Physiology of red blood cells

Physiology of red blood cells.

Flow properties of blood.

Age peculiarities of the blood system.

 

The primary function of blood is to supply oxygen and nutrients as well as constitutional elements to tissues and to remove waste products. Blood also enables hormones and other substances to be transported between tissues and organs. Problems with blood composition or circulation can lead to downstream tissue malfunction. Blood is also involved in maintaining homeostasis by acting as a medium for transferring heat to the skin and by acting as a buffer system for bodily pH.

The blood is circulated through the lungs and body by the pumping action of the heart. The right ventricle pressurizes the blood to send it through the capillaries of the lungs, while the left ventricle re-pressurizes the blood to send it throughout the body. Pressure is essentially lost in the capillaries, hence gravity and especially the actions of skeletal muscles are needed to return the blood to the heart.

Blood is a fluid tissue of human body, classified as a tissue of inner environment. However, its intercellular substance is a liquid, and its cells are not in a fixed position as is the case in other tissues. The blood of adult vertebrates is a red liquid, which circulates in a closed system of tubes, the blood vessels. It is pumped from the heart into arteries, from the arteries into capillaries, and from the capillaries it flows into veins for return to the heart.

Each system of the human body plays an important part in maintaining homeostasis in the internal cellular environment, but the movement of the blood through the circulatory system is of fundamental importance.

The chief function of the blood is to maintaiormal cell function by the constant exchange of nutrients and wasted with all cells.

The blood must also maintain optimum pH and temperature of the intracellular fluid if the cells’ enzyme systems are to work efficiently.The blood transports oxygen from the lungs to the tissues, and carbon dioxide to the lungs for elimination.

 It transport nutrients from the intestine to all parts of the body, and it carries certain waste products to the kidneys for excretion. The blood distributes the heat produced in active muscles and thus aids in the regulation of body temperature.It transports internal secretions from the glands in which they are produced to the tissues on which each exerts its effects.The buffers in the blood help to maintain acid – base balance.The blood also is involved in immunity to disease and in protecting the body against invading bacteria.Blood is divisible into 2 parts, the formed elements and the plasma, in which the formed elements are suspended and in which a variety of important proteins, hormones and other substances are dissolved.

In an average healthy adult, the volume of blood is about one-eleventhof the body weight. Most sources state the volume of blood inan average human adult, who is between 60 -70 kg, as between4.7 and 5 liters, although the more recent sources state the volumeof blood in an average adult as 4.7 liters. Sources state thatan 80-pound child had about half that amount, and an 8-pound infanthas about 8.5 ounces. People who live at high altitudes, wherethe air contains less oxygen, may have up to 1.9 liters more blood than people who live in low altitude regions. The extra blood delivers additional oxygen to body cells. The heart pumps allthe blood in the body each minute when the body is at rest.

 

Functions of the blood review:

1                   Respiratory function (transport of gases: O₂ from the lungs to tissues, CO₂ from tissues to the lungs).

2                   Trophic function (transport of nutrients from gastro-intestinal tract and other organs to all the tissues of the organism).

3                   Excretory function (transport of metabolic products to the excretory organs).

4                   Regulatory function (transport of hormones and biologically active substances from endocrine glands to aim-organs).

5                   Protective function (transport of phagocytes and immunoglobulins).

6                   Thermoregulatory function (transport of heat from organs that maintain warmness – liver and other internal organs to the skin).

Besides, pathogenic factors are transported with blood: microorganisms, toxins, tumor cells. Transport of the last one will lead to the development of metastasis of malignant tumor.

Except the transport function, blood plays an important role in maintaining homeostatic features of the organism. That is why the second important function of the blood is homeostatic function. There are several types of it:

1   Maintenance of the constant chemical content and physical properties of the blood (osmotic pressure, pH, temperature, concentration of ions and other).

2   Maintenance of the constant volume of the circulating blood.

3   Maintenance of the antigenic homeostasis.

The third, important function of the blood is creative function. Macromolecules, which are transported with blood, perform intercellular information transferring, which provides regulation of intracellular processes of protein synthesis, keeping the level of cell differentiation, renovation and maintenance of tissue structure.

 

The cells of blood are of three major functional classes: red blood cells (erythrocytes), white blood cells (leucocytes) and platelets (thrombocytes).

Erythrocytes are primarily involved in oxygen and carbon dioxide transport, the leucocytes constitute an important part of the defense and immune systems of the body, and platelets are a vital component of the blood clotting mechanism. All these cell types are formed in the bone marrow by a process called hemopoiesis. Erythrocytes and platelets function entirely within blood vessels whereas leucocytes act mainly outside blood vessels in the tissues. Thus the leucocytes found in circulating blood are merely in transit between their various sites of activity.

Composition of plasma

Plasma contains 90 % water and 10 % solutes by volume. These solutes include plasma proteins and other organic compounds as well as inorganic salts.

Plasma contains a rich variety of soluble proteins, 7 % by volume. There are three main types: albumins, globulins and fibrinogen. Collectively, the plasma proteins exect a colloidal osmotic pressure within the circulatory system, which helps to regulate the exchange of aqueous solution between plasma and extra cellular fluid.

Albumin – this is the most abundant plasma protein (3,4-5 g/dl of blood) and is mainly responsible for maintaining the osmotic pressure of blood. Substances that are partly or completely water-insoluble (eg, lipids) are transported in the plasma in association with albumin.

The globulins are a diverse group of proteins, which include the antibodies of the immune system, and certain proteins responsible for the transport of lipids and some heavy metal ions.

Alpha, beta, and gamma globulins are globular proteins dissolved in the plasma. The gamma globulins are antibodies and are called immunoglobulins.

Fibrinogen – this protein is converted by blood-borne enzymes into fibrin during clot formation. Fibrinogen is synthesized and secreted by the liver.

Other organic compounds – Other organic molecules in plasma, 2.1 % by volume, include nutrients such as amino acids and glucose, vitamins, and a variety of regulatory peptides, steroid hormones, and lipids.

Inorganic salts in plasma, 0.9 % by volume, include blood electrolytes such as sodium, potassium, and calcium salts.

Blood is studied by spreading a drop on a slide to produce a single layer of cells (blood smear). The cells are stained, differentiated by type, and counted to reveal any disease-related changes in their relative numbers. The smears are usually stained with modifications of dye mixtures containing eosin and methylene blue, ie, Romanovsky-type mixtures.

All of the descriptions of the staining properties of blood cells refer to their appearance after staining with Romanovsky-type mixtures (e.g., Wright’s stain or Giemsa stains). Blood and their components exhibit 4 major staining properties that allow the cell types to be distinguished:

1.                            Basophilia – is an affinity for methylene blue. Basophilic structures stain purple to black.

2.                            Azurophilia – is an affinity for the oxidation products of methylene blue called azures. Azurophilic structures stain red-blue.

3.                            Eosinophilia, or acidophilia, is an affinity for eosin. Eosinophilic structures stain yellow-pink to orange.

4.                            Neutrophilia is an affinity for a complex of dyes (originally thought to be neutral) in the mixture. Neutrophilic structures stain salmon pink to lilac.

The Formed Elements

Erythrocytes, or red blood cells, are the most prevalent cells in peripheral blood. The peripheral blood of an individual contains 25,000,000,000,000 (twenty-five trillion) erythrocytes, and the spleen and bone marrow contain many more.

Each cubic millimeter of blood contains approximately 5 x 106 red cells. The total peripheral blood volume is approximately 5 L. Under normal conditions, these cells never leave the circulatory system. The normal concentration of erythrocytes in blood is approximately 3.9 – 5.5 million per microliter in women and 4.1 – 6 million per microliter in men. A decrease number of erythrocytes in the blood is usually associated with anemia. An increase number of erythrocytes (erythrocytosis) may be a physiologic adaptation – it is found, for example, in people who live at high altitudes, where O2 tension is low. Erythrocytosis, which is often associated with diseases of varying degrees of severity, increases blood viscosity; when severe, it can impair circulation of blood through the capillaries. Erythrocytosis might be better characterized as an increased hematocrit, ie, an increased volume occupied by erythrocytes.

Structure. Most mammalian erythrocytes are biconcave disks without nuclei. When suspended in the isotonic medium, human erythrocytes are 7,5 μm in diameter, 2.6 μm thick at the rim, and 0.8 μm thick in the center. The biconcave shape provides erythrocytes with large surface-to-volume ratio, thus facilitating gas exchange. Erythrocytes with diameters greater than 9 μm are called macrocytes, and those with diameters less than 6 μm are called microcytes. A presence of a high percentage of erythrocytes with great variations in size is called anisocytosis.

 

Scanning electron microscopy of a normal erythrocyte

Normal blood smear

The erythrocytes are quite flexible, a property that permits it to adapt to the irregular shapes and small diameters og capillaries. Observations in vivo show that when traversing the angels of capillary bifurcations, erythrocytes containing normal adult hemoglobin (Hb A) are easily deformed and frequently assume a cup-like shape.

Erythrocytes are surrounded by plasmalemma; because of its ready availability, this is the best-known membrane of any cell. It consists of about 40% lipid, 50% protein and 10% carbohydrates. About half the proteins span the lipid bilayer and are known as integral membrane proteins. Several peripheral proteins are associated with the inner surface of erythrocyte membrane. The peripheral proteins seem to serve as a membrane skeleton that determines the shape of the erythrocyte. They also permit the flexibility of the membrane necessary for the large changes in shape that occur when the erythrocyte passes through capilaries. Because the erythrocytes are not rigid, the viscosity of blood normally remains low.

Mature RBCs lack nuclei and cytoplasmic organelles, which they lose during differentiation. Because they lack mitochondria, the energy needed to maintain the hemoglobin in a functional state must be derived from anaerobic glycolysis. Because they lack ribosomes, the glycolytic enzymes and other important proteins cannot be renewed.

Red blood cells are structurally and functionally specialized to transport oxygen from the lungs to other tissues. Their cytoplasm contains the 33% solution of oxygen-binding protein hemoglobin – the O2 – carrying protein that account for their acidophilia. About 1/3 of the erythrocyte mass is hemoglobin. Each hemoglobin molecule consists of 4 polypeptide subunits, each of which includes an iron-containing heme group.

Hemoglobin (Hb) – is the main erythrocyte compound. It makes 90% of the total solids of the cell. The fact that hemoglobin is kept inside the cell is very important. If hemoglobin was inside the blood plasma, it could cause a number of disorders.

1                    A large amount of free Hb does a toxic influence on different tissues (neurons, kidneys).

2                    In bloodstream Hb is turned to methemoglobin, but in the erythrocyte there are fermentative systems, which predict this to happen.

3                    The amount of hemoglobin, needed for the transport of the enough amount of oxygen will increase stickiness.

4                    Hb will increase an oncotic pressure of plasma that will lead to dehydration of tissues.

5                    The part of Hb will be filtrated through the kidneys and it will choke pores of kidney’s filter.

 

The structure of hemoglobin

Hemoglobin (Hb) – is a red pigment, chromoprotein, which is situated in erythrocytes and transports oxygen.

There is 900 g of hemoglobin in human with body weight 70 kg. There are nearly 400 millions of hemoglobin molecules in one erythrocyte. The molecular mass of hemoglobin is 64 450.

Hemoglobin has globular molecule, which is formed with 4 subunits. Each subunit contains heme. Heme – is Fe-inclusive substance, the derivative of porphyrin. Heme molecule consists of 4 pyrrol. The ion of Fe²⁺ is situated in the center.

                                                                           Deoxygenated hemoglobin                           Oxygenated hemoglobin

 

                                                                          

 

 

Heme is connected with a polypeptide. The complex of polypeptides is called globin part of hemoglobin molecule (globin). There are two pairs of polypeptide chains. Each chain contains more than 140 amino acids. In dependence of number and order of amino acids there are 4 types of chains: α, β, γ, δ (α – 141, β – 146, γ – 146 amino acids) chains, each connected to heme. Heme is disc shaped .

 

                                                                          

 

 

 

 

 

 

                                                                           There are 2α and 2β

 

The main hemoglobin forms and compositions

                                                                           Depending of protein chains there are following forms of hemoglobin iormal state.

·              Hb P (primitive) in embryo for the first 7-12 weeks

·              Hb F (fetal) in fetus. Appears ointh week. Consists of 2α- and 2γ- chains. Hb F can bind and transport oxygen easier (due to lesser similarity HbF to 2,3-BPG). That’s why in the blood of fetus there is enough amount of HbO₂ formed, regardless lower tension of O₂. Normally after birth fetal hemoglobin is changed to adult hemoglobin.

·              HbA₁ (adult). It contains 2α- and 2β- chains. HbA₁ is 95% of all hemoglobin of adult.

·              HbA₂ – it contains 2α and 2δ chains. It is 5% of all hemoglobin of adult.

                                                                           In some inheritable diseases, there are defects of genes, which encode α- or β- chains and the synthesis of Hb is disturbed. These sicknesses are called thalassemias.

                                                                           In α-thalassemia, the synthesis of α-chains is disturbed. Erythrocytes are target-shaped, that’s why α-thalassemia is also called target-shaped anemia. In β-thalassemias synthesis of β-chains is disturbed (Kulee sickness).

                                                                           Defects of the primary structure of hemoglobin also belong to the pathological changes of hemoglobin. Mutative genes, which produce abnormal hemoglobins, are widely spread. There are a lot of forms of abnormal hemoglobins. For example, if glutamate is changed to valine in β-chain, pathological HbS is formed. In deoxygenated state its dissolubility decreases 100 times, and it forms sediment. These crystals deform erythrocyte. Erythrocyte gets sickle-shape, hardly passes through small capillaries and phagocyted by macrophages. It is called sickle-cell anemia.

 

Main physiological compositions of hemoglobin

1)               HbO₂ (oxygemoglobin) is the composition of Hb with oxygen. It has red color, which define the red color of the arterial blood.

                                                                           Due to no oxidation occuring during interaction between Hb and O₂ and oxidation degree of iron does not change; the reaction is called oxygenation (not oxidation).

2)                                                                                                                                                                                   Hb (recovered Hb or deoxy Hb) – Hb, that releases O₂. It has cherry color, which defines the color of the venous blood. Reaction of releasing the oxygen is called deoxygenation.

3)               HbCO₂ (carbhemoglobin) – the composition of Hb with CO₂.

 

                                                                           Pathological composition of Hb:

1)                                                                                                                                                         HbCO (carboxyhemoglobin) – the composition of Hb with CO.

         Chemical relativity of Hb to CO is in 300 times higher than O₂. That’s why carbon monoxide displaces O₂ from hemoglobin, decreasing the ability of the blood to bind oxygen. Even small number of CO leads to the significant increase in formation of HbCO. When concentration of the CO in the air is 0,1% – 80% Hb binds not with O₂, but with CO. When concentration of CO in the air is 1%, in few seconds it will cause death.

                                                                           It is dangerous because HbCO is persistent and Hb cannot transport oxygen anymore.

                                                                           Low intoxication with CO is a reversible process and after breathing fresh air, CO will gradually detach. Breathing with clean oxygen has positive effect.

                                                                           Normally HbCO is 1% of all the Hb. In smokers body it is 3%, after heavy pull – 10%.

2)                                                                                                                                                                                  Met Hb (HbOH – methemoglobin) – hemoglobin, which contains Fe³⁺ and has brown color. Oxidation of Fe²⁺ to Fe³⁺ in hemoglobin occurs when interacting with strong oxidizers (KMnO₄, aniline), and also with medicine of oxidative properties. Insignificant oxidation of hemoglobin to methemoglobin also occurs iormal conditions. But with the help of fermenting systems of erythrocyte (NADH-methemoglobinreductase system) methemoglobin turns in to hemoglobin. Inherited absence of this fermentation can cause inherited methemoglobinemia.

                                                                                       In pathological conditions, when methemoglobin is formed, blood with high oxygen content circulates in the organism, but it is not entering tissues.

                                                                                       The amount of hemoglobin in blood of healthy human is 140-160 g/L for men, 120-140 g/L for women, 200 g/L – for newborns.

 

         Regulation of erythrocyte content in peripheral blood

         The erythrocyte content in peripheral blood of the adult is 3,5 – 5•10¹²/liter. The changes of this value (decrease or increase) can lead to the dangerous changes in human organism. The decrease in the erythrocyte amount leads to the interruption of the oxygen transport in blood, which cause ischemia of organs and tissues. The increase in the erythrocyte amount is the reason of the increase in blood stickiness and the increase of load on heart. When there is essential increase of blood stickiness, the movement of the blood in vessels is impossible.

Regulation of erythrocyte content is provided by regulation of its formation (erythropoiesis) and destruction (haemolysis).

 

Variations iumber of red blood cells

Physiological variations

                    I                        Increase in the red blood cell count is known as poly­cythemia. If it occurs in physiological conditions, it is called physiological polycythemia. It occurs in the following conditions:

1)                Age

At birth, the red blood cell count is 8 -10 millions/cu mm of blood, The count decreases within 10 days after birth due to destruction of cells causing physiological jaundice in some infant.  However, in infants and growing children, the cell count is at a level higher than the value in adults.

2)                Sex

Before puberty and after menopause in females the red blood cell count is similar to that in males. During repro­ductive period of females, the count is less than in males (4.5 millions/cu mm).

3)                High Altitude

The inhabitants of mountains (above 10.000 feet from mean sea level) have an increased red blood cell count of more than 7 millions/cu mm. This is due to hypoxia in high altitude. During hypoxia, the erythropoietin is released from the kidneys. The erythropoietin in turn stimulates the bone marrow to produce more red blood cells.

4)                Muscular Exercise

There is a temporary increase in red blood cell count after exercise. This is because of mild hypoxia and contraction of spleen, which is the reservoir of blood.

5)                Emotional Conditions

The red blood cell count is increased during the emotional conditions like anxiety, because of sympathetic stimula­tion.

6)                Increased Environmental Temperature

The increase in the atmospheric temperature increases red blood cell count.

7)                After Meals

There is a slight increase in the red blood cell count after taking meals.

                 II                        Decrease in red blood cell count occurs in the follow­ing physiological conditions:

1)                High Barometric Pressures

         At high barometric pressures as in deep sea, when the oxygen tension of blood is higher, the red blood cell count decreases.

2)                After Sleep

         The red blood cell count decreases slightly after sleep.

3)                Pregnancy    

In pregnancy, the red blood cell count decreases. This is because of increase in extracellular fluid volume. Increase in extracellular fluid volume, increases the plasma volume also resulting in hemodilution. So, there is a relative reduction in the red blood cell count.

Hematopoiesis

Mature blood cells have a relatively short life span, and consequently the population must be continuously replaced with the progeny of stem cells produced in the hematopoietic organs. In the earliest stages of embryogenesis, blood cells arise from the yolk sac mesoderm. Sometime later, the liver and spleenserve as temporary hematopoietic tissues, but by the second month the clavicle has begun to ossify and begins to develop bone marrowin its core. As the prenatal ossification of the rest of the skeleton accelerates, the bone marrow becomes an increasingly important hematopoietic tissue.

After birth and on into childhood, erythrocytes, granular leukocytes, monocytes, and platelets are derived from stem cells located in bone marrow. The origin and maturation of these cells are termed, respectively, erythropoiesis, granulopoiesis, monocytopoiesis, and megakaryocytopoiesis. The bone marrow also produces cells that migrate to the lymphoid organs, producing the various types of lymphocytes.

Before attaining maturity and being released into the circulation, blood cells go through specific stages of differentiation and maturation. Because these processes are continuous, cells with characteristics that lie between the various stages are frequently encountered in smears of blood or bone marrow.

Stem Cells, Growth Factors, & Differentiation

Stem cells are pluripotential cells capable of self-renewal.

Pluripotential Hematopoietic Stem Cells

It is believed that all blood cells arise from a single type of stem cell in the bone marrow. Because this cell can produce all blood cell types, it is called a pluripotential stem cell. These cells proliferate and form one cell lineage that will become lymphocytes (lymphoid cells) and another lineage that will form the myeloid cells that develop in bone marrow (granulocytes, monocytes, erythrocytes, and megakaryocytes). Early in their development, lymphoid cells migrate from the bone marrow to the thymus, lymph nodes, spleen, and other lymphoid structures, where they proliferate Progenitor & Precursor Cells.

 

 

 

 

 

 

 

 

 

 

 

 

                                                                                        

Stem Cells, Growth Factors, & Differentiation

Stem cells are pluripotential cells capable of self-renewal.

Pluripotential Hematopoietic Stem Cells

It is believed that all blood cells arise from a single type of stem cell in the bone marrow. Because this cell can produce all blood cell types, it is called a pluripotential stem cell. These cells proliferate and form one cell lineage that will become lymphocytes (lymphoid cells) and another lineage that will form the myeloid cells that develop in bone marrow (granulocytes, monocytes, erythrocytes, and megakaryocytes). Early in their development, lymphoid cells migrate from the bone marrow to the thymus, lymph nodes, spleen, and other lymphoid structures, where they proliferate Progenitor & Precursor Cells.

Hematopoiesis is therefore the result of simultaneous, continuous proliferation and differentiation of cells derived from stem cells whose potentiality is reduced as differentiation progresses. This process can be observed in both in vivo and in vitro studies, in which colonies of cells derived from stem cells with various potentialities appear. Colonies derived from a myeloid stem cell can produce erythrocytes, granulocytes, monocytes, and megakaryocytes, all in the same colony.

In these experiments, however, some colonies produce only red blood cells (erythrocytes). Other colonies produce granulocytes and monocytes. Cells forming colonies are called colony-forming cells (CFC) or colony-forming units (CFU). The convention iaming these various cell colonies is to use the initial letter of the cell each colony produces. Thus, MCFC denotes a monocyte-forming colony, ECFC forms erythrocytes, MGCFC forms monocytes and granulocytes, and so on.

Hematopoiesis depends on:

1-Favorable micro-environmental conditions and

2-The presence of growth factors.

Once the necessary environmental conditions are present, the development of blood cells depends on factors that affect cell proliferation and differentiation. These substances are called growth factors, colony-stimulating factors (CSF), or hematopoietins (poietins).

Bone Marrow

Under normal conditions, the production of blood cells by the bone marrow is adjusted to the body’s needs, increasing its activity several-fold in a very short time. Bone marrow is found in the medullary canals of long bones and in the cavities of cancellous bones.Two types of bone marrow have been described based on their appearance on gross examination:

1-red, or hematogenous, bone marrow, whose color is produced by the presence of blood and blood-forming cells; and

2-yellow bone marrow, whose color is produced by the presence of a great number of adipose cells.

Iewborns, all bone marrow is red and is therefore active in the production of blood cells. As the child grows, most of the bone marrow changes gradually into the yellow variety. Under certain conditions, such as severe bleeding or hypoxia, yellow bone marrow is replaced by red bone marrow.

Red Bone Marrow

Red bone marrow (Figure 1) is composed of a stroma (from Greek, meaning bed), hematopoietic cords, and sinusoidal capillaries.

The stroma is a three-dimensional meshwork of reticular cells and a delicate web of reticular fibers containing hematopoietic cells and macrophages. The stroma of bone marrow contains collagen types I and III, fibronectin, laminin, and proteoglycans. Laminin, fibronectin, and another cell-binding substance, hemonectin, interact with cell receptors to bind cells to the stroma.

The sinusoids are formed by a discontinuous layer of endothelial cells.

 

 

 

 

 

 

 

 

 

Section of active bone marrow (red bone marrow) showing some of its components. Five blood sinusoid capillaries containing many erythrocytes are indicated by arrowheads. Note the thinness of the blood capillary wall. Giemsa stain. Medium magnification.

 

 

Maturation of Erythrocytes

A mature cell is one that has differentiated to the stage at which it has the capability of carrying out all its specific functions. The basic process in maturation is the synthesis of hemoglobin and the formation of an enucleated, biconcave, small corpuscle, the erythrocyte. During maturation of the erythrocyte, several major changes take place.

 

These Changes are :

1- Cell volume decreases, and

2- The nucleoli diminish in size until they become invisible in the light microscope.

3- The nuclear diameter decreases, and

4- The chromatin becomes increasingly more dense until the nucleus presents a pyknotic appearance  and is finally extruded from the cell.

5- There is a gradual decrease in the number of polyribosomes (basophilia decreases),

6-  A simultaneous increase in the amount of hemoglobin (an acidophilic protein) within the cytoplasm.

7- Mitochondria and other organelles gradually disappear .

There are three to five intervening cell divisions between the proerythroblast and the mature erythrocyte. The development of an erythrocyte from the first recognizable cell of the series to the release of reticulocytes into the blood takes approximately 7 days.  

The hormone erythropoietin and substances such as iron, folic acid, and cyanocobalamin (vitamin B12) are essential for the production of erythrocytes. Erythropoietin is a glycoprotein produced mainly in the kidneys that stimulates the production of mRNA for globin, the protein component of the hemoglobin molecule.

Differentiation of erythrocytes

The differentiation and maturation of erythrocytes involve the formation (in order) of proerythroblasts, basophilic erythroblasts, polychromatophilic erythroblasts, orthochromatophilic erythroblasts (normoblasts), reticulocytes, and erythrocytes .

1-      Proerythroblastis the first recognizable cell in the erythroid series. It is a large cell with loose, lacy chromatin and clearly visible nucleoli; its cytoplasm is basophilic.

2-      The next stage is represented by the basophilic erythroblast, with a strongly basophilic cytoplasm and a condensed nucleus that has no visible nucleolus. The basophilia of these two cell types is caused by the large number of polyribosomes involved in the synthesis of hemoglobin.

3-      During the next stage, polyribosomes decrease, and areas of the cytoplasm begin to be filled with hemoglobin. At this stage, staining causes several colors to appear in the cell—the polychromatophilicerythroblast.

4-      In the next stage, the nucleus continues to condense and no cytoplasmic basophilia is evident, resulting in a uniformly acidophilic cytoplasm—the orthochromatophilicerythroblast.

5-      At a given moment, this cell puts forth a series of cytoplasmic protrusions and expels its nucleus, encased in a thin layer of cytoplasm. The expelled nucleus is engulfed by macrophages. The remaining cell still has a small number of polyribosomes that, when treated with the dye brilliant cresyl blue, aggregate to form a stained network. This cell is the reticulocyte,

6-      Reticulocyte which soon loses its polyribosomes and becomes a mature erythrocyte.

 

APPENDIX

I.                  Blood plasma content values

 

Inorganic part:

Fe (iron)                         8,53 – 28,06 mkmol/l

K (potassium)                 3,8 – 5,2 mmol/l

Na (sodium)                   138-217 mkmol/l

Ca (calcium)                   0,75 – 2,5 mkmol/l

Mg (magnesium)             0,78 – 0,91 mkmol/l

P (phosphorus)              0,646 – 1,292 mkmol/l

Chlorides of blood         97 – 108 mkmol/l

Filtrate nitrogen (not-protein)    14,28 – 25 mkmol/l

Urea                               3,33 – 8,32 mmol/l

Creatinine                       53 – 106,1 mkmol/l

Creatine                          Men   15,25 – 45,75 mkmol/l

                                      Women       45,75 – 76,25 mkmol/l

Uric acid                        Men   0,12 – 0,38 mkmol/l

                                      Women       0,12 – 0,46 mkmol/l

Organic part:

Total protein                   65 – 85 g/l

Albumins                        35 – 50 g/l

(52 – 65%)

Lactatedehydrogenase (LDH)   < 7 mmol (hour/l)

Aldolase                         0,2 – 1,2 mmol (hour/l)

α-amilase (diastase of blood)    12 – 32 g/l (hour/l)

Aspartateaminotransferase (AST)       0,1 – 0,45 mmol (hour/l)

Alaninaminotransferase (ALT)  0,1 – 0,68 mmol (hour/l)

Cholinesterase                160 – 340 mol (hour/l)

Basic phosphatase          0,5 – 1,3 mmol (hour/l)

Creatinkinase                  0,152–0,305mmol (hour/l)

Creatinphosphokinase (KPK)   to 1,2 mmol

Lipase                            0,4 – 30 mmol (hour/l)

Globulins                       3 – 35 g/l (35 – 48%)

Total bilirubin                 8,5 – 20,5 mkmol/l

free bilirubin

(indirect, not conjugated) 1,7 – 17,11 mkmol/l

conjugated bilirubin (direct)      0,86 – 5,1 mkmol/l

Lipids (total amount)       5 – 7 g/l

Triglicerids                     0,59 – 1,77 mmol/l

Total cholesterol             2,97 – 8,79 mmol/l

Lipoproteins of very low density        1,5 – 2,0 g/l

(0,63 -0,69 mmol/l)

           low density         4,5 g/l

(3,06 – 3,14 mmol/l)

           high density         1,25 – 6,5 g/l

(1,13 – 1,15 mmol/l)

Chylomicrons                 0 – 0,5 g/l

(0 – 0,1 mmol/l)

Glucose of the blood      3,3 – 5,5 mmol/l

Glycolized hemoglobin   4 – 7%

 

II.              Normal Values for Erythrocyte and Leukocyte

Measurements

 

Hemoglobin                                       13–18 g/dL (males);

                                                           12–16 g/dL (females)

Hematocrit                                         42–52% (males);

                                                           37–48% (females)

Erythrocyte count (male)                   4.5–6.0 × 106/mm3

                              (females)              4.0–5.5 ×106/mm3

Leukocyte count                                 5 × 103–10 × 103/mm3

Differential Leukocyte Count

Neutrophils                                         55–75%

Eosinophils                                         2–4%

Basophils                                            0.5–1%

Lymphocytes                                      20–40%

Monocytes                                          3–8%

 

LEUCOCYTES

Leukocytes, or white blood cells, are nucleated and are larger and less numerous than erythrocytes. Leukocytes can be divided into 2 main groups, granulocytes and agranulocytes, according to their content of cytoplasmic granules.

Each of these groups can then be further divided on the basis of size, nuclear morphology, ratio of nuclear to cytoplasmic volume, and staining properties. Two classes of cytoplasmic granules occur in leukocytes, specific and azurophilic granules. Specific granules are found only in granulocytes; their staining properties (neutrophilic, eosinophilic, or basophilic) distinguish the 3 granulocytes types.

Azurophilic granules are found in both agranulocytes and granulocytes. Azurophilic granules stain purple and are lysosomes.

The 5 types of human leukocytes. Neutrophils, eosinophils, and basophils have granules that stain specifically with certain dyes and are called granulocytes. Lymphocytes and monocytes are agranulocytes; they may show azurophilic granules, which are also present in other leukocytes.

 

 

 

Unlike the RBCs, all leukocytes can leave the capillaries by passing between endothelial cells, and penetrating the connective tissue by means of the process called diapedesis. The types and levels of activity expressed by extravascular leukocytes depends upon the specific cell type.

GRANULOCYTES

 

Granulocytes have segmented nuclei and are described as polymorphonuclear leukocytes (PMNLs). Depending on the cell type, the mature nucleus may have from 2 to 7 lobes connected by thin strands of nucleoplasm. Granulocyte types are most easily distinguished by their size and staining properties, and by the appearance (as seen with an electron microscope) of the abundant specific granules in their cytoplasm. These granules are all membrane-limited and bud off the Golgi complex. All granulocytes have a life span of a few days, dying by apoptosis (programmed cell death) in the connoctive tissue. The resulting cellular removed by macrophages and does not elicit an inflamatory response.

 

Neutrophils – are the most abundant leukocytes in the blood. They usually constitute 60-72 % of the white blood cells in healthy adults. They are also found outside the bloodstream, especially in loose connective tissue. Neutrophils are the first line of cellular defense against the invasion of bacteria. Once they leave the bloodstream, they spread out, develop amoeboid motility, and become active phagocytes. Unlike lymphocytes, neutrophils are all terminally differentiated cells and so are incapable of mitosis.

 

Size – neutrophils in the blood are approximately 12 μm in diameter, while those in the tissues spread to a diameter of up to 20 μm.

 

Nucleus – neutrophil nuclei contain highly condensed chromatin both in the lobes and in the attenuated chromatin bridges between them. Most have 3 lobes; however, lobe number increases from a single horseshoe-shaped nucleus in immature neutrophils, called band neutrophils, to more than 5 lobes in aging ones. The nuclei of certain diseased neutrophils, called hypersegmented neutrophils, also have more than 5 lobes (they are typically old cells). In females, a small heterochromatic body often extends from one of the nuclear lobes. This represents the inactive X chromosome, or Barr body, and is referred to as a drumstick – like appendage because of its characteristic shape.

 

Neutrophil cytoplasm is abundant and filled with specific membrane-bound granules. These granules are modified lysosomes and have a bacteriocidal function.

 

Azurophilic granules (primary, or type A) stain with azure dye and are diagnostic for neutrophils. These large (0.4 um) electron-dense granules comprise about 20 % of the granule population and are visible in the light microscope.

 

Specific granules (secondary, or type B) are smaller (0.2 μm) and may contain crystalloids. They comprise 80 % of the granule population and are not visible in the light microscope. They stain salmon pink with typical bloodstains. The less numerous azurophilic granules stain a reddish-purple. The specific granules contain alkaline phosphatase and bactericidal cationic proteins called phagocytins. Azurophilic granules contain lysosomal enzymes and peroxidase. Neutrophils also contain more glycogen than other leukocytes.

 

Neutrophils are short-lived cells with a half-life of 6-7 hours in blood and a life span of 1-4 days in connective tissues, where they die by apoptosis.

 

The primary function of neutrophils is the phagocytosis and destruction of bacteria. Neutrophils are active phagocytes of small particles and have sometimes been called microphages to distinguish them from macrophages, which are larger cells. Neutrophils are inactive and spherical while circulating but change shape upon adhering to a solid substrate, over which they migrate via pseudopodia.

 

Bacteria first adhere to the neutrophil surface and then are surrounded and engulfed by pseudopodia; in this way bacteria eventually occupy vacuoles (phagosomes) delimited by a membrane derived from the cell surface. Immediately thereafter, specific granules fuse with and discharge their contents into the phagosomes. Azurophilic granules then discharge their enzymes into the acid environment, killing and digesting the microorganisms.

The mechanism of phagocytosis

Phagocytosis – is active devourment of the solid substances by cells. Cells, which are capable of phagocytosis, are called phagocytes. There are poly phagocytes (neutrophils) and mononuclear phagotyces (monocytes).

Phagocytes must be selective of the material that is phagocytized; otherwise, normal cells and structures of the body might be ingested. Whether phagocytosis will occur, depends especially on three selective procedures. Firstly, most natural structures in the tissues have smooth surfaces, which resist phagocytosis. But if the surface is rough, the likelihood of phagocytosis is increased. Secondly, most natural substances of the body have protective protein coats that repel the phagocytes. Conversely, most dead tissues and foreign particles have no protective coats, which make them subject to phagocytosis. Thirdly, the immune system of the body develops antibodies against infectious agents such as bacteria. The antibodies then adhere to the bacterial membranes and thereby make the bacteria especially susceptible to phagocytosis. To do this, the antibody molecule also combines with the C3 product of the complement cascade, which is an additional part of the immune system discussed in the next chapter. The C3 molecules, in turn, attach to receptors on the phagocytic membrane, thus initiating phagocytosis. This selection and phagocytosis process is called opsonization.

 

Stages of phagocytosis:

                    I                                                                                                                                                                         Conjugation stage. Phagocyte moves to direction of not self agent (chemotaxis).

                 II                                                                                                                                                                         Adhesion stage. Phagocyte interacts with the agent. There are two mechanisms:

1)                                                                                                                                                                 without receptor: electrostatic and hydrophobic interaction (phagocyte is negatively charged, positive particles);

2)                                                                                                                                                                 with receptor. On the surface of macrophages there are receptors for opsonin-substances that can interact with bacteria.

             III                                                                                                                                                                         Devourment stage. Its steps:

·                                                                                                                                                                    invagination of phagocyte membrane on the contact place;

·                                                                                                                                                                    the formation of phagosome, which contains the agent;

·                                                                                                                                                                    the formation of phagolysosome: consolidation of phagosome with lysosomes (secondary granules).

              IV                                                                                                                                                                         Digestive stage. Its steps:

·                                                                                                                                                                    The disposal of bacteria – intercellular cytolysis with the help of germicide systems of phagocytes (myeloperoxidase system, which produces hypochloride ion ClO^–, free radicals and peroxides O³⁰, HO²⁰, OH⁰, lisocim, lactoferin, non-enzymatic cationic proteins, lactic acid).

·                                                                                                                                                                    Digestion – hydrolysis of killed bacteria with the help of hydrolytic enzymes.

 

 

Eosinophils – constitute only 0,5-54 % of the circulating leukocytes in healhty adults. They may leave the bloodstream by diapedesis, spread out, and move about in the connective tissues. They are capable of only limited phagocytosis, showing a preference for antigen-antibody complexes. The number of circulating eosinophils typically increases (eosinophilia) during allergic reactions and in response to parasitic (helmintic) infections, and rapidly decreases in response to treatment with exogenous corticosteroids. These cells produce substances that modulate inflammation by inactivating the leukotriens and histamine produced by other cells.

Eosinophil nuclei contain condensed chromatin and usually have 2-3 lobes connected by a thin chromatin bridge (bilobed nucleus). The nuclei are often partially obscured by the numerous specific granules in the cytoplasm.

 

Cytoplasm – The most characteristic structural feature of eosinophils is the presence of numerous large (0.5-1.5 μm in diameter), brightly eosinophilic granules (specific granules) in their cytoplasm (about 200 per cell). These granules are specialized lysosomes that lack lysozyme but contain acid phosphatase, cathepsin, and ribonuclease. In electron micrographs, each specific granule has an oblong shape and an elongated, centrally located, electron-dense crystalloid, or internum, lying parallel to its long axis. It contains a protein called the major basic protein – with a large number of arginine residues. This protein constitutes 50% of the total granule protein and accounts for the eosiniphilia of these granules. The major basic protein also seems to function in the killing of parasitic worms such as schistosomes. Between the granule membrane and the internum lies the electron-lucent matrix, or externum. Microfilaments are prominent in the eosinophil cortex.

 

Functions. Eosinophils kill parasitic larvae as they enter peripheral blood or the lamina propria of the gut. They help to regulate mast cell response to inflammation by releasing an enzyme that degrades the histamines released by mast cells at inflammation sites. Eosinophilic granule crystalloids have a dominant component called the major basic protein, which has a poorly understood antiparasitic function. Eosinophilic granules contain lysosomal enzymes that destroy dead parasites.

 

Basophils are the least numerous of the circulating leukocytes, constituting from 0 to 1% of the white blood cells of healthy adults. Like other white blood cells, basophils may leave the circulation, but they are capable of only very limited ameboid movement and phagocytosis in the tissues. Extravascular basophils are most often found at sites of inflammation and may be the major cell type at sites of cutaneous basophil hypersensitivity.

Basophils vary in diameter from 12 μm to 15 μm but are usually slightly smaller thaeutrophils. Their nuclei are less heterochromatic than other granulocytes and usually consist of 3 irregular lobes which are often obscured by the large, dark-staining cytoplasmic granules. The specific granules of basophils are their most characteristic feature. These granules have irregular shapes and vary in size; the largest are the size of the specific granules of eosinophils, the smallest nearly as small as those of neutrophils. The granules stain metachromatically and appear reddish-violet to nearly black in stained blood smears. The specific granules of basophils (like those of the mast cells of connective tissue) contain heparin and histamine, which may be released by exocytosis in response to certain types of antigenic stimuli. The granules may contain inclusions, but they appear more homogeneously electron-dense than do those of eosinophils.

Functions. Basophils mediate the inflammatory response and secrete eosinophil chemotactic factor. In response to certain antigens, basophils stimulate the formation of immunoglobulin E(IgE)-a class of antibodies. Subsequent exposure to the same antigen can cause a basophil and mast cell response restricted to specific organs (e.g., bronchial asthma in the lungs or a severe and systemic response such as anaphylactic shock brought on by a bee sting).

 

Agranulocytes

 

Agranulocytes have round unsegmented nuclei and are described as mononuclear leukocytes. They lack specific granules, but they contain various number of azurophilic granules (lysosomes) that bind the azure dies of the stain. This group includes the lymphocytes and monocytes.

Lymphocytes – constitute a diverse class of cells; they have similar morphologic characteristics but a variety of highly specific functions. They normally account for 20-25 % of the white blood cells in adult blood, with a considerable range of normal variation (20-45%). Lymphocytes are also found outside the blood vessels, grouped in lymphatic organs or dispersed in connective tissues. They respond to invasion of the body by foreign substances and organisms and assist in their inactivation. They also have diverse functional roles, all related to immune reactions in defending against invading microorganisms, foreign macromolecules and cancer cells. Unlike other leukocytes, lymphocytes never become phagocytic.

They can be classified into several groups due to distinctive surface molecules (markers), which can be distinguished only by immunocytochemical methods.

 

The 2 major functional classes of lymphocytes are T cells and B cells. Lymphocytes in the blood are predominantly (about 80 %) T cells.

Lymphocytes vary from 6 to 18 μm in diameter. Most of those found in blood are small lymphocytes in the 6- to 8 μm range, making them the smallest leukocytes, comparable in size to erythrocytes. A small number of medium-sized and large lymphocytes are also ground in the circulation and probably represent lymphocytes activated by an antigen.

 

Lymphocyte nuclei are spheric and often flattened on one side. In small lymphocytes, the nucleus is densely heterochromatic, staining purplish-blue to black, and nearly fills the cell. In large lymphocytes, the nucleus is larger and less dense and stains reddish-purple.

 

Lymphocyte cytoplasm exhibits a pale basophilia and occasionally contains a few purplish azurophilic granules but lacks specific granules. In the smaller cells, the cytoplasm forms a thin rim around the nucleus; in the larger cells, it is more abundant. It contains many free ribosomes, few mitochondria, sparse endoplasmic reticulum, and a small Golgi complex. When stimulated by an antigen, lymphocytes undergo blast transformation, a process of enlargement and sequential mitotic divisions. Some of the daughter cells, called memory cells, return to an inactive state but retain the capacity to respond more quickly to the next encounter with the same antigen. Other daughter cells, called effector cells, become activated to carry out an immune response to the antigen. Effector cells may be derived from either B lymphocytes (B cells) or T lymphocytes (T cells). While circulating B and T cells are morphologically indistingushable, they carry different cell-surface components (antigens recognized by other species) and can be identified by special procedures.

 

B Lymphocytes differentiate into plasma cells, which secrete specific antigen-binding molecules (antibodies or immunoglobulins) that circulate in the blood and lymph and serve as a major component of humoral immunity.

 

T Lymphocyte derivatives serve as the major cells of the cellular immune response. They produce a variety of factors, termed lymphokines (eg, interferon) that influence the activities of macrophages and of other leukocytes involved in an ammune response. There are several types:

(i)                Cytotoxic (killer) cells secrete substances that kill other cells and in some cases kill by direct contact; they play the major role in graft rejection.

(ii)              Helper T cells enhance the activity of some B cells and other T cells.

(iii)            Suppressor T cells inhibit the activity of some B cells and other T cells.

The primary (central) lymphoid organs include the thymus, where lymphocyte precursors are programmed to become T cells and, in birds, the bursa of Fabricius, where lymphocyte precursors are programmed to become B cells. Humans have no bursa; our B cells appear to be programmed in the bone marrow.

         According to the electron-microscopic studies there are 4 different types:

1.     Small dark lymphocytes;

2.     Small light lymphocytes;

3.     Medium lymphocytes;

4.     Plasmocytes or lymphoplasmocytes.

         Lymphocytes vary in life span; some live only a few days, and others survive in the circulating blood for many years. Lymphocytes are the only type of leukocytes that return from tissue back to the blood, after diapedesis.

 

 

Monocytes are often confused with large lymphocytes, but they are larger and constitute only 3-8 % of the white blood cells in healthy adults. Monocytes are found only in the blood, but they remain in circulation for less than a week before migrating through capillary walls to enter other tissues or to become incorporated in the lining of sinuses. Once outside the bloodstream, they become phagocytic and apparently do not recirculate. Monocytes are the direct precursors to macrophages. The mononuclear phagocyte system (portions of which  were formerly referred to as the reticuloendothelial system) consists of monocyte-derived phagocytic cells distributed throughout the body. Examples include the Kupffer cells of the liver and some of the macrophages of connective tissues.

Monocytes in the blood of healthy adults have a diameter of 12-15 μm, but when they attach to surfaces they flatten and spread out, often reaching 20 μm in diameter they are the largest among leukocytes).

 

Monocyte nuclei may be ovoid, but are usually kidney- or horseshoe shaped and eccentrically placed; unlike lymphocyte nuclei, they are rarely spherical. The chromatin is less condensed than that of lymphocyte nuclei, has a “smudgy” appearance, and stains reddish-purple. There may be 2-3 nucleoli, but these are often difficult to distinguish.

Cytoplasm – The faint blue-gray cytoplasm of monocytes is more abundant than that of lymphocytes and contains many small azurophilic granules, which are distributed through the cytoplasm, giving it a bluish-gray color in stained smears. In the lectrone microscope, one or two nucleoli are seen in the nucleus, and a small quantity of rough endoplasmic reticulum, polyribosomes. It also contains many small mitochondria, a well-developed Golgi apparatus. Many microvilli and pinocytotic vesicles are found at the cell surface.

 

An increase in the number of leukocytes is called leukocytosis; this occurs in most systemic and localized infectious processes, such as appendicitis or abscesses. It is a normal response to infection. On the other hand, a decrease in the number of leukocytes is called leukopenia; this may occur in certain acute and chronic diseases, such as typhoid fever or tuberculosis. Leukopenia is also a constant finding in radiation sickness, the clinical result of excessive exposure to gamma rays. For example, victims of the atomic bomb expositions were exposed to intensive radiation and as result suffered a marked depression of bone marrow function; the absolute white count in the more severe cases ranged from 1500 to zero per cu. mm. of blood. There also was anemia, due to interference with formation of red blood cells.

Life of white blood cells

Lifespan of white blood cells are not constant. It depends upon the demand in the body and their function. Lifespan of these ceils may be as short as half a day or it may be as long as 3-6 months. However, the normai lifespan of white biood cells is as follows:

Neutrophils     —    2-5 days

Eosinophils     —    7-12 days

Basophils      —     12-15 days

Monocytes     —    2-5 days

Lymphocytes   —    ¹/₂-1 day

The amount in peripheral blood – 4-9 · 10⁹/liter.

The decrease of leucocytes amount is called leucopenia, the increase – leucocytosis.

There are 2 types of leucocytes:

 

                 V                                                                   Physiological – is normal, physiological reaction of the organism in some irritations. There are following types, dependently on their causes:

1)                emotional leucocytosis (occurs in result of emotional stresses);

2)                 myogenic (occurs in result of intensive physical exercises);

3)                 static (occurs in result of change of the position of the human body from horizontal to vertical);

4)                 alimental (occurs during or after eating);

5)                 painful (occurs during strong painful feelings);

6)                 leucocytosis of pregnant;

7)                 leucocytosis of newborn.

 

II       Pathological (reactive) – it is connected with the pathological process in the organism. Its reasons:

1)                infectious diseases;

2)                inflammatory processes;

3)                allergic reactions;

4)                intoxications of endo- and exogenous origin.

 

The difference between physiological

and reactive leucocytosis

 

Physiological leucocytosis:

1) it is redistributing (leucocytes from the parietal pool are moving into circulation);

2) it has transient character (it is normalizing fast after the cause disappears);

3) leukogram does not change (the correlation between different forms persists);

4) degenerative forms of leucocytes do not appear.

 

Reactive leucocytosis is connected with the increase of proliferation and maturating of leucocytes in red bone marrow or increase of moving of reserve leucocytes from RBM to the blood. During pathological leucocytosis the correlation between different forms of leucocytes is disturbed.

Percentage ratio between different forms of leucocytes is called leukogram (formula of Arnet-Shilling).

 

 

 

Differential white blood cell count (Differential leukocyte count)

 

Physiological values of leukocyte count: 5-10 x 10⁹/L blood

Neutrophil granulocytes

Physiological values: 2-7.5 x 10⁹/l (60-70%)

Increased number – neutrophilia: bacterial infections, trauma, scorch, bleeding, inflamations, infarction, polymialgy, myeloproliferative disorders, reaction to certain medications (e.g. chorticosteroides). Significantly increased in leukemia, disseminated malignant diseases and complicated childhood infections.

Decreased number – neuthropenia: viral infections, brucellosis, thyphoid, Kala-azar, TBC, sepsis, lupus erithematodes, rheumatoid arthritis, avitaminosis B12  i bone marrow dissorders. Medications like carbamazepine or sulphonamides can decrease a number of neuthrophils. 

Band neutrophils (stab neutrophils) cells are younger forms of cells presented with kidney-shape, curved nucleus and not segmented, lobar nucleus. Usually they are represent 3-5% of leukocytes. Increased value indicates a higher demand and expenditure of neutrophils, and is called “left shift” (referring to ratio of immature to mature forms of neutrophils).

Lymphocytes

Physiological values: 1.3-3.5 x 10⁹/l (20-40%).

Increased number – lymphocytosis: viral infections (EBV-Epstein Barr virus, CMV-cytomegalovirus, rubeola), toxoplasmosis, pertusis, brucellosis, chronic lymphatic leukemia.

Decreased number – lymphopenia: corticosteroid treatment, lupus erithematodes, uremia, legionella disease, AIDS, bone  marrow infiltration (tumor), after chemotherapy and radiotherapy.

Subclases: CD4: 537-1571/mm3 (decreased in HIV infection); CD8: 235-753/mm3; CD4/CD8 ratio: 1.2-3.8.

 

Eosinophil granulocytes

Physiological values: 0.04-0.44 x 10⁹/l (1-4%).

Increased number – eosinophilia: asthma i allergic disease, parasitic infestations, skin diseases (especially pemphigus), urticaria, egzema, malignant diseases (including eosinophilic leukemia), irradiation, Loeffler syndrome, recovery after infections. Hypereosinophilic syndromecan be observed in terminal organ damage (restrictive cardiomyopathy, neuropathy, hepatosplenomegaly), withincreased eosinophile number for more than 6 weeks (>1.5 x 10⁹/l).

Eosinophilia-myalgi syndrome – muscle pain (myalgia), joint pain (arthralgia), increased body temperature, rash, arms swelling and intense eosinophilia.

Monocytes

Physiological values: 0.2-0.8 x 10⁹/l (2-6%).

Increased number – monocytosis: acute and chronic infection (TBC, brucellosis, protozoal infections), malignant diseases (acute myeloid leukemia, Hodgkin lymphoma), myelodisplasia.

Basophil granulocytes

Physiological values: 0.01 x 10⁹/l (0.5-1%).

Increased number – basophilia: viral infections, urticaria, myxedema, after splenectomy, chronic myeloid leukemia, malignant disease, systemic mastocytosis (urticaria pigmentosa), hemolysis, policitemia rubra vera.

 

Production of leucocytes

Granulopoiesis

The maturation process of granulocytes takes place with cytoplasmic changes characterized by the synthesis of a number of proteins that are packed in two organelles: the azurophilic and specific granules. These proteins are produced in the rough endoplasmic reticulum and the Golgi complex in two successive stages. The first stage results in the production of the azurophilic granules. In the second stage, a change in synthetic activity takes place with the production of several proteins that are packed in the specific granules. These granules contain different proteins in each of the three types of granulocytes and are utilized for the various activities of each type of granulocyte.

Maturation of Granulocytes

The myeloblast is the most immature recognizable cell in the myeloid series. It has a finely dispersed chromatin, and nucleoli can be seen. In the next stage, the promyelocyte is characterized by its basophilic cytoplasm and azurophilic granules. These granules contain lysosomal enzymes and myeloperoxidase.

The promyelocyte gives rise to the three known types of granulocyte. The first sign of differentiation appears in the myelocytes, in which specific granules gradually increase in quantity and eventually occupy most of the cytoplasm. These neutrophilic, basophilic, and eosinophilic myelocytes mature with further condensation of the nucleus and a considerable increase in their specific granule content.

Kinetics of Neutrophil Production

The total time taken for a myeloblast to emerge as a mature neutrophil in the circulation is about 11 days. Under normal circumstances, five mitotic divisions occur in the myeloblast, promyelocyte, and neutrophilic myelocyte stages of development.

Neutrophils pass through several functionally and anatomically defined compartments:

1-      The medullary formation compartment can be subdivided into a mitotic compartment (≈3 days) and a maturation compartment (≈4 days).

2-      A medullary storage compartment. Neutrophils remain in this compartment for about 4 days.

3-      The circulating compartment consists of neutrophils suspended in plasma and circulating in blood vessels.

4-      The marginating compartment is composed of neutrophils that are present in blood but do not circulate. These neutrophils are in capillaries and are temporarily excluded from the circulation by vasoconstriction, or—especially in the lungs—they may be at the periphery of vessels, adhering to the endothelium, and not in the main bloodstream.

The marginating and circulating compartments are of about equal size, and there is a constant interchange of cells between them. The half-life of a neutrophil in these two compartments is 6–7 h. The medullary formation and storage compartments together are about 10 times as large as the circulating and marginating compartments.

Neutrophils and other granulocytes enter the connective tissues by passing through intercellular junctions found between endothelial cells of capillaries and postcapillary venules (diapedesis). The connective tissues form a fifth compartment for neutrophils, but its size is not known. Neutrophils reside here for 1–4 days and then die by apoptosis, regardless of whether they have performed their major function of phagocytosis.

Maturation of Lymphocytes & Monocytes

Study of the precursor cells of lymphocytes and monocytes is difficult, because these cells do not contain specific cytoplasmic granules or nuclear lobulation, both of which facilitate the distinction between young and mature forms of granulocytes. Lymphocytes and monocytes are distinguished mainly on the basis of size, chromatin structure, and the presence of nucleoli in smear preparations.

Lymphocytes

Circulating lymphocytes originate mainly in the thymus and the peripheral lymphoid organs (eg, spleen, lymph nodes, tonsils). However, all lymphocyte progenitor cells originate in the bone marrow. Some of these lymphocytes migrate to the thymus, where they acquire the full attributes of T lymphocytes. Subsequently, T lymphocytes populate specific regions of peripheral lymphoid organs. Other bone marrow lymphocytes differentiate into B lymphocytes in the bone marrow and then migrate to peripheral lymphoid organs, where they inhabit and multiply in their own special compartments.

The first identifiable progenitor of lymphoid cells is the lymphoblast, dividing two or three times to form prolymphocytes.

Monocytes

The monoblast is a committed progenitor cell that is almost identical to the myeloblast in its morphological characteristics. Further differentiation leads to the promonocyte, a large cell (up to 18 µm in diameter) with a basophilic cytoplasm and a large, slightly indented nucleus. The chromatin is lacy, and nucleoli are evident. Promonocytes divide twice in the course of their development into monocytes. A large amount of rough endoplasmic reticulum is present, as is an extensive Golgi complex in which granule condensation can be seen to be taking place. These granules are primary lysosomes, which are observed as fine azurophilic granules in blood monocytes. Mature monocytes enter the bloodstream, circulate for about 8 h, and then enter the connective tissues, where they mature into macrophages and function for several months.

 

 

IMMUNITY

 

The body is under constant attack by micro-organisms. They may enter the body via an orifice eg mouth nasal passage or vagina, or through broken skin. The micro –organisms feed on the body tissues and /or pass toxins into the bloodstream. This causes disease. Disease causing organisms are called pathogenic. Inside the body the micro-organism has ideal conditions of food, water and temperature, so flourish.

Immunity is the body’s ability to resist infection by a disease-causing organism (pathogen) or to destroy it after invasion.

Immunity can be innate or acquired.

Innate immunity.

This is inborn and unchanging and occurs in several non-specific ways.

1. Skin. This is an effective physical barrier

2. Stomach acid. This destroys the protein membrane of any invading mico-organism.

3.Lysozyme. An enzyme found in tears, saliva and nasal secretions which digests bacterial cell walls

4. Interferon. This is released by an infected cell , binds to a non-invaded cell inducing it to produce antiviral proteins in readiness for invasion.

5. Phagocytosis. Some types of white blood cells engulf invading  bacterial cells and digest them using enzymes enclosed in lysosomes ( diagram P 50)

Phagocytic white blood cells, monocytes, and macrophages derived from monocytes, are produced in the bone marrow. They are found static or fixed in the lining of tubules in the liver, spleen and lymph nodes, and remove pathogens as  blood or lymph passes by. Pus at an infected wound is the remains of dead pathogens and phagocytic white blood cells.

 

Acquired immunity

 

This type of immunity is acquired throughout a lifetime, and depends on the production of special protein molecules called antibodies. These antibodies are produced in response to specific foreign molecules called antigens.

An antigen is a polysaccharide or protein which is recognised as foreign by special white blood cells, lymphocytes. These lymphocytes respond by producing specific antibodies for that antigen.

 

An antibody is a Y shaped protein which has specific receptor or binding sites on each arm.

 

There are thousands of different lymphocytes each capable of responding to a specific antigen and producing a specific antibody.

 

Acquired immunity can be developed either naturally or artificially.

 

Naturally acquired immunity.

 

This occurs when the body suffers an infection.

Lymphocytes are derived from unspecialised cells in the bone marrow. On production some of these cells migrate to the thymus gland and the lymph nodes where they reproduce to form colonies.

Thymus lymphocytes are called T lymphocytes or T cells. Those from the lymph nodes are called B cells.

 

B cell action.  Humoral response, the release of free antibodies.

 

When a B cell encounters an antigen it divides repeatedly to produce identical daughter cells, which make and release the specific antibody for that antigen. In the blood or lymph these antigens bind with the antigen to form an antigen/antibody complex. This acts as a signal for phagocytic white blood cells to engulf and destroy the whole complex.

Some of the activated B cells remain in the body fluids as memory cells, and continue to produce the antibody. This means that on further infection by the same antigen many antibodies can be released very quickly reducing response time.

 

(Antibodies or immunoglobulins are proteins that are able to act against what they recognise as foreign (antigens). There are 5 major classes of immunoglobulin, IgA,IgD ,IgG IgM and IgE. IgG is the only one that can cross the placenta, and food or environmental allergies involve IgA, IgM and IgE.)

 

T cell action. Cell mediated response.

 

On invasion of a body cell by a micro-organism, microbial proteins are released. These move to the body cell membrane and act as antigens. The antigens are recognised as foreign by Killer –T cells. The killer T cells attach to the infected body cell releasing chemicals, which perforate the body cell membrane. This destroys the body cell and the micro-organisms inside.

 

Another type of T cell , Helper T cells do not kill the cells but act as ’lookouts’ by patrolling the body, recognising antigens and activating B cells and Killer T cells.

 

Primary and Secondary responses.

 

After invasion by a micro-organism the individual will suffer the disease until there are sufficient antibodies produced. This is the primary response. If the individual is infected by the same micro-organism, memory B cells in the body will quickly produce many antibodies, and memory killer T cells will attack the infected cells, so the response is much faster preventing the disease. This is the secondary response.

 

Artificially acquired immunity.

 

Inoculation. This is the deliberate introduction of an antigen into the body to stimulate an immune response.

Vaccination is a form of inoculation, where the antigen is introduced either by injection or orally. The antigen is first rendered harmless by heat or chemical treatment but will still induce an immune response by production of B and T cells. Treated micro-organism toxins can also be used in this way.

 

 

Blood Group Systems

Blood is grouped on the basis of the type of aggluti­nogen present on its erythrocytes. Thus, blood group A has A agglutinogen on its erythrocytes while blood group M has agglutinogen-M on its erythrocytes. All blood groups obey, in whole or in part, Landsteiner’s law which states that: (1) when the blood contains a particular agglutinogen, its corresponding agglutinin is always absent in that blood, and (2) when a particular agglutinogen is absent in the blood, its correspond­ing agglutinin is always present in the blood. The first clause of the law is always true but the second clause is valid only for the ABO blood groups.

While innumerable agglutinogens have been de­ciphered in the blood, the important ones are those which are widely prevalent in the population and those which cause the worst transfusion reactions. These are called the major blood group systems, e.g., the ABO and the Rhesus (CDE) systems. Some blood groups are found only in a small proportion of the population and occasionally produce mild transfusion reactions. These are called the minor blood group systems, e.g., MN, P, etc. In addition to the major and minor blood groups, there are familial blood groups such as the Kell, Duffy, Diego, Lewis, Lutheran, Kidd, and many others that are named after individuals, mostly women, whose blood groups were detected during childbirth. These blood agglutinogens are prevalent only in a few families.

The ABO system comprises two agglutinogens A and B whose corresponding agglutinins are α and β. Ac­cordingly, there are 4 blood groups in the ABO system: Group A, which has A agglutinogen, group B which has B agglutinogen, group AB having both, and group O hav­ing neither. Group A has α agglutinin, group B has β agglutinin, group AB has neither, and group O has both  Both α and β agglutinins are immunoglob­ulin-M (IgM), which is very effective in causing aggluti­nation (clumping) of the red cells.

In India, about 22% of the population have A group, 33% have B group and 40% have O group blood. Only 5% have AB group blood. 85% of Caucasians are D+. Among Asians, over 99% are D+.

The Rhesus blood group agglutinogens were first dis­covered in the erythrocytes of rhesus monkeys, and hence the name. Rhesus blood group comprises a sys­tem of 3 agglutinogens: C, D, and E. However, for all practical purposes, the term Rhesus agglutinogen re­fers to the D agglutinogen which produces the worst transfusion reactions. Accordingly, the Rhesus system comprises only two blood groups: the Rhesus positive (Rh positive or D+) and the Rhesus negative (Rh nega­tive or D–) blood groups depending on the presence or absence of D agglutinogen

Unlike in the ABO system, there are no natural an­tibodies to rhesus agglutinogens. Anti-D antibodies develop only when a D– person is transfused with D+ blood. Once produced, these antibodies persist in blood for years and can produce serious reactions dur­ing a second transfusion.

Anti-D agglutinins are predominantly immuno­globulin G (IgG) and partly immunoglobulin M (IgM ). Unlike IgM which is very effective in agglutinating ag­glutinogen-bearing red cells, IgG does not agglutinate the red cells although they do react with the agglutinin. Such immunoglobulins which do not cause agglutina­tion are called incomplete antibodies. Although they do not agglutinate red cells, IgG-coated red cells still get lysed due to the activation of complement on their sur­face

Blood grouping

For ABO blood grouping, the test sample of blood or erythrocyte suspension is reacted with sera contain­ing α and β (called antiserum-A and antiserum-B). The sample is grouped according to the serum that aggluti­nates its red cells.

Rhesus blood grouping can be done in the same way as ABO grouping if the anti-D agglutinin used is of the IgM type. If the anti-D agglutinin used is IgG, the D+ red cells will get coated with anti-D agglutinin but there will be no agglutination of the cells. The coated red cells will agglutinate only on subsequent addition of Coombs’ (anti-immunoglobulin) serum .

Agglutination will also occur if the IgG anti-D is poten­tiated by adding albumin to it.

Genotypes and inheritance

The ABO phenotypes are controlled by a pair of codomi­nant alleles A and B. An individual who has inherited A-agglutinogen from one parent and B agglutinogen from the other parent will have the AB blood group. Similarly, an individual whose phenotypic blood group is B may have either the genotype BB (homozygous) or BO (heterozygous).

The Rh phenotypes are controlled by three sets (C, D, and E) of two alternative alleles (dominant and reces­sive). Each phenotype has a variable number of pos­sible genotypes. For example, cde has only one possible genotype, i.e., ccddee. CDE on the other hand can have eight possible genotypes, viz., CCDDEE, CCDDEe, CCD­dEE, CCDdEe, CcDDEE, CcDDEe, CcDdEE, and CcDdEe.

 

Agglutinogens and agglutinins

The ABO agglutinogens represent only a few of the ap­proximately one million agglutinogens present on an erythrocyte. The ABO agglutinogens are glycosphingo­lipids (oligosaccharide plus sphingolipid). The antigenicity of the agglutinogens resides in the oligosaccharide moiety. The ABO agglutinogens are present on the red cell membrane as peripheral proteins. O group cells contain a non-antigenic H substance from which both A and B agglutinogens are derived. The genes for A and B agglutinogens are located on chromosome 9. They code the synthesis of transferase-A and transferase-B, the two enzymes that are responsible for conversion of substance H into A and B agglutinogens.

ABO agglutinogens are not confined to erythrocytes alone; they are widely found in the secretory glands of gastrointestinal, respiratory, and genitourinary tracts. The secreted agglutinogens are however not glyco­sphingolipids but glycoproteins (oligosaccharide plus protein). Only about 80% of the population secretes ABO agglutinogens. They are called secretors. The rest are nonsecretors.

Rhesus agglutinogens Unlike the ABO agglutinogens, Rhesus agglutinogens are integral membrane proteins. They are not found anywhere other than on red cells.

ABO agglutinins                    The agglutinins α and β are absent at birth but develop over the first 3 to 6 months of life. They are produced as a result of exposure to ABO-like polysaccharides that are abundant in microbes, seeds, and plants. These natural antibodies are immunoglob­ulins of the IgM type. Subsequent exposures to ABO agglutinogens, as in the course of mismatched transfusion, also produce agglutinins. Such immune aggluti­nins are often of the IgG type.

Rhesus agglutinins       There are no natural antibodies to Rhesus agglutinogens. Agglutinins formed against them are of the IgG type.

Short rewiew:

The Blood

Fluids of the Body

                  Cells of the body utilize 2 fluids:

                 Blood

                                         Composed of plasma and a variety of cells

                                         Transports nutrients and wastes

                 Interstitial fluid

                                         Bathes the cells of the body

                  Nutrients and oxygen diffuse from the blood into the interstitial fluid & then into the cells

                  Wastes move in the reverse direction

 

 

Functions of Blood

                  Transportation

                  O₂, CO₂, metabolic wastes, nutrients, heat & hormones

                  Regulation

                 helps regulate pH through buffers systems (discussed in later chapters)

                                         Carbonic-Acid-Bicarbonate Buffer System

                                         Phosphate buffer system

                                         Protein buffer system

                 helps regulate body temperature

                                         H₂O in plasma has high specific heat capacity, buffering large fluctuations in temp

                                         Vessels direct warm blood to where it’s needed, or to the skin for heat dissipation

                  Protection from disease & loss of blood

 

Physical Characteristics of Blood

                  Thicker (more viscous) than water, and flows more slowly than water

                  Temperature of 100.40 °F

                  pH 7.4   (7.35 – 7.45)

                 If pH 7 is neutral, blood at 7.4 is slightly alkaline

                  Average Blood volume:

                 Females:  4 – 5 Liters

                 Males:  5 – 6 Liters

                 Hormonal negative feedback systems maintain constant blood volume and pressure

 

Components of Blood

                  55% plasma

                   45% cells

                 99% RBCs

                 < 1% WBCs and platelets 

 

Hematocrit (Hct) & Hemoglobin (Hb)

                  Hematocrit (Hct) – percentage of blood volume occupied by RBCs

                 volume of red blood cells ÷ total blood volume

                  Normal Hematocrit range:

                 adult female:  38 – 46% (average of 42%)

                 adult male:  40 – 50% (average of 45%)

                  Hemoglobin (Hb) – the protein responsible for transporting oxygen in the blood

                  Normal Hemoglobin range:

                 adult females:  12 – 16 g/100mL of blood

                 adult males:  13.5 – 18 g/100mL of blood

                  Anemia – not enough RBCs, hemoglobin

                  Polycythemia – too many RBCs (over 50%)

Blood Plasma

                  Over 90% water

                  7% plasma proteins

                                         created in liver

                                         confined to bloodstream

                 albumin

                                         Blood osmotic pressure

                                         Transporter substances

                 globulins

                                         Immunoglobulins (antibodies)

                                         Defense against foreign proteins

                 fibrinogen

                                         Clotting protein precursor

                  2% other substances

                 electrolytes, nutrients, hormones, gases, waste products

 

 

Formed Elements of Blood

                  Red blood cells (erythrocytes)

                  Platelets (thrombocytes)

                  White blood cells (leukocytes)

                 granular leukocytes

                                         Neutrophils

                                         Eosinophils

                                         Basophils

                 agranular leukocytes

                                         lymphocytes (T cells, B cells, and natural killer cells)

                                         monocytes

 

Formed Elements of Blood

                  Normal RBC count:   ~ 5 million/drop

                 Males:   5.4 million/drop

                 Female:  4.8 million/drop

                  Platelet count:  150,000-400,000/drop

                  WBC count:     5,000 – 10,000/drop

Ratio:

RBC   :   Platelet  :   WBC

      700    :      40       :     1

Hematopoiesis: Formation of Blood Cells

                  Most blood cell types need to be continually replaced

                 Blood cells die within hours, days, or weeks

                 Hematopoiesis (or hemopoiesis) – the process of blood cell formation

                  In adults

                 Occurs only in red marrow of flat bones (pelvis, sternum, ribs, vertebrae, & skull, and in ends of long bones)

 

Hematopoiesis of All Blood Cells

All blood cells develop from the same uncommitted stem cells in bone marrow

Red Blood Cells or Erythrocytes

                  Contain oxygen-carrying protein hemoglobin that gives blood its red color

                 1/3 of cell’s weight is hemoglobin

                  Biconcave disk

                 Increased surface area:volume ratio

                 Flexiblity for narrow passages

                 No nucleus or other organelles

                 No mitochondrial ATP formation

                 New RBCs enter circulation at 2-3 million/second

Hemoglobin

                  Hemoglobin Molecule:

>> 4 globular protein subunits

           >> each containing 1 heme group (red pigment)

                   >> each containing 1 iron ion (Fe⁺²)

                            >> each capable of binding (reversibly) to 1 oxygen (O₂) molecule

                  1 RBC  =  ~ 280 million Hemoglobins

                  1 Hemoglobin  =  4 Heme Groups

                  1 Heme Group  =  1 Iron atom  =  1 O₂ molecule

                  Therefore, 1 RBC contains ≈ 1.12 x 10⁹  O₂  molecules

 

 

Function of Hemoglobin

                  Each hemoglobin molecule can carry 4 O₂ or CO₂ molecules

                  Hemoglobin also acts as a buffer and balances pH of blood

                  Hemoglobin transports 23% of total CO₂ waste from tissue cells to lungs for release

                 combines with amino acids in globin portion of Hb

                  Forms of Hb:

                 Oxyhemoglobin:  hemoglobin + O₂

                 Deoxyhemoglobin:  hemoglobin  –  O₂

                 Carbaminohemoglobin:  hemoglobin + CO₂

 

Hemoglobin Affinity

                  CO₂ vs O₂

                 Deoxyhemoglobin’s affinity for carbon dioxide (CO₂) is greater than its affinity for oxygen (O₂)

                 Carbon dioxide (CO₂) can lower O₂-Hb affinity through changes in its partial pressure (pCO₂) or pH (carbonic acid reaction)

                  CO vs O₂  (Carbon Monoxide Poisoning):

                 Hemoglobin’s affinity for carbon monoxide (CO) is 250 times greater than its affinity for oxygen (O₂)

                 CO is colorless, odorless, flammable, and highly toxic

                 CO binds irreversibly to the Fe²⁺ in hemoglobin. Treatment requires oxygen therapy, or hyperbaric oxygen therapy, depending on severity of poisoning

                 The drop in Hb O₂ saturation goes unnoticed for a while because chemoreceptors rely primarily on [CO₂] for the “urge to breathe”

    

Erythropoiesis: Production of RBCs

                  Multipotent stem cell differentiates into Proerythroblast

                  Proerythroblast begins producing hemoglobin, becoming erythroblast

                  Erythroblast ejects nucleus, becoming a reticulocyte

                  Reticulocyte escapes from bone marrow into the blood.

                  In 1-2 days, reticulocyte ejects remaining organelles, becoming Erythrocyte

                  Factors required for Erythropoiesis:

                 Erythropoietin (EPO) from kidneys

                 Vitamin B₁₂ (cobalamin)

                 Iron (Fe)

 

Negative Feedback Control of Erythropoiesis

                  Hypoxia – inadequate oxygen supply to tissues

                 generalized hypoxia – systemic oxygen deprivation

                 tissue hypoxia – local oxygen deprivation

                 Common Causes:

                 High altitudes

                                         decreased atmospheric pressure

                 Anemia

                                         RBC or hemoglobin production < RBC destruction

                  Kidney response to hypoxia:

                 Release Erythropoietin (EPO)

                 Speeds up cell division of erythroblasts, and maturation and release of erythrocytes

 

Negative Feedback Control of Erythropoiesis

Negative Feedback Control of Erythropoiesis

RBC Life Cycle

 

WBC Physiology

                  Less numerous than RBCs

                 5,000 to 10,000 cells per drop of blood

                 1 WBC for every 700 RBC    

                 Only 2% of total WBC population is in circulating blood at any given time

                 Heavily populate lymph, lymph nodes, skin, lungs, & spleen

                 Requires colony stimulating factor (local bone marrow/WBC hormone)

 

Neutrophil Function

                  Fastest response of all WBC to bacteria and parasites

                  Direct actions against bacteria

                 release lysozymes which destroy/digest bacteria

                 release defensin proteins that act like antibiotics

                 release strong oxidants (bleach-like, strong chemicals ) that destroy bacteria

Basophil Function

                  Involved in inflammatory and allergy reactions

                  Leave capillaries (diapedesis) & enter tissues

                  Release heparin, histamine & serotonin

                 heighten the inflammatory response and account for hypersensitivity (allergic) reaction

                 Heparin is a potent anti-coagulant that does not allow clotting within vessels

 

 

Eosinophil Function

                  Leave capillaries to enter tissue fluid

                  Attack  parasitic worms

                  Release histaminase

                 slows down inflammation caused by basophils

                  Phagocytize antibody-antigen complexes

 

 

Monocyte Function

                  Take longer to get to site of infection, but arrive in larger numbers

                  Become wandering macrophages, once they leave the capillaries

                  Destroy microbes and clean up dead tissue following an infection

 

Lymphocyte Functions

                  B cells

                 destroy bacteria and their toxins

                 turn into plasma cells that produce and release antibodies

                  T cells

                 attack viruses, fungi, transplanted organs, cancer cells

                  Natural killer cells (NKC)

                 attack many different microbes & some tumor cells

                 destroy foreign invaders by direct attack

 

 

Differential WBC Count

                  Detection of deviations iormal ranges of circulating WBCs

                 indicates immune response to infection, poisoning, leukemia, chemotherapy, parasites, or allergens

                 Normal WBC counts:

                 Neutrophils:  60-70% (up if bacterial infection)

                 Lymphocyte:  20-25% (up if viral infection)

                 Monocytes:  3 – 8 % (up if fungal/viral infection)

                 Eosinophil:  2 – 4 % (up if parasite or allergy reaction)

                 Basophil:  < 1% (up if allergy reaction)

Blood Types 

                  Agglutinogens – surface antigens on cells

                 Presence or absence of surface antigens determines Blood Type

                 Composed of glycoproteins & glycolipids

                 Antigens:  A, B and Rh (D)

                  Agglutinins – antibodies in the plasma

                  Cross-reactions occur when antigens meet antibodies

 

 

 

ABO Blood Groups

                  Based on 2 glycolipid isoantigens called A and B found on the surface of RBCs

                 display only antigen A — Blood Type A

                 display only antigen B — Blood Type B

                 display both antigens A & B — Blood Type AB

                 display neither antigen — Blood Type O

                  Plasma contains isoantibodies or agglutinins to the A or B antigens not found in your blood

                 Anti-A antibody reacts with antigen A

                 Anti-B antibody reacts with antigen B

 

Blood Type Testing

 

RH blood groups

                  Antigen was discovered in blood of Rhesus monkey

                  People with Rh isoantigens on RBC surface are Rh⁺

                  Normal plasma contains no anti-Rh antibodies

                  Antibodies develop only in Rh^– blood type & only after exposure to the antigen

                  Transfusion reaction upon 2^nd exposure to the antigen results in hemolysis of the Rh⁺ RBCs

 

HDN

                  Rh negative mom and Rh⁺ fetus will have mixing of blood at birth

                  Mom’s body creates Rh antibodies unless she receives a RhoGam shot soon after first delivery, miscarriage or abortion

                  In 2nd child, Hemolytic Disease of the Newborn may develop causing hemolysis of the fetal RBCs

Universal Donors and Recipients

                  People with type AB⁺ blood called “universal recipients” since have no antibodies in plasma

                 AB⁺ blood cells contain all three surface antigens (A, B & D). 

                 Hence, their immune system will not make antibodies to those markers.

                 Only true if cross match the blood for other antigens

                  People with type O^– blood cell called “universal donors” since they have no antigens on their cells

                 O^– RBCs have no surface antigens.  

                 RBCs are “naked” and remain undetected by recipient immune systems.