Hematopoietic System PDF

HEMATOPOIETIC SYSTEM SYSTEM COORDINATOR: DR. FRANCES ANGELIQUE TEQUILLO BLOCK 4 MODULE 1 (CASES 1 AND 2) BASIC BIOMEDICAL SCIENCES I NOT FOR SALE | DO NOT UPLOAD IN ONLINE SITE...

HEMATOPOIETIC SYSTEM SYSTEM COORDINATOR: DR. FRANCES ANGELIQUE TEQUILLO BLOCK 4 MODULE 1 (CASES 1 AND 2) BASIC BIOMEDICAL SCIENCES I NOT FOR SALE | DO NOT UPLOAD IN ONLINE SITES ------------------------------------------------------------------------------------------------------------------------------------------------------- CASE 1 BLOOD COMPONENTS AND PHYSICAL CHARACTERISTICS Blood is a specialized connective tissue consisting of cells and fluid extracellular material called plasma. o Propelled mainly by rhythmic contractions of the heart, about 5 L of blood in an average adult moves unidirectionally within the closed circulatory system. o The so-called formed elements circulating in the plasma are erythrocytes (red blood cells), leukocytes (white blood cells [WBCs]), and platelets. When blood leaves the circulatory system, either in a test tube or in the extracellular matrix (ECM) surrounding blood vessels, plasma proteins react with one another to produce a clot, which includes formed elements and a pale yellow liquid called serum. o Serum contains growth factors and other proteins released from platelets during clot formation, which confer biological properties very different from those of plasma. Collected blood in which clotting is prevented by the addition of anticoagulants (e.g., heparin or citrate) can be separated by centrifugation into layers that reflect its heterogeneity. o Erythrocytes comprise the sedimented material, and their volume, normally about 44% of the total blood volume in healthy adults, is called the hematocrit. The straw-colored, translucent, slightly viscous supernatant comprising 55% at the top half of the centrifugation tube is the plasma. o A thin gray-white layer called the buffy coat between the plasma and the hematocrit, about 1% of the volume, consists of leukocytes and HEMATOPOIESIS platelets, both less dense than erythrocytes. Definition Blood is a distributing vehicle, transporting O2, CO2, metabolites, o Hematopoiesis is defined as the production, development, hormones, and other substances to cells throughout the body. differentiation, and maturation of all blood cells. o Most O2 is bound to hemoglobin in erythrocytes and is much more Differentiation as to site of production before and after birth abundant in arterial than venous blood, while CO2 is carried in solution o The bone marrow is extremely versatile and serves the body well by as CO2 or HCO3-, in addition to being hemoglobin-bound. supplying life-giving cells with a multiplicity of functions. Various o Nutrients are distributed from their sites of synthesis or absorption in organs serve a role in hematopoiesis, and these organs differ from the gut, while metabolic residues are collected from cells throughout fetal to adult development. the body and removed from the blood by the excretory organs. o The yolk sac, liver, and spleen are the focal organs in fetal o Hormone distribution in blood permits the exchange of chemical development. messages between distant organs regulating normal organ function.  From 2 weeks until 2 months in fetal life, most erythropoiesis o Blood also participates in heat distribution, the regulation of body occurs in the fetal yolk sac. This period of development, known as temperature, and the maintenance of acid-base and osmotic balance. the mesoblastic period, produces primitive erythroblasts and Leukocytes have diverse functions and are one of the body’s chief embryonic hemoglobins (Hgbs) such as Hgb Gower I and Gower II defenses against infection. and Hgb Portland. o These cells are generally spherical and inactive while suspended in  These hemoglobins are constructed as tetramers with 2 alpha circulating blood, but when called to sites of infection or inflammation, chains combined with either epsilon or zeta chains. they cross the wall of venules, become motile and migrate into the  As embryonic hemoglobins, they do not survive into adult life or tissues, and display their defensive capabilities. participate in oxygen delivery. Composition of Plasma  During the hepatic period, which continues from 2 months through o Plasma is an aqueous solution, pH 7.4, containing substances of low 7 months of fetal life, the liver and spleen take over the or high molecular weight that make up 7% of its volume. hematopoietic role. White blood cells and megakaryocytes begin o The dissolved components are mostly plasma proteins, but they also to appear in small numbers. include nutrients, respiratory gases, nitrogenous waste products,  The liver serves primarily as an erythroid-producing organ but hormones, and inorganic ions collectively called electrolytes. also gives rise to fetal hemoglobin, which consists of alpha and o Through the capillary walls, the low-molecular-weight components of gamma chains. plasma are in equilibrium with the interstitial fluid of the tissues.  The spleen, thymus, and lymph nodes also become o The composition of plasma is usually an indicator of the mean hematopoietically active during this stage, producing red blood composition of the extracellular fluids in tissues. cells and lymphocytes. o The major plasma proteins include the following:  However, from 7 months until birth, the bone marrow assumes the  Albumin, the most abundant plasma protein, is made in the liver primary role in hematopoiesis, a role that continues into adult life. and serves primarily to maintain the osmotic pressure of the blood.  Additionally, Hgb A, the majority adult hemoglobin (alpha 2, beta  Globulins (α- and β-globulins), made by the liver and other cells, 2), begins to form. The full complement of Hgb A is not realized include transferrin and other transport factors; fibronectin; until 3 to 6 months postpartum, as gamma chains from Hgb F prothrombin and other coagulation factors; lipoproteins and other are diminished and beta chains increase. proteins entering blood from tissues.  In a normal individual 6 months old or older, 95% to 98% of the  Immunoglobulins (antibodies or γ-globulins) secreted by plasma total hemoglobin is Hgb A, 2% to 5% is Hgb A2, and less than 2% cells in many locations. is Hgb F.  Fibrinogen, the largest plasma protein (340 kD), also made in the Differentiation between intramedullary and extramedullary liver, which, during clotting, polymerizes as insoluble, cross-linked Hematopoiesis fibers of fibrin that block blood loss from small vessels. o Hematopoiesis within the bone marrow is termed intramedullary  Complement proteins, which comprise a defensive system hematopoiesis. The term extramedullary hematopoiesis describes important in inflammation and destruction of microorganisms. hematopoiesis outside the bone marrow environment, primarily in the 1  liver and spleen. Because these organs play major roles in early fetal  Most of the reproduced cells, however, differentiate to form the other hematopoiesis, they retain their hematopoietic memory and capability. cell types, shown at the right in Figure 33-2. The intermediate stage o The liver and spleen can function as organs of hematopoiesis if cells are very much like the multipotential stem cells, even though needed in adult life. Several circumstances within the bone marrow they have already become committed to a particular line of cells; (e.g., infiltration of leukemic cells, tumor) may diminish the normal these are called committed stem cells. hematopoietic capability of the bone marrow and force these organs o The different committed stem cells, when grown in culture, will produce to perform again as primary or fetal organs of hematopoiesis. colonies of specific types of blood cells. o If extramedullary hematopoiesis develops, the liver and spleen  A committed stem cell that produces erythrocytes is called a colony- become enlarged, a condition known as hepatosplenomegaly. forming unit-erythrocyte (CFU-E).  Likewise, colony-forming units that form granulocytes and monocytes have the designation CFU-GM, and so forth. FORMED ELEMENTS OF BLOOD Development o The formed elements of blood (red cells, granulocytes, monocytes, platelets, and lymphocytes) have a common origin from hematopoietic o Growth and reproduction of the different stem cells are controlled by stem cells (HSCs), pluripotent cells that sit at the apex of a hierarchy multiple proteins called growth inducers. of bone marrow progenitors.  At least four major growth inducers have been described, each o The development of mature blood cells from HSCs involves having different characteristics. One of these, interleukin-3, progressive commitment to increasingly specialized cell populations. promotes growth and reproduction of virtually all the different types o HSCs give rise to several kinds of early progenitor cells that have of committed stem cells, whereas the others induce growth of only more restricted differentiation potential, such that they ultimately specific types of cells. produce mainly myeloid cells or lymphoid cells. These early o The growth inducers promote growth but not differentiation of the cells, progenitors in turn give “birth” to progenitors that are further which is the function of another set of proteins called differentiation constrained in their differentiation potential. inducers. o Some of these cells are referred to as colony-forming units because  Each of these differentiation inducers causes one type of committed they produce colonies composed of specific kinds of mature cells stem cell to differentiate one or more steps toward a final adult blood when grown in culture. cell. o From the various committed progenitors are derived the o Formation of the growth inducers and differentiation inducers is morphologically recognizable precursors, such as myeloblasts, controlled by factors outside the bone marrow. proerythroblasts, and megakaryoblasts, which are the immediate  In the case of RBCs, exposure of the blood to a low oxygen level for progenitors of mature granulocytes, red cells, and platelets. a long time causes growth induction, differentiation, and production of greatly increased numbers of RBCs.  In the case of some of the WBCs, infectious diseases cause growth, differentiation, and eventual formation of specific types of white blood cells that are needed to combat each infection. o Erythropoietin Regulates Red Blood Cell Production  The total mass of RBCs in the circulatory system is regulated within narrow limits, and thus (1) an adequate number of RBCs are always available to provide sufficient transport of oxygen from the lungs to the tissues, yet (2) the cells do not become so numerous that they impede blood flow. This control mechanism is diagrammed: Mechanism of production and release o The blood cells begin their lives in the bone marrow from a single type  Example: When a person’s Hgb level is below normal, the oxygen of cell called the multipotential hematopoietic stem cell, from which content of the blood drops and the oxygen tension in the kidneys is all the cells of the circulating blood are eventually derived. reduced (hypoxia). This will stimulate the kidneys to increase their  Figure 33-2 shows the successive divisions of the multipotential cells production of erythropoietin, which will make its way through the to form the different circulating blood cells. As these cells reproduce, circulation and locks onto a receptor on the pronormoblast a small portion of them remains exactly like the original multipotential stimulating the production of 16 mature red cells from every cells and is retained in the bone marrow to maintain their supply, pronormoblast precursor cell. although their numbers diminish with age. 2  ERYTHROCYTIC (RED CELL) SERIES General descriptions o Erythrocytes (red blood cells [RBCs]) are terminally differentiated structures lacking nuclei and completely filled with the O2-carrying Functions protein hemoglobin. RBCs are the only blood cells whose function o A major function of RBCs is to transport hemoglobin, which, in turn, does not require them to leave the vasculature. carries oxygen from the lungs to the tissues. o Human erythrocytes suspended in an isotonic medium are flexible  In some animals, including many invertebrates, hemoglobin biconcave discs. circulates as free protein in the circulatory fluids and is not enclosed  They are approximately 7.5 μm in diameter, 2.6-μm thick at the rim, in RBCs. but only 0.75-μm thick in the center.  When it is free in human plasma, about 3% of it leaks through the  Because of their uniform dimensions and presence in most tissue capillary membrane into the tissue spaces or through the glomerular sections, RBCs can often be used by histologists as an internal membrane of the kidney into the glomerular filtrate each time the standard to estimate the size of other nearby cells or structures. blood passes through the capillaries. Therefore, hemoglobin must o The biconcave shape provides a large surface-to-volume ratio and remain inside RBCs to perform its functions in humans effectively. facilitates gas exchange. The normal concentration of erythrocytes in o The RBCs have other functions besides transport of hemoglobin. blood is approximately 3.9-5.5 million per microliter (μL, or mm3) in  For example, they contain a large quantity of carbonic anhydrase, women and 4.1-6.0 million/μL in men. an enzyme that catalyzes the reversible reaction between carbon o Erythrocytes are normally quite flexible, which permits them to bend dioxide (CO2) and water to form carbonic acid (H2CO3), increasing and adapt to the small diameters and irregular turns of capillaries. the rate of this reaction several thousandfold. The rapidity of this  Observations in vivo show that at the angles of capillary bifurcations, reaction makes it possible for the water of the blood to transport erythrocytes with normal adult hemoglobin frequently assume a enormous quantities of CO2 in the form of bicarbonate ion (HCO3−) cuplike shape. from the tissues to the lungs, where it is reconverted to CO2 and  In larger vessels within microvasculature, RBCs may adhere to one expelled into the atmosphere as a body waste product. another loosely in stacks called rouleau, particularly in conditions of  The hemoglobin in the cells is an excellent acid-base buffer (as is low flow velocity or increased plasma viscosity. true of most proteins), so the RBCs are responsible for most of the o The erythrocyte plasmalemma, because of its ready availability, is the acid-base buffering power of whole blood. best-known membrane of any cell. Stages of development and Morphology of each stage  It consists of about 40% lipid, 10% carbohydrate, and 50% protein. o Rubriblast (Pronormoblast/Proerythroblast)  Most of the latter are integral membrane proteins, including ion  The rubriblast is the earliest erythrocyte precursor identified by light channels, the anion transporter called band 3 protein, and microscopy in the stained bone marrow sample. glycophorin A.  Cell size is variable, ranging from 12 to 25 μm.  The glycosylated extracellular domains of the latter proteins include  The nucleus:cytoplasm (N:C) ratio is high, with the nucleus antigenic sites that form the basis for the ABO blood typing system. usually occupying more than 80% of the cell.  Several peripheral proteins are associated with the inner surface of  The cytoplasm is basophilic (intense dark blue) because of the high the membrane, including spectrin, dimers of which form a lattice RNA content, which attracts the basic part of the stain (e.g., bound to underlying actin filaments, and ankyrin, which anchors the methylene blue). spectrin lattice to the glycophorins and band 3 proteins.  The Golgi apparatus may be visible as a pale area next to the  This submembranous meshwork stabilizes the membrane, nucleus. maintains the cell shape, and provides the cell elasticity required for  The nucleus is usually round to slightly oval, has dispersed fine passage through capillaries. clumps of chromatin, and contains nucleoli. o Erythrocyte cytoplasm lacks all organelles but is densely filled with  At times it is difficult to differentiate the rubriblast from a myeloblast hemoglobin, the tetrameric O2-carrying protein that accounts for the (the earliest identifiable stage of granulopoiesis). However, a cells’ uniform acidophilia. myeloblast usually has less cytoplasmic basophilia and a fine, lacy  When combined with O2 or CO2, hemoglobin forms oxyhemoglobin chromatin that stains less intensely than the rubriblast. or carbaminohemoglobin, respectively. The reversibility of these  At this stage of maturation, the degree of basophilia probably is more combinations is the basis for the protein’s gas-transporting capacity. helpful than nuclear characteristics in distinguishing between the o Erythrocytes undergo terminal differentiation, which includes loss of two. The rubriblast gives rise to two prorubricytes. the nucleus and organelles shortly before the cells are released by o Prorubricyte (Basophilic Normoblast/Basophilic Erythroblast) bone marrow into the circulation.  The prorubricyte is slightly smaller (12-17 μm) than the rubriblast  Lacking mitochondria, erythrocytes rely on anaerobic glycolysis for with the nucleus usually occupying 75% of the cell. their minimal energy needs.  The cytoplasm is basophilic, and the Golgi apparatus is usually  Lacking nuclei, they cannot replace defective proteins. visible as a light area near the nucleus. o Human erythrocytes normally survive in the circulation for about 120  The nucleus is round, and its chromatin is dark violet and definitely days. coarser and more clumped than that in the rubriblast.  By this time, defects in the membrane’s cytoskeletal lattice or ion  Parachromatin, the nonstaining or clear area of the nucleus, is transport systems begin to produce swelling or other shape slightly visible between the clumps of chromatin. abnormalities, as well as changes in the cells’ surface  Usually, nucleoli are no longer visible. oligosaccharide complexes.  The coarser chromatin and the absence of nucleoli are the most  Senescent or worn-out RBCs displaying such changes are helpful criteria in distinguishing the prorubricyte from the rubriblast. recognized and removed from circulation, mainly by macrophages  The prorubricyte divides 2 times, giving rise to 4 rubricytes. of the spleen, liver, and bone marrow. o Rubricyte (Polychromatophilic Normoblast/Polychromatophilic Erythroblast)  The rubricyte is usually smaller (12-15 μm) than the prorubricyte.  It has a round nucleus that may be eccentric.  Throughout this stage of maturation, more cytoplasm becomes apparent as the nucleus becomes smaller.  The cytoplasm shows a varied spectrum of blue color as Hb is synthesized. Blue RNA mixed with red Hb gives the cytoplasm an opaque, violet-blue color called polychromasia. 3   Early rubricyte cytoplasm is moderately polychromatophilic, and basophils. All granulocytes are also terminally differentiated cells differing from the intensely dark blue cytoplasm of the prorubricyte. with a life span of only a few days after leaving the bloodstream.  Late rubricytes have a paler blue-gray-violet to slightly pinkish color. o Their Golgi complexes and rough ER are poorly developed, and with  The nuclear chromatin is very coarse and condensed. few mitochondria they depend largely on glycolysis for their energy  Distinct areas of parachromatin are visible amid clumps of needs. chromatin. This cell may be confused with a lymphocyte. o Most granulocytes undergo apoptosis in the connective tissue and  Each rubricyte gives rise to 2 metarubricytes. This is the last cell billions of neutrophils alone die each day in adults. The resulting division during maturation. cellular debris is removed by macrophages and, like all apoptotic cell o Metarubricyte (Orthochromic Normoblast/Orthochromic death, does not itself elicit an inflammatory response. Erythroblast) o In general, as granulocytes mature, the nuclear chromatin becomes  The metarubricyte is the last nucleated erythrocyte stage. It is the more condensed, nucleoli disappear, and abundant basophilic same size as or slightly smaller than the rubricyte (8-12 μm). cytoplasm with non-specific granulation progresses to more scant  The distinguishing features of this cell are its paler, blue-gray-violet cytoplasm containing granulation specific for the eosinophil, basophil, polychromatophilic to pinkish cytoplasm and dense nuclear or neutrophil. The nucleus indents and the overall cell size decreases. chromatin pattern. o Neutrophils  The nucleus is pyknotic (dense mass of degenerated chromatin),  General descriptions and Hb is the main constituent of the cytoplasm.  Mature neutrophils constitute 50%-70% of circulating leukocytes,  The nucleus is extruded at this stage, and the cell becomes a a figure that includes slightly immature forms released to the reticulocyte. circulation. o Reticulocyte (Diffusely Basophilic Erythrocyte/  Neutrophils are 12-15 μm in diameter in blood smears, with nuclei Polychromatophilic Erythrocyte) having 2-5 lobes linked by thin nuclear extensions.  The reticulocyte is slightly larger than the mature erythrocyte and  In females, the inactive X chromosome may appear as a may have irregular cytoplasmic borders. drumstick-like appendage on one of the lobes of the nucleus  The cytoplasm still contains small amounts of RNA, giving the cell although this characteristic is not always seen. various degrees of polychromasia (mixed pink and blue staining).  Neutrophils are inactive and spherical while circulating but  After nuclear expulsion, reticulocytes are retained in the marrow for become amoeboid and highly active during diapedesis and upon 2 to 3 days before release into the marrow sinusoids to appear in adhering to ECM substrates such as collagen. the peripheral blood. The mechanism for their release is unknown,  Neutrophils are usually the first leukocytes to arrive at sites of and many factors probably are involved. Perhaps as the erythrocyte infection where they actively pursue bacterial cells using matures, it loses its ability to adhere to fibronectin, a glycoprotein in chemotaxis and remove the invaders or their debris by the bone marrow matrix. phagocytosis.  The reticulocyte contains Golgi apparatus remnants and residual  The cytoplasmic granules of neutrophils provide the cells’ mitochondria that permit continued aerobic metabolism and Hb functional activities and are of two main types: production, which decrease as the cell matures.  Azurophilic primary granules or lysosomes are large, dense  Reticulocytes also contain residual RNA, which may be stained vesicles with a major role in both killing and degrading engulfed supravitally (in the living state) using stains such as new methylene microorganisms. They contain proteases and antibacterial blue or brilliant cresyl blue. proteins, including the following:  Such staining causes the RNA to precipitate and aggregate into a  Myeloperoxidase (MPO), which generates hypochlorite and network of strands or clumps visible by light microscopy. other agents toxic to bacteria  These stains permit laboratory performance of reticulocyte counts  Lysozyme, which degrades components of bacterial cell walls and calculation of the reticulocyte production index (RPI) for  Defensins, small cysteine-rich proteins that bind and disrupt evaluation of the effectiveness of erythropoiesis in anemic states. the cell membranes of many types of bacteria and other  Within 24 to 48 hours, the cell loses the organelles and assumes a microorganisms biconcave shape. It is then a mature erythrocyte.  Specific secondary granules are smaller and less dense, stain o Mature Erythrocyte faintly pink, and have diverse functions, including secretion of  The mature erythrocyte is approximately 7.2 μm in diameter. various ECM-degrading enzymes such as collagenases,  In a resting state it is a biconcave disc, thus the name discocyte. delivery of additional bactericidal proteins to phagolysosomes,  With Wright stain, a central pale area is seen that fades gradually and insertion of new cell membrane components. into reddish-pink cytoplasm. The central pallor corresponds to the  Activated neutrophils at infected or injured sites also have indentation in the erythrocyte disc. important roles in the inflammatory response, which begins the  The mature erythrocyte contains no mitochondria; therefore, neither process of restoring the normal tissue microenvironment. proteins nor Hb is synthesized.  They release many polypeptide chemokines that attract other LEUKOCYTIC (WHITE CELL) SERIES leukocytes and cytokines, which direct activities of these and The white blood cell series encompasses cells that are distinguished by local cells of the tissue. Important lipid mediators of their granules and cells that are agranular. In all, there are 5 inflammation are also released from neutrophils. morphologically distinct maturation stages for neutrophils, 4 for  Neutrophils contain glycogen, which is broken down into glucose eosinophils and basophils, and 3 for monocytes and lymphocytes. to yield energy via the glycolytic pathway. Key features in distinguishing immature and mature stages of any of  The citric acid cycle is less important, as might be expected in these cells are: cell size, nucleus:cytoplasm ratio (N:C), chromatin view of the paucity of mitochondria in these cells. pattern, presence or absence of nucleoli, cytoplasmic quality, and  The ability of neutrophils to survive in an anaerobic environment presence of granules. is highly advantageous, because they can kill bacteria and help Nucleoli are a unique feature of immature cells and represent structures clean up debris in poorly oxygenated regions, for example, within the chromatin that appear lighter, more refractile, and more damaged or necrotic tissue lacking normal microvasculature. recognizable.  Neutrophils are short-lived cells with a half-life of 6-8 hours in Granulocytes blood and a life span of 1-4 days in connective tissues before o Granulocytes possess two major types of abundant cytoplasmic dying by apoptosis. granules: lysosomes (often called azurophilic granules in blood cells)  For each neutrophil in the blood vessels, about 16 precursors are and specific granules that bind neutral, basic, or acidic stains and present in the marrow. have specific functions.  From the time of differentiation into a myeloblast, through about o Granulocytes also have polymorphic nuclei with two or more distinct 5 mitotic divisions (3 of which occur at the myelocyte stage), it (almost separated) lobes and include the neutrophils, eosinophils, takes about 14 days until the progeny of that cell reach the blood. 4   The last 6-7 days are spent in the maturation and storage pool.  The nucleus becomes more condensed and the chromatin  When a neutrophil enters the blood, it moves readily between a pattern clumped; nucleoli usually are no longer visible. The N:C circulating granulocyte pool, which is sampled in the leukocyte ratio continues to decrease. count, and a marginal granulocyte pool, which is not, but is either  The cell size ranges from 16 to 24 μm. marginated along vessel walls or sequestered in capillary beds.  Myelocytes are the last stage to undergo mitosis. Cells in  In less than 1 day after it arrives, the neutrophil emigrates from the subsequent stages continue to mature but do not divide. circulation in a random manner and enters the tissues.  Neutrophilic myelocytes make up approximately 10% to 20% of  Migration into tissues is dependent on adhesion molecules of the marrow cells and normally are not seen in peripheral blood. selectin family (and their corresponding ligands) expressed on  The secondary granules contain lysozyme, acid hydrolases, neutrophils and endothelial cells. and a variety of other proteins but not peroxidase.  From there, if not utilized in an inflammatory exudate, neutrophils  Metamyelocyte leave the body within a few days via secretions in bronchi, saliva,  The cell next matures into a metamyelocyte (also called a the gastrointestinal tract, and urine, or they are destroyed by the juvenile), and the shape of the nucleus becomes the chief mononuclear phagocyte system. identification criterion.  Stages of development and Morphology  Until this stage, the nucleus has remained round or oval, but  Myeloblast now it begins to flatten on one side and begins to constrict or  The earliest recognizable form that can be identified by light indent (becoming kidney-bean or peanut-shaped). Nuclear microscopy as a cell that will mature into one of the myeloid cells chromatin condenses even more to become coarsely clumped. is the myeloblast.  The cytoplasm has lost all traces of blue color (RNA) and  This cell has dark blue to blue cytoplasm that contains no appears uniformly pink with pinkish purple secondary granules visible granules. evenly distributed, much as in the cytoplasm of the mature cell.  The nucleus is made up of a smooth, delicate, uniformly  Metamyelocytes make up approximately 15% to 30% of marrow distributed chromatin pattern sometimes described as lacy. cells and normally are not found in the peripheral blood.  Myeloblasts usually have 2 or more distinct nucleoli, which  To differentiate this stage from the next more mature stage (the disappear as the cell matures. band), the indentation of the nucleus must be less than half the  The nucleus occupies most of the cell, leaving only a small rim width of the nucleus. of cytoplasm. This is referred to as a high N:C ratio.  Band (Stab/Staff Cell/Non-segmented Neutrophil)  The approximate cell diameter is 15 to 20 um, de-pending on  This is the last stage before the mature cell. Bands are normally what stage in the mitotic cycle it is in. Cells become relatively present in a small percentage in peripheral blood. larger just prior to mitotic division.  Nucleus: Elongated, curved, or sausage shaped with rounded  Myeloblasts make up about 1% to 2% of the cells in normal bone ends and areas of dense clumping at each pole. The beginning marrow and normally are not seen in peripheral blood. of segmentation may be apparent, but the connecting band  Promyelocyte (Progranulocyte) between lobes is wide enough to reveal two distinct margins  At the first appearance of cytoplasmic granules, the cell is surrounding nuclear material. Filaments are not present. placed in the promyelocyte stage. It is characterized by large,  Cytoplasm: Stains light pink with numerous specific or prominent, reddish purple granules in the cytoplasm called secondary granules that are too small to be resolved individually primary or azurophilic granules. with the light microscope and give the cytoplasm a grainy  The background cytoplasm remains dark blue to blue, and the appearance. A few purple primary granules may remain. nucleus still appears fairly immature with a uniform, evenly  Segmented Neutrophil distributed chromatin pattern.  Nucleus: Segmented into 2-5 lobes; lobes are connected by a  Nucleoli may or may not be visible. threadlike filament that does not contain chromatin. Nuclear  As the cell matures, the nucleus may be displaced off center and chromatin is dark purple and forms densely stained clumps the nuclear-cytoplasmic ratio decreases. separated by a network of lighter purple bands.  This cell is still rather large and may sometimes appear larger  Cytoplasm: Identical to that of the band stage than the myeloblast, depending on its stage in the mitotic cycle.  Functions  Promyelocytes make up 2% to 5% of cells in the bone marrow  Neutrophils are able to move in a zigzag manner, but their motion and normally are not found in the peripheral blood. changes to a straight-line path if a chemotactic attractant or factor  Synthesis of primary granules begins and ends during this stage. (e.g., a bacterium coated with certain components of complement)  As the cell continues to divide, primary granules are diluted is within a certain distance. among daughter cells. These granules, which are rich in the  Neutrophils express chemokine receptors CXCR1 and CXCR2, enzyme peroxidase, are present in all stages including the which are responsible for neutrophil migration in response to mature segmented neutrophil, but they become less visible chemokines. with Wright or a comparable stain.  Neutrophils also have receptors for the Fc portion of IgG as well  Evidence of this is the intense staining by peroxidase stains in as for complement (C3) and bind and phagocytose the coated the cytoplasm of mature neutrophils. particle.  Myelocyte  Phagocytosis occurs with the formation of a phagocytic vacuole  Myelocytes begin to form a second set of granules referred to that contains the ingested particle; accompanying this process is as secondary or specific granules. an increase in metabolic activity and energy production.  The primary granules become less visible as the secondary  Specific granules, followed shortly by azurophilic granules, granules are being formed, thus cells in this stage may have empty their contents into the phagocytic vacuoles- a process varying amounts of each type of granule. known as degranulation.  Secondary granules are smaller and are the granules that  Bactericidal activity occurs within the vacuole, mediated by eventually fill the cell and give it its characteristic pinkish tan hydrogen peroxide (H2O2), superoxide anion (O2−), color. myeloperoxidase, and a halide ion generating free halogen, or by  The cytoplasm of the cell begins to lose cytoplasmic RNA (blue other enzymatic activity. color), but a tinge of blue may remain, especially along the  Other substances can act as chemotactic factors as well. edges of the cell. As the pinkish specific granules begin to form  The C5a fragment is a chemotactic factor and is also an in the Golgi region of the cell, a pink arc may be seen, which is anaphylatoxin that causes smooth muscle contraction. sometimes called the “dawn of neutrophilia.”  Substances liberated by bacteria and metabolic products of arachidonic acid may also act as chemotactic factors for neutrophils. 5   Neutrophils are thus important in defense against infectious substances that inactivate factors released by mast cells and disease. If their enzymes are activated and released outside the basophils, such as histamine, slow-reacting substances of cell, neutrophils can cause tissue necrosis, tissue injury, and anaphylaxis, and platelet-activating factor (PAF). inflammation.  When an intense or prolonged eosinophilic inflammatory reaction o Eosinophils occurs, there is often the formation of Charcot-Leyden crystals.  General descriptions  These hexagonal bipyramidal crystals are composed of  Eosinophils are far less numerous than neutrophils, constituting lysophospholipase localized in the cytoplasm of eosinophils. only 1%-4% of leukocytes. o Basophils  In blood smears, this cell is about the same size as a neutrophil or  General descriptions slightly larger, but with a characteristic bilobed nucleus.  Basophils are also 12-15 μm in diameter but make up less than  The main identifying characteristic is the abundance of large, 1% of circulating leukocytes and are therefore difficult to find in acidophilic-specific granules typically staining pink or red. normal blood smears.  Ultrastructurally, the eosinophilic-specific granules are seen to be  The nucleus is divided into two irregular lobes, but the large oval in shape, with flattened crystalloid cores containing major specific granules overlying the nucleus usually obscure its shape. basic proteins (MBP), an arginine-rich factor that accounts for  The specific granules (0.5 μm in diameter) typically stain purple the granule’s acidophilia and constitutes up to 50% of the total with the basic dye of blood smear stains and are fewer, larger, and granule protein. MBPs, along with eosinophilic peroxidase, more irregularly shaped than the granules of other granulocytes. other enzymes and toxins, act to kill parasitic worms or helminths.  The strong basophilia of the granules is due to the presence of  Eosinophils also modulate inflammatory responses by releasing heparin and other sulfated GAGs. chemokines, cytokines, and lipid mediators, with an important role  Basophilic-specific granules also contain much histamine and in the inflammatory response triggered by allergies. various other mediators of inflammation, including platelet  The number of circulating eosinophils increases during helminthic activating factor, eosinophil chemotactic factor, and the infections and allergic reactions. enzyme phospholipase A that catalyzes an initial step in  These leukocytes also remove antigen-antibody complexes from producing lipid-derived proinflammatory factors called interstitial fluid by phagocytosis. leukotrienes.  Eosinophils are particularly abundant in connective tissue of the  By migrating into connective tissues, basophils appear to intestinal lining and at sites of chronic inflammation, such as lung transiently supplement the functions of mast cells. tissues of asthma patients.  Like mast cells, basophils have surface receptors for IgE, and  The kinetics of eosinophils are similar to those of neutrophils. They secrete heparin and histamine in response to various antigens are stored in the bone marrow for several days after going through and allergens. various maturational stages.  Basophils have a life span similar to eosinophils. The maturation  The half-life in the blood is approximately 18 hours before time in the marrow is approximately 7 days. entering the tissues, where they survive for at least 6 days.  Basophils circulate in the blood and are not normally found in  Eosinophils in the tissues, however, are at least 100 times as tissues, in contrast to mast cells, which can spend 9-18 months numerous as the total number of eosinophils in the blood; they are in connective tissue. located primarily in skin, lung, and gastrointestinal tract (i.e., the  GM-CSF, IL-3, and IL-5 influence basophil production. epithelial barriers to the outside world).  However, IL-3 is the principal growth factor for basophilic growth,  Morphology whereas c-kit ligand enhances the number and activation state  They undergo the same maturation stages as the neutrophil in the of mast cells bone marrow and spend a short time in the blood in transit to the  Morphology tissues where they perform their functions.  Basophils are formed in the bone marrow, and their maturation  Immature eosinophils have a few large blue granules, which are stages parallel those of the neutrophil except that the nucleus lost by attrition as the cell undergoes subsequent mitotic divisions. does not always segment.  As the cell matures, specific granules form and take on a refractive,  Mature Basophil orange appearance.  Nucleus: Light purple staining, may be round, indented, band  Mature Eosinophil shaped, or lobulated. Usually difficult to see because of  Nucleus: Dark purple, chromatin pattern similar to neutrophil; overlying granules. Chromatin pattern is smudged and indistinct. usually band shaped or segmented into only two segments.  Cytoplasm: Characterized by densely stained, dark violet to  Cytoplasm: Filled with large, spherical, refractive granules of purple-black granules that are variable in size and unevenly uniform size that stain bright orange-pink. The granules are distributed. Because the granules are water soluble, only usually evenly distributed but rarely overlie the nucleus. vestiges of granules, sometimes contained within small  Functions vacuoles, may be found.  Eosinophils act as phagocytes and modulate inflammatory  Functions responses.  With regard to circulating numbers, basophils respond to adrenal  Eosinophils leave the blood when adrenal corticosteroid corticosteroids in similar fashion to eosinophils. hormones increase. They proliferate in response to immunologic  Basophil granules contain histamine, heparin, and peroxidase. stimuli. This proliferative response is mediated, at least with some  Basophils synthesize and store histamine and ECF-A. They antigens, by T lymphocytes, monocytes, and mast cells. synthesize and release slow-reacting substance of  Eosinophils destroy helminths by generating potent oxidants and anaphylaxis (SRS-A) and probably PAF at the time of stimulation releasing cationic proteins (MBP, ECP, Peroxidase). but do not store them.  Eosinophils participate in some inflammatory conditions,  Basophils lack hydrolytic enzymes such as alkaline and acid particularly allergic reactions, asthma, and certain myocardial phosphatase, at least in cytochemically demonstrable amounts. diseases.  Glycogen is abundant outside the granules.  Another major function of eosinophils is to dampen  Although ultrastructurally different, mast cells have similar hypersensitivity and inflammatory reactions. cytochemical characteristics, except for the presence of  Evidence indicates that eosinophils modulate reactions that proteolytic enzymes and serotonin, which basophils lack. In occur when tissue mast cells and basophils degranulate. tissues, the two cell types appear to function in a similar manner.  Eosinophils express the chemokine receptor CCR3.  Basophils (as well as mast cells) appear to be involved in  Among the chemotactic factors that attract eosinophils, immediate hypersensitivity reactions, such as allergic asthma. eosinophil chemotactic factor of anaphylaxis (ECF-A) is  IgE binds readily to basophil and mast cell membranes. When a present in basophils and mast cells; also, eosinophils contain specific antigen reacts with the membrane-bound IgE, 6  degranulation occurs with the release of mediators of  The earliest recognizable cell in this series is the promonocyte, immediate hypersensitivity (e.g., histamine, SRS-A, PAF, which is 15 to 20 μm in diameter, somewhat larger than the heparin, ECF-A). myeloblast.  ECF-A leads to the accumulation of eosinophils, which contain  The N/C ratio is moderate and the nucleus may be oval or substances that tend to counteract these mediators. indented, with a fine uniform or slightly streaked chromatin  Basophils are also involved in some delayed hypersensitivity pattern and two to five nucleoli. reactions, or cutaneous basophil hypersensitivity, such as contact  The cytoplasm is basophilic, with a ground-glass appearance allergies, in which they appear to undergo a different type of and a variable number of fine azurophilic granules. degranulation response.  The monocyte, which is present in both blood and marrow, is only slightly smaller; it has a moderate to low N/C ratio and an indented or lobed nucleus with a finely streaked, only slightly condensed, delicate chromatin pattern.  Nucleoli are indistinct or obscured.  The cytoplasm is opaque, more gray than blue, and contains an abundance of fine azurophilic granules.  Macrophages, the tissue component of the monocyte system, arise from emigrated blood monocytes.  Macrophages are larger than monocytes and measure 15 to 80 μm in diameter. They have irregular cell membranes, often with blebs and pseudopodia.  The N/C ratio is high, with an oblong and/or indented nucleus.  Although macrophages are located in virtually all tissues of the body, the greatest numbers are found in the bowel, liver, bone marrow, and spleen.  In promonocytes, monocytes, and macrophages, the granules contain acid hydrolase, arylsulfatase, nonspecific esterase, and peroxidase. More than one type of granule may be present.  As the cell matures, peroxidase activity diminishes, and acid phosphatase, arylsulfatase, and nonspecific esterase activity Agranulocytes increases. o Agranulocytes lack specific granules but do contain some azurophilic  The enzyme activity occurs in the rough endoplasmic reticulum, granules (lysosomes). Golgi zone, coated vesicles, and digestive vacuoles. This o The nucleus is spherical or indented but not lobulated. This group suggests that, in the macrophages, the coated vesicles are a includes the lymphocytes and monocytes. second form of primary lysosome that shuttles hydrolytic o Monocytes enzymes from the Golgi to the digestive vacuoles.  General descriptions  Functions  Monocytes are precursor cells of macrophages, osteoclasts,  The monocyte is formed in the marrow and transported by the microglia, and other cells of the mononuclear phagocyte system blood. It then migrates into the tissues, where it transforms into in connective tissue of nearly all organs. a histiocyte or a macrophage to spend most of its life span.  Circulating monocytes have diameters of 12-15 μm and have Blood monocytes and tissue macrophages make up a nuclei that are large and usually distinctly indented or C-shaped. mononuclear phagocyte system (reticuloendothelial system).  The chromatin is less condensed than in lymphocytes and  The mononuclear phagocyte system has an important role in typically stains lighter than that of large lymphocytes. defense against microorganisms, including mycobacteria, fungi,  Cells of the mononuclear phagocyte system arise in developing bacteria, protozoa, and viruses. organs from monocytes formed in the embryonic yolk sac and are  The cells are motile and respond to chemotactic factors supplemented throughout life by monocytes from the bone marrow. (complement components as well as lymphokines and γ-  All monocyte-derived cells are antigen-presenting cells with interferon from activated T lymphocytes). important roles in immune defense as well as tissue repair.  They become immobilized by migration-inhibition factor from  The cytoplasm of the monocyte is basophilic and contains many activated lymphocytes. small lysosomal azurophilic granules, some of which are at the  They engage in phagocytosis, a process that is enhanced if the limit of the light microscope’s resolution. particle is coated by IgG or complement for which the  These granules are distributed through the cytoplasm, giving it macrophages have membrane receptors. a bluish-gray color in stained smears.  After phagocytosis, they kill ingested microorganisms.  Mitochondria and small areas of rough ER are present, along  These mononuclear phagocytes are an integral part of both with a Golgi apparatus involved in the formation of lysosomes. humoral and cell-mediated immunity.  After promonocytes are formed, they respond to M-CSF and  They handle or process antigens, providing contact of the undergo 2-3 mitotic divisions in a period of about 50 to 60 hours antigen (or antigenic information) with lymphocytes. before being released into the blood. Under conditions of  They also respond to various lymphokines and monokines and increased demand, the cycle time can shorten, with earlier release act as effector (e.g., cytotoxic) cells in the cell-mediated immune of more immature cells into the blood. response.  Blood monocytes are distributed in a circulating monocyte pool  Monocytes and macrophages function in antibody-dependent and a marginal monocyte pool in a ratio of 1:3.5. cellular cytotoxicity.  Once monocytes enter the blood, they leave randomly with a half-  They have the ability to kill a variety of malignant cells by time of 8.4 hours. This time period is shortened in splenomegaly promoting both cytostasis and cytolysis. or acute infection and may be prolonged in monocytosis.  Some of the ability of macrophages to destroy malignant cells  After monocytes leave the blood, they spend several months, may be attributed to the production of H2O2, nitrous oxide, and perhaps longer, as tissue macrophages. reactive oxygen intermediates.  Morphology  Macrophages remove and process senescent cells and debris  In normal marrow, it is not possible morphologically to distinguish through phagocytosis and digestion. the “monoblast” from the myeloblast.  For example, erythrocytes, leukocytes, and megakaryocyte nuclei are removed by macrophages in the marrow; inhaled 7  particulate material is removed by alveolar macrophages in the  Morphology lungs.  Small lymphocytes have little cytoplasm and, in electron  Macrophages may be activated by specific factors (e.g., micrographs, few organelles and relatively little RNA. cytophilic antibody) or nonspecific factors (e.g., in response to  After antigenic stimulation, small lymphocytes (B cells or T cells, phagocytosed material). depending on the nature of the antigen) become activated,  Activation results in enlargement of the cell and enhanced increase their RNA synthesis, and undergo blast transformation. metabolism, phagocytosis, microbicidal activity, cytotoxicity,  On Romanowsky-stained films, these blasts are large cells (15- secretion of cytolytic proteins (including TNF-α), and the like. 25 μm) with abundant, rather deep-blue cytoplasm, a large  Macrophages synthesize and secrete a large number of reticular nucleus with uniform chromatin, and prominent nucleoli. biologically active molecules, including enzymes, complement This cell is called the reticular lymphocyte (nonleukemic components, binding proteins, coagulation factors, cytokines and lymphoblast; immunoblast). growth factors, chemotactic factors, angiogenesis factors, and  If the blasts are derived from B cells, the new lymphocytes bioactive lipids. function in the production of antibodies (B cells, plasma cells).  Therefore, this system has multiple functions, including host  If the blasts are derived from T cells, the progeny act in cellular defense, control of hematopoiesis, and policing of the immune response. environment within the body.  Atypical lymphocytes are seen in certain viral infections such as o Lymphocytes infectious mononucleosis. These cells have large nuclei with fine  General descriptions chromatin and more abundant cytoplasm that often scallops  By far the most numerous type of agranulocyte in normal blood around adjacent red blood cells. smears, lymphocytes constitute a family of leukocytes with  Large granular lymphocytes contain azurophilic granules in their spherical nuclei. Lymphocytes are typically the smallest cytoplasm; these cells most often represent cytotoxic T cells or NK leukocytes and constitute approximately one-third of these cells. cells.  Although they are morphologically similar, mature lymphocytes  Functions can be subdivided into functional groups by distinctive surface  T cells and their progeny function in cell-mediated immunity, molecules (called “cluster of differentiation” or CD markers) that which includes delayed hypersensitivity, graft rejection, graft- can be distinguished using antibodies with versus-host reactions, defense against intracellular organisms immunocytochemistry or flow cytometry. (such as tubercle bacillus and Brucella), and defense against  Major classes include B lymphocytes, helper and cytotoxic T neoplasms. It is mediated by several soluble factors produced by lymphocytes (CD4+ and CD8+, respectively), and natural the activated T cell: killer (NK) cells. These and other types of lymphocytes have  IL-2- induces the proliferation of T cells diverse roles in immune defenses against invading  IL-3- a multipotential colony-stimulating factor microorganisms and certain parasites or abnormal cells.  IL-4- promotes the proliferation of B cells  T lymphocytes, unlike B cells and all other circulating leukocytes,  IL-5- enhances the proliferation of eosinophils and B cells differentiate outside the bone marrow in the thymus.  IL-6- promotes differentiation of B cells  Although generally small, circulating lymphocytes have a wider  Lymphotoxin- directly toxic to cells range of sizes than most leukocytes.  Migratory inhibitory factor- promotes adherence of  Small, newly released lymphocytes have diameters similar to those of macrophages and keeps them at the site. RBCs; medium and large lymphocytes are 9-18 μm in diameter, with the  B cells and their progeny perform in humoral immunity, or in the latter representing activated lymphocytes or NK cells. production of antibodies, either as a lymphocyte or after  The small lymphocytes are characterized by spherical nuclei with highly transformation into a plasma cell. condensed chromatin and only a thin surrounding rim of scant cytoplasm, o Plasma cells making them easily distinguishable from granulocytes.  Morphology  Larger lymphocytes have larger, slightly indented nuclei and more  Plasma cells have abundant blue cytoplasm, often with light cytoplasm that is slightly basophilic, with a few azurophilic granules, streaks or vacuoles, an eccentric round nucleus, and a well- mitochondria, free polysomes, and other organelles. defined clear (Golgi) zone adjacent to the nucleus.  Lymphocytes vary in life span according to their specific functions;  The nucleus of the plasma cell has heavily clumped chromatin, some live only a few days and others survive in the circulating which is sharply defined from the parachromatin and is often blood or other tissues for many years. arranged in a radial or wheel-like pattern.  A majority of circulating lymphocytes are T cells that have a life  Functions span of months to years. The B cells are a minor population (10%-  Immunoglobulin secreting cells that are derived from activated B- 20% of the lymphocytes), probably have a short life span cells (lineage-switched and mutated), initially as plasmablasts measured in days (with the exception of memory B cells), and are (PB), in both germinal center (GC) and extrafollicular settings. distinguished by the presence of considerable immunoglobulin on  Antibody production and affinity are variable, with a portion of their surface membranes. plasma cells being long-lived. Antibody responses are complex  Lymphocytes circulate in the blood and home to appropriate and vary with antigenic stimuli. lymphoid organs.  During fetal development, lymphocytes migrate from fetal liver to bone marrow or thymus.  Later, pro-T cells migrate from the bone marrow to the thymus, and immature B cells home to secondary lymphoid tissues.  After thymic processing, virgin T cells also home to specific areas in the peripheral lymphoid tissues.  The circulation of lymphocytes is regulated by multiple cell surface adhesion molecules and chemokines, including integrins, selectins, and leukocyte (L) selectin. MEGAKARYOCYTIC (THROMOCYTIC) SERIES  In the postcapillary venule of lymphoid tissue, the lymphocyte travels from the blood through the endothelium and into the General description lymphoid tissue, where it may stay or percolate through and o Platelets originate from polyploid megakaryocytes, the largest of all return to the blood via the thoracic duct lymph. hematopoietic cells, which account for less than 1% of the total nucleated marrow cells. Megakaryocytes arise from megakaryocyte- 8  erythrocyte progenitors (MEP) and then from a megakaryocyte o White Blood Cell (WBC) Differential Count- composed of several precursor (MkP) cell. different types that are differentiated, or distinguised, based on their o Megakaryocyte proliferation is largely regulated by thrombopoietin. size and shape. The cells in a differential count are neutrophils, Additional growth factors, including kit-ligand, IL-3, IL-6, and IL-11, lymphocytes, monocytes, eosinophils, basophils, and bands. support megakaryocytic development in the presence of TPO.  The WBC differential is an evaluation of the types of mature white o Serum TPO levels are generally inversely proportional to platelet count. blood cells in the peripheral circulation. However, levels are elevated in liver disease and inflammatory states,  Although the differential provides only a snapshot of the WBC probably through hepatocyte or marrow stromal cell responses. population at a particular moment in time, it offers valuable o The maturation time for megakaryocytes in the marrow is about 5 days information about an individual’s hematologic status and the in humans. Platelets are released into the marrow sinuses over a individual’s response to any circumstances that may alter that period of several hours, and the megakaryocyte nuclei are status. Generally, the differential is performed on a well-stained, phagocytosed by macrophages. well-distributed peripheral smear. o Newly released platelets appear larger, more active metabolically, and  Relative vs. Absolute Values more effective hemostatically.  Relative and absolute counts refer to the WBC differential. o Platelets circulate at a stable concentration that averages 275 × 109/L.  The absolute count refers to the count derived from the total o At any one time, about two-thirds of the total platelets are in the WBC multiplied by the percentage of any particular WBC. circulation, and the remaining one-third are present in the spleen. In  The relative count refers to the percentage of a particular cell asplenic individuals, all platelets are circulating. counted from the 100 WBC differential. o In diseases characterized by splenic enlargement, 80% to 90% of  An example of how to calculate and interpret the relative and platelets may be sequestered in the spleen, resulting in decreased absolute count follows: concentrations of circulating platelets (thrombocytopenia). o Platelets survive for 8 to 11 days in the circulation. Some platelets are utilized in maintaining vascular integrity and in plugging small vascular injuries (random loss); others are removed by the mononuclear phagocytic system when they become senescent. Morphology o Megakaryocyte development is characterized by endomitosis, nuclear division without cytoplasmic division, which results in ploidies varying from 2N to 64N. Most are 8N and 16N, with smaller numbers on either side. Nuclear lobes do not correlate precisely with ploidy. o Nuclear chromatin is intensely staining, rather dispersed early, and more compact and denser later. o Nucleoli are small at all stages of megakaryocyte development. o The earliest recognizable megakaryoblast has overlapping nuclear lobes and a small amount of basophilic cytoplasm. o Red Blood Cell (RBC) Count- signifies the number of red blood cells  During maturation, nuclear lobes increase and spread out, and red- in a volume of blood pink granules become visible, first in the center of the cell. o Hemoglobin (Hb)- this is the amount of hemoglobin in a volume of o In the mature megakaryocyte, the nucleus is more compact, blood. Hemoglobin is the main component of the RBC and is a basophilia has disappeared, and the granules are clustered into small conjugated protein that serves as the vehicle for the transportation of aggregates. oxygen (O2) and carbon dioxide (CO2) and gives blood its red color. o The formation of individual platelets is a complex process. o Hematocrit (Hct)- is the ratio of the volume of erythrocytes to that of Megakaryocytes develop invaginated surface membranes the whole blood. This is usually measured by spinning down a sample (demarcation membranes) that provide a membrane reserve for of blood in a test tube which causes the RBCs to pack at the bottom proplatelet formation. of the tube. It may be expressed as a percentage (conventional) or in  Proplatelets are pseudopodial extensions of megakaryocytes that L/L (SI units). progressively branch and thin out. Microtubular action is important o Mean Cell (Corpuscular) Volume (MCV)- the average volume of red in the formation of proplatelets and in bringing granule and organelle cells, is calculated from the Hct and the red cell count. It is expressed constituents into the proplatelets. in femtoliters or cubic micrometers  Platelets are formed at the ends of proplatelets and are released by 𝐻𝐻𝐻𝐻𝐻𝐻 (𝐿𝐿/𝐿𝐿) 𝑀𝑀𝑀𝑀𝑀𝑀 = microtubular action. 𝑅𝑅𝑅𝑅𝑅𝑅 (𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚/𝜇𝜇𝜇𝜇) Functions o Mean Cell (Corpuscular) Hemoglobin (MCH)- the content (weight) o Platelets normally function in: of Hb of the average red cell; it is calculated from the Hb concentration  Maintaining the integrity of blood vessels and the red cell count. It is expressed in picograms.  Forming hemostatic plugs to stop blood loss from injured vessels 𝐻𝐻𝐻𝐻 (𝑔𝑔/𝐿𝐿) 𝑀𝑀𝑀𝑀𝑀𝑀 = and, in the process, promoting coagulation of plasma factors. 𝑅𝑅𝑅𝑅𝑅𝑅 (𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚/𝜇𝜇𝜇𝜇) COMPLETE BLOOD COUNT o Mean Cell (Corpuscular) Hemoglobin Concentration (MCHC)- is Definition the average concentration of Hb in a given volume of packed red cells. o The complete blood count (CBC) is one of the most frequently ordered It is calculated from the Hb concentration and the Hct. It is expressed and most time-honored laboratory tests in the hematology laboratory. in g/dL. This evaluation consists of 9 components and offers the clinician 𝐻𝐻𝐻𝐻 (𝑔𝑔/𝐿𝐿) 𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀 = various hematologic data to interpret and review that directly relate to 𝐻𝐻𝐻𝐻𝐻𝐻 (𝐿𝐿/𝐿𝐿) the health of the bone marrow, represented by the numbers and types o Red Cell Distribution Width (RDW)- is a measurement of the of cells in the peripheral circulation. variability of red cell size and shape. Higher numbers indicate greater o The 9 components of the CBC are the white blood cell count (WBC), variation in size. red blood cell count (RBC), hemoglobin (Hgb), hematocrit (Hct), o Platelet count- the number of platelets in a specified volume of blood mean corpuscular volume (MCV), mean corpuscular hemoglobin o Normal values of each component (MCH), mean corpuscular hemoglobin content (MCHC), platelet count, and red blood cell distribution width (RDW). Components o White Blood Cell (WBC) Count- is the number of white blood cells in a volume of blood 9   In the bone marrow, there is a 3 to 4:1 M:E ratio, indicating that 4 myeloid or white cells are produced for 1 erythroid cell.  Daily production of white cells is 1.5 billion. Transit from the bone marrow to the peripheral circulation takes place only after WBCs have been held in the maturation storage pool of the bone marrow.  After being released into the circulation, most WBCs are short- lived before they migrate into tissues. WBCs that are observed in the peripheral circulation are only a snapshot of white cells that are located in three distinct cell compartments: the bone marrow, the bloodstream (circulation), and the tissues.  White blood cells (WBCs) are referred to as leukocytes. For clarity, the word leukocytic applies to the white cells of all stages.  WBCs are a remarkably versatile group of cells whose primary purpose is to defend against bacteria, viruses, fungi or other foreign substances.  To this end, most WBCs are granulated and these granules  Depending on the type of automated instrumentation used, some of contain enzymes used for digestion and destruction of the these parameters are directly read from the instrument and some invading organisms. are calculated. Generally, most automated instruments directly read  Granular leukocytes: Neutrophils, Eosinophils, Basophils the WBC, RBC, Hgb, and MCV. The Hct is a calculated parameter.  Agranular leukocytes: Monocytes, Lymphocytes  Correlation checks between the Hgb and Hct are a significant part  The term granulocytic applies only to granulated white blood of quality assurance for the CBC and are known as “rule of three”. cells. The term myelocytic describes a cell that originated from  The formulas for correlation checks per rule of three are as follows: the myeloid stem cell. The two terms may also be used Hgb x 3 = Hct ± 3 and RBC x 3 = Hgb. interchangeably but only in reference to the leukemias. o Clinical significance of abnormal values  Differential count  Hemoglobin/Hematocrit/RBC count  Because white blood cells have such a short time span in the  Low- anemia peripheral circulation, alterations either in the quantity or in the  High- polycythemia, physiologic variation quality of a particular white blood cell can be quite dramatic.  White cell count  Any increase or decrease in a particular type of cell signals the  White cell counts that are reported on the CBC are directly body’s unique response to “assaults” of any kind. counted from an automated instrument or by manual method.  Infection, inflammation, chronic disease, and parasitic  The age of the patient directly influences whether this number is infestations all are examples of an unexpected occurrence and within or outside the reference range. Pediatric reference ranges an opportunity for white blood cells to mobilize. show more variability than do ranges for adults.  As WBCs respond to infection or other stimuli, changes are seen in the number and types of a particular cell line.  When a cell line is increased, the suffix used to designate an increase is “osis” or “philia” (e.g., “eosinophilia”, “leukocytosis”).  When a cell line is decreased, the suffix used to designate a decrease is “penia” (e.g., “neutropenia”).  Changes are observed in the complete blood count (CBC) and in the peripheral blood smear.  Neutrophilia  Neutrophilic leukocytosis or neutrophilia refers to an absolute concentration of neutrophils in the blood above normal for age.  Key causes are:  Acute inflammatory- collagen vascular, vasculitis  Acute infectious- bacterial, some viral, fungal, parasitic  Drugs, toxins, metabolic- corticosteroids, growth factors, uremia, ketoacidosis  Diurnal variation has been recognized in the neutrophil count,  Tissue necrosis- burns, trauma, MI, RBC hemolysis with highest levels in the afternoon and lowest levels in the  Physiologic- stress, exercise, smoking, pregnancy morning at rest.  Neoplastic- carcinomas, sarcomas, myeloproliferative  Exercise produces leukocytosis, which includes an increased disorders neutrophil concentration as a result of a shift of cells from the  Mechanism: Primary factors influencing neutrophil count are: marginal to the circulating granulocyte pool.  The rate of inflow of cells from the bone marrow  Increased lymphocyte drainage into the blood also appears to (mitosis/proliferation, maturation/storage and release) contribute to the total increase.  The proportion of neutrophils in the marginal granulocyte pool  Both average and lower reference values for neutrophil (MGP; cells adhering to vessel walls) and the circulating concentration in th