid response if the Plasma same antigen is reencountered. Plasma, the straw-colored liquid element of blood, is made up of approximately 90% water. Thrombocytes The remaining 10% consists of a variable num­ Thrombocytes are small nonnucleated cell ber of substances such as proteins, nutrients, fragments. Thrombocytes are part of the amino acids, lipids, electrolytes, vitamins, hor-

JULY 2003 The Surgical Technologist 21 mones, drugs, and waste products that are either References suspended or dissolved in the water. Variations 1. Blood (2002). Kimball, JW. Kimball’s Biology occur as substances are added and removed from Pages. users.rcn.com/jkimball.ma.ultranet/Biology the plasma as the blood circulates through the Pages/B/Blood.html Accessed 1-2-03 tissues. Proteins account for the largest percent­ 2. Blood and Cardiovascular Physiology (2001). age of material in the plasma. Plasma is the Fyffe, WE. Northwest Nazarene University. transportation medium for the corpuscles. courses.nnu.edu/bi362bf/newpage4.htm Accessed 1-2-03 3. Human Anatomy & Physiology, second edi­ Serum tion (1990). Solomon, EP, Schmidt, RR, Serum is what remains of the plasma when Adragna, PJ. Saunders: Fort Worth, TX. the clotting factors are removed. 4. Surgical Technology for the Surgical Technolo­ gist: A Positive Care Approach (2001). Note: Many factors influence hematopoiesis—not Caruthers B, et al. Delmar Thompson Learn­ all are listed in this brief article. ing: Albany, New York. 5. The Anatomy and Physiology Learning System About the author (1995). Applegate, E. W.B. Saunders Compa­ Teri Junge, CST/CFA, is currently the surgical ny: Philadelphia, PA. technology program director for the San Joaquin 6. The Blood (1994). Corrigan, D. Association of Valley College, Fresno, California. While on Surgical Technologists: Englewood, CO. AST’s staff as medical editor, she wrote numer­ 7. The Human Body in Health & Disease, eighth ous Journal articles and educational materials, edition (1996). Memmler, RL, Cohen, BJ, including chapters for the future second edition Wood, DL. Lippincott: Philadelphia, PA. of the textbook, Surgical Technology for the Surgi­ cal Technologist: A Positive Care Approach.

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