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Lecture 4: Alterations in hematologic function

Introduction

The cardiovascular system consists of three interrelated components: Blood, the heart, and blood vessels.

Blood is composed of two main components: a liquid portion called Plasma and a cellular portion containing red blood cells (erythrocytes), white blood cells (leukocytes) and platelet (thrombocytes).

Blood contributes to homeostasis by transporting respiratory gasses (Oxygen & CO2), nutrients,ions and hormones to and

from body’s cells. It helps regulate body pH and temperature, and provides protection through its clotting mechanisms and immune defenses

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Components of Blood

Plasma (55%)

91 % Water

9 % Solutes :

Plasma proteins 7% – largest proportion of solutes

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Albumins – 58 % of the proteins – maintain osmotic (oncotic) pressure – hold water in the blood

Globulins – 38 % - antibodies synthesized by plasma cells Clotting factors – fibrinogen – 4 %

2 % mineral salts, sugars, fats, hormones and vitamins.

Blood Cells (45%)

Three types

Erythrocytes/RBCs Leukocytes/WBCs Thrombocytes/Platelets

Plasma vs. Serum

If the liquid part of blood is allowed to coagulate it is called serum - serum is just plasma without the clotting factors

Serum is stable at room temperature and can be stored on a shelf. It is also used for diagnostic testing because it won’t coagulate in the machine and mess

it up (خرابها)!

Physical Characteristics of Blood

Heavier, thicker, and 3-4 X more viscous than water 38o C (100.4oF) pH : 7.35 – 7.45 4-6 liters in an adult Varies with electrolyte concentration and amount of adipose tissue

Blood Volume

Blood volume is about 8% of body weight.

1 kg of blood ≈ 1 L of blood

70 kg X 0.08 = 5.6 Kg = 5.6 L

Plasma (~55% of volume).

Cellular portion ( R.B.C ,W.B.C and Platelets) (~45% of volume)

Hematopoiesis

Hematopoiesis is the process by which blood cells are formed.

All of the cellular components in blood are derived from a common precursor called a stem cell.

In the maturing fetus, early production of erythrocytes (R.B.C’s) takes place in developing blood vessels.

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As gestation continues, the production of both red and white blood cells shifts to the fetal liver and spleen and eventually is localized primarily in the bone marrow.

Hematopoiesis continues in the bone marrow after birth and is a lifelong process.

A number of growth factors and cytokines are involved in regulating the process of hematopoiesis.

A major regulator of red blood cell production is the hormone erythropoietin that is produced by the adult kidney.

Erythropoietin is a glycoprotein released by cells of the kidney in response to the presence of hypoxia.

The erythropoietin that is produced acts directly on stem cells in the bone marrow to promote the proliferation, maturation and release of new erythrocytes.

Red Blood Cells

Red blood cells are bi-concave discs. Mature RBCs don't have a nucleus or any protein making machinery and are destined to

die in about 120 days. In a sense they are not really cells, but remnants of cells with a very specific purpose – to

carry O2 to the tissues of the body. The unique shape of the mature erythrocyte maximizes surface area and facilitates

diffusion of oxygen across the cell membrane. Their shape also allows them to deform and fit in small capillary beds The cell membranes of normal red blood cells must be strong enough to survive transport

under high pressure yet be flexible enough to fit through narrow and winding capillaries. A protein cytoskeleton provides a framework of support to the red blood cell membrane.

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Erythropoiesis

Erythropoiesis is the part of hematopoiesis that deals with the production of RBCs. Erythropoiesis increases when states of hypoxia (O2 deficiency) stimulates the kidneys to release the hormone Erythropoietin (EPO)

EPO circulates to the red marrow and speeds up the maturation and release of immature red cells (Reticulocytes)

The rate of erythropoiesis is measured by the number of immature RBCs (called reticulocytes or “retics”) in the peripheral circulation

A low retic count (<.5%) indicates a low rate of erythropoiesis while an elevated rate (>2%) indicates a high rate of erythropoiesis

Red Blood Cells & Glycolysis

The characteristic RBC shape increases the cell surface area and gives them a high oxygen carrying capacity; because they lack mitochondria, they don’t use any of the oxygen they carry. They rely primarily on glycolysis to meet their metabolic needs.

Glycolysis (from glucose + -lysis degradation) is the metabolic pathway that converts glucose into pyruvate. The free energy released in this process is used to form the high-energy compounds ATP (adenosine triphosphate) and NADH (reduced nicotinamide adenine dinucleotide).

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Hematopoiesis (The role of erythropoietin and hypoxia)

Analysis of Blood Cells

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R.B.C & O2

The function of red blood cells is to transport oxygen to tissues.

This is accomplished by the intracellular protein hemoglobin.

The quaternary hemoglobin protein ( Globin portion) is composed of two α and two β subunits.

Each of the subunits contains a central iron containing protein called a Heme protein (the pigment).

It is the iron atom in the heme protein that binds to molecular oxygen.

Oxygen binds to iron in heme (also CO) 23 % of CO2 is bound to globin portion

As a result of the four iron-containing heme groups, each molecule of hemoglobin can carry four atoms of oxygen.

Hemoglobin Types

In the normal adult, hemoglobin A, which is composed of two alpha and two beta globins (a2b2), is the most prevalent, comprising about 95% of all hemoglobin.

Two minor hemoglobins also occur:

Hemoglobin A2, composed of two alpha and two delta globins (a2d2) comprises 2-3.5% of hemoglobin, while

Hemoglobin F, composed of two alpha and two gamma globins (a2g2), comprises less than 2% of hemoglobin.

Hemoglobin F, or fetal hemoglobin, is produced by the fetus in uterus and until about 48 weeks after birth. Hgb F has a high oxygen-affinity in order to attract oxygen from maternal blood and deliver it to the fetus.

After birth, the production of adult hemoglobin rapidly increases and fetal hemoglobin production drops off.

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RBC breakdown

Healthy RBC’s live about 120 days; the person breaks down about 174 million per minute

RBC’s are removed from circulation by the liver and spleen Broken down into heme and globin portions Globin is broken down into amino acids Iron is removed from heme and stored or recycled Heme is broken down into biliverdin and then into bilirubin Bilirubin is produced when the liver breaks down old red blood cells. Usually eliminated

in bile. Bilirubin is then removed from the body through the stool (feces) and gives stool its

normal brown color. Also it is responsible for the yellow color of bruises. To produce more RBC’s, the body needs sufficient iron and amino acids as well as the

vitamins folate (folic acid) and vitamin B12

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Anemia

Anemia is a condition in which there is a reduced number of red blood cells or decreased concentration of hemoglobin in those cells or both.

Anemia is often a manifestation of some disease process or abnormality within the body.

Although there are many causes of anemia, the actual mechanism by which the anemia results is generally due to :

1- Decreased red cell production, which may be due to lack of nutrient

(B12, folic acid, iron) or bone marrow failure.

2- Increased red cell destruction secondary to hemolysis.

3- Increased red cell loss caused by acute or chronic bleeding.

Anemias may be classified according to cause or effect on red cell morphology

Terms that end with – cytic refer to cell size, and those that end in – chromic refer to hemoglobin content.

Additional terms:

Anisocytosis – various sizes

Poikilocytosis – various shapes

General manifestations of anemia

A major feature of anemia is a reduced capacity for the transport of oxygen to tissues. This reduced oxygen delivery can result in the following:

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Ischemia

Fatigability

Breathlessness upon exertion

Exercise intolerance

Pallor

Increased susceptibility to infection

Classification of Anemia Based on Red Cell Morphology

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Iron Lab Studies

Ferritin : Storage protein of iron Transferrin :

o Plasma protein that transports iron to the bone marrow

o What is measured with serum iron

TIBC : Total Iron Binding Capacity

o What degree of transferrin is open for binding of iron

Iron Studies in Various Disease States

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Morphological classification of anemia

Types of Anemia

We will study:

1) Hemolytic anemia 2) Blood loss anemia 3) Iron-deficiency anemia 4) Cobalamin-deficiency or folate-deficiency anemia 5) Inherited anemia

a. sickle cell anemia and

b. thalassemia

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6) Aplastic anemia 7) Sideroblastic anemia

Hemolytic anemia

Anemia that results from excess destruction of red blood cells (hemolysis) Factors that may cause hemolysis include the following:

o Autoimmune destruction of red blood cells o Certain drugs (example: quinine) or toxins o Cancers such as lymphoma and leukemia o Rheumatoid arthritis o Certain viral infections (parvovirus) o Parasitic infections (malaria)

Blood loss anemia

Anemia that results from acute blood loss. With acute loss of large amounts of blood, shock is the major concern. With chronic loss of smaller amounts of blood, iron deficiency is a chief concern. Causes of acute and chronic blood loss may include the following:

o Trauma and hemorrhage

o Malignancy

o Peptic ulcers

Iron-deficiency anemia

Iron-deficiency anemia is a major cause of anemia worldwide. It can occur as a result of iron-deficient diets.

Vegetarians are at particular risk for iron deficiency as are menstruating or pregnant women due to increased requirement for iron.

Iron-deficiency anemia may also result from poor absorption of iron from the intestine or persistent blood loss (e.g., ulcers, neoplasia).

Because iron is the functional component of hemoglobin, lack of available iron will result in a decreased hemoglobin synthesis and subsequent impairment of red blood cell oxygen-carrying capacity.

Cobalamin-deficiency or folate-deficiency anemia

Cobalamin (vitamin B12) and folic acid are essential nutrients required for DNA synthesis and red cell maturation, respectively.

Deficiency of these nutrients will lead to the formation of red blood cells that are of abnormal shape with shortened life spans due to weakened cell membranes.

One important cause of vitamin B12 deficiency is pernicious anemia that results from a lack of intrinsic factor production by the gastric mucosa.

Intrinsic factor is required for normal absorption of vitamin B12 from the intestine.

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Any intestinal abnormalities (e.g., neoplasia, inflammation) that interfere with the production of intrinsic factor can lead to vitamin B12 deficiency.

Folic acid deficiency most commonly results from poor diet, malnutrition or intestinal malabsorption.

Inherited anemia

Anemia may also result from genetic defects in red blood cell structure or function. Two common genetic disorders of erythrocytes are :

o sickle cell anemia &

o thalassemia

Both of these disorders result from abnormal or absent genes for the production of hemoglobin.

Sickle cell disease

Sickle cell disease is a group of autosomal recessive disorders characterized by abnormal hemoglobin production.

In the United States the highest prevalence of sickle cell disease is in blacks with a reported incidence of approximately 1 in 500 births.

Sickle cell disease has several patterns of inheritance that determine the severity of the disease in afflicted individuals.

In the homozygous form of the disease, most of the hemoglobin formed is defective and the clinical presentation is most severe.

With the heterozygous form of the disease, less than half of the red cell hemoglobin is affected and the presentation is significantly milder.

Individuals may also inherit the sickle cell trait and be carriers of the defective hemoglobin gene without significant clinical manifestations.

Humans contain two copies of each gene, one from the father and one from the mother, which sometimes are referred to as the alleles of a gene.

o If a mutation occurs in just one copy of the gene then that individual is considered heterozygous.

o On the other hand if both copies of a gene are mutated then that individual is homozygous genotype.

Manifestations of sickle cell disease: o The abnormal hemoglobin formed in sickle cell disease results from a substitution

mutation of a single amino acid. o This mutation causes the deoxygenated hemoglobin to clump and become

abnormally rigid. o The rigidity of the defective hemoglobin deforms the pliable red blood cell

membrane and causes erythrocytes to take on “sickled” or half-moon appearance. The degree of sickling that occurs is determined by the amount of abnormal

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hemoglobin within the red blood cell and only occurs when the abnormal hemoglobin is deoxygenated.

o As a result of their elongated shape and rigidity, affected blood cells do not pass easily through narrow blood vessels.

o Hemolysis of sickled red blood cells is also common. The spleen is a major site of red cell hemolysis since the blood vessels found within this organ are narrow and convoluted.

o As a result of the sluggish blood flow, many tissues and organs of the body are eventually affected by this disorder.

Specific manifestations of sickle cell disease may include the following:

o Impaired oxygen-carrying capacity resulting in fatigue, pallor

o Occlusion of blood vessels leading to ischemia, hypoxia, pain

o Organ damage

o Splenomegaly due to increased destruction of red blood cells in this organ.

o Jaundice as a result of increased amounts of hemoglobin released into circulation .

o Increased risk of infection and possible septicemia due to stagnation of blood

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Jaundice

Jaundice occurs when there is an excess of bilirubin in the blood. Normal range of Bilirubin in serum is 0.1–1.0 mg/dL Bilirubin is a breakdown product of heme (Part of Hemoglobin) that is excreted into the

bile. In hemolytic anemia excess rates of red blood cell destruction lead to the production of

bilirubin at rates faster than it can be eliminated from the liver and as a result bilirubin backs up into the blood.

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Bilirubin is pigmented and taints the skin and whites of the eyes with a characteristic yellowish tinge that is indicative of jaundice.

Thalassemia

Thalassemia is a genetic disorder characterized by absent or defective production of hemoglobin α or β chains. As with sickle cell anemia, afflicted individuals may be Heterozygous for the trait and have a milder presentation of the disease or homozygous and have a more severe form of the disorder.

The β form of thalassemia (defective formation of β hemoglobin chains) is most common in individuals from Mediterranean populations, whereas the α form of thalassemia (defective formation of α hemoglobin chains) occurs mostly in Asians.

Both the α and β forms of thalassemia are common in blacks.

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Thalassemia: Pathogenesis

Beta thalassemia(does not produce enough beta globins) results in an excess of alpha globins, which leads to the formation of alpha globin tetramers (α4) that accumulate in the erythroblast (immature red blood cell).

These aggregates are very insoluble and precipitation interferes with erythropoiesis, cell maturation and cell membrane function, leading to ineffective erythropoiesis and anemia.

Alpha thalassemia (does not produce enough alpha globins)results in an excess of beta globins, which leads to the formation of beta globin tetramers β4) called hemoglobin H.

These tetramers are more stable and soluble, but under special circumstances can lead to hemolysis, generally shortening the life span of the red cell.

Conditions of oxidant stress cause Hgb H to precipitate, interfering with membrane function and leading to red cell breakage.

Hemoglobin H-Constant Spring disease is a more severe form of this hemolytic disorder. The most severe thalassemia is alpha thalassemia major, in which a fetus produces no

alpha globins, which is generally incompatible with life.

Oxidative stress is essentially an imbalance between the production of free radicals and the ability of the body to counteract or detoxify their harmful effects through neutralization by antioxidants.

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Clinical classification of β-thalassemia.

1) β-Thalassemia Major

o β-Thalassemia major is associated with:

o •Life-threatening anemia

o •Splenomegaly

o •Bone deformities

o •Other complications

o If left untreated (i.e. no hematopoietic stem cell transplantation [HSCT] or supportive care), 80% of β-thalassemia major patients die within the first 5 years of life due to anemia-related complications.

2) β-Thalassemia Intermedia

o β-Thalassemia Intermedia patients present with symptoms that vary from mild to severe. Most patients have moderate anemia that does not require regular transfusions. Patients present later than those with β-thalassemia major.

3) β-Thalassemia Minor

o β-Thalassemia minor is generally asymptomatic, but carriers sometimes have a mild anemia

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Manifestations of thalassemia

In heterozygous individuals enough normal hemoglobin is usually synthesized to prevent significant anemia. In these individuals symptoms of anemia may appear only with exercise or physiologic stress.

Homozygous individuals are often dependent on frequent transfusions to treat the resulting severe anemia.

Children affected with the homozygous form may suffer severe growth retardation. The widespread hypoxia that can result from impaired oxygen-carrying capacity leads to erythropoietin-induced increases in hematopoiesis that can eventually affect the structure of the long bones.

Severe anemia may also lead to congestive heart failure and marked hepatosplenomegaly.

Excessive hemolysis of red blood cells may occur in severe forms of the disease due to overproduction of the normal hemoglobin subunit. Iron deposits from increased absorption and frequent transfusions may injure the liver and heart as well.

Treatment of sickle cell anemia and thalassemia

Individuals with inherited anemia should avoid physiologic stresses that might exacerbate hypoxia.

Infections should be avoided and promptly treated if they occur to prevent a possible hypoxic crisis.

Proper immunizations and vaccinations should be administered to lessen the chance of infection.

Frequent transfusions of normal erythrocytes are commonly used in individuals with severe forms of inherited anemia during periods of crisis.

These individuals are at risk for iron accumulation as well as contracting blood-borne pathogens such as hepatitis and HIV from improperly screened blood.

Bone marrow transplant may be utilized effectively to cure patients with genetic anemias; however, the procedure carries considerable risk of its own.

Aplastic anemia

Aplastic anemia is a disease in which the Blood Stem Cells in the Bone Marrow are damaged.

This causes a deficiency of all three blood cell types (Pancytopenia):

o Red Blood Cells (Anemia), White blood cells (Leukopenia), and Platelets (Thrombocytopenia).

Aplastic refers to inability of the stem cells to generate the mature blood cells.

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Aplastic anemia may result from a congenital defect in stem cell production or can be caused by exposure to agents that damage the bone marrow such as solvents, radiation, infection, chemotherapeutic drugs and certain antibiotics.

Drug-induced aplastic anemia is usually a dose-dependent phenomenon. The clinical manifestations of aplastic anemia will depend on the extent to which

hematopoiesis is impaired. General symptoms of anemia such as pallor, fatigue and lethargy can occur initially. Bleeding in the skin and from the nose, mouth and body orifices may also occur from a

lack of platelet production by the abnormal bone marrow. Increase susceptibility to infection is also seen as a result of diminished white blood cell production.

The underlying cause of the aplastic anemia needs to be identified and further exposure prevented. Treatment should also include avoidance of physiologic stresses and infection.

Transfusions are effective for temporarily improving oxygen-carrying capacity. In severe cases, bone marrow transplant may offer a cure.

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Sideroblastic Anemia

These are hypochromic microcytic anemia, caused by defects in iron or heme metabolism. There is elevated serum iron.

In sideroblastic anemia, the body has iron available but cannot incorporate it into hemoglobin, which red blood cells need to transport oxygen efficiently.

Characterized by the presence of sideroblasts in the bone marrow.

Sideroblasts are:

Atypical, abnormal nucleated Erythroblasts inside which iron accumulate into the mitochondria of erythroblasts due to the impaired synthesis of heme.

These iron granules that have not been synthesized into hemoglobin, but instead are arranged in a circle around the nucleus forming a ring around the nucleus, and the cells become ring sideroblasts.

Normally, Sideroblasts are present in the bone marrow, and enter the circulation after maturing into a normal erythrocyte.

Congenital causes :

X-linked, Mitochondrial disorders

Acquired causes:

Bone Marrow Disorder :Myelodysplasia (a group of disorders in which immature blood cells in the bone marrow do not mature or become healthy blood cells) that terminates in Acute Leukemia

Chronic Alcohol abuse

Lead Poisoning

Treatment :

Occasionally require transfusion is required

Does not respond to Erythropoietin Therapy

Ring Sideroblast

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Polycythemia

Polycythemia is a disorder in which the number of red blood cells in circulation is greatly increased. There are two categories of polycythemia: relative and primary.

Relative polycythemia results from an increase in the concentration of red blood cells due to a loss of plasma volume.

In contrast, primary Polycythemia ( polycythemia vera) is caused by excessive proliferation of bone marrow stem cells.

Polycythemia vera is a rare neoplastic disorder that occurs in men between the ages of 40 and 60.

A secondary form of polycythemia may occur from excess erythropoietin production as a physiologic response to hypoxia.

Secondary polycythemia may be seen in individuals living at high altitudes, in chronic smokers or in people with chronic obstructive pulmonary disease.

Manifestations

o Increased blood volume and viscosity

o Increased risk of thrombus

o Occlusion of small blood vessels

o Hepatosplenomegaly from pooling of blood

o Impaired blood flow to tissues (ischemia)

o Headache , Dizziness, Weakness ,Increased blood pressure, Itching / sweating

Treatment

o Increasing fluid volume in relative polycythemia

o Periodic removal of blood by phlebotomy (300-500 ml.) to reduce viscosity and volume in primary polycythemia

o Chemotherapy or radiation (Radioactive phosphorus injections) to suppress activity of bone marrow stem cells in polycythemia vera

o Treat underlying condition - Stop smoking

o Prevent thrombosis

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MAHA: Microangiopathic hemolytic anemia; - due to thrombosed vessels or fibrin strands as in DIC, TTP, malignancy

Hallmark: Presence of schistocytes (fragmented red blood cells) in the Peripheral Blood Smear

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