Introduction to hematology and blood

                                            INTRODUCTION TO HEMATOLOGY 

Actually, the word Hematology comes from Greek. it means the study of blood. Defined as Hematology is the Branch of science that deals with the study of blood and its components. So, what is blood? Blood is the connective tissue which is liquid in nature. Pinkish red in artery, dark red in vein but by skin covering it looks bluish.

                                                             THE BLOOD 

The blood has two major compartments. The fluid compartment is plasma and the cellular compartment consists of erythrocytes (red blood cells), leucocytes (white blood cells), and thrombocytes (platelets). Blood is the most important diagnostic marker because 90 percent of diseases can be identified by analyzing blood tests. In biochemical measurements like blood sugar level or any infection condition, we can do the C reactive protein level.

Physical properties of blood

        *Color - Red (naked eye)

        *ph- 7.35 to 7.45 (normal condition)

        *Temperature - 38°C 

        *Volume - 8% of the body weight

       *Viscosity -Between 3.5cP to 5.5cP (five times thicker than water)

Major blood collection tubes
#Black ESR tube, to identify the erythrocyte sedimentation rate 
#Yellow-Clot activator jell tube, we can easily separate the plasma   
#GreenLithium heparin tube for Biochemistry    
#Voilet EDTA tube for Hematology
#Red plane tube for Serology and Biochemistry
#Blue sodium citrate tube for coagulation studies
#Transparent plane tube for long-term plasma storage

Erythrocytes

Erythrocytes is a circular biconcave cell without a nucleus. It has a diameter of about 7.5 μm and a thickness of 2μm. It contains hemoglobin the heaviest of all the formed elements of blood. Because of biconcavity, the red blood cell gets a bigger surface area for oxygen diffusion. The erythrocyte can also squeeze itself through a capillary more easily. Hence in diseases where the bio concavity is lost (spherocytosis) many advantages of a normal red blood cell is lost. The erythrocytes are devoid of nucleus and such structures as ribosomes, endoplasmic reticulum, centriole, and mitochondria, there is little ability to metabolize fatty acids and amino acids. It does not have the capacity to synthesize protein. Energy is generated almost exclusively through the breakdown of glucose. The Embden- Meyerhof pathway is responsible for about 90% of the cell's glucose use. The other pathway is functionally deficient or when environmental oxidants exceed their reducing capacity, hemoglobin precipitates (due to globin denaturation) to form "Heinz bodies " along the inner surface of the red blood cell membrane. Its limited metabolism is barely enough to sustain it during its 120-day lifespan in circulation. All these metabolic pathways are closely related and must function in proper coordination if the erythrocyte is to transport oxygen normally and survive in circulation.

         The internal fluid concentration of the erythrocytes is equivalent to about 0.85% sodium chloride. Erythrocytes swell and then rupture in water due to endosmosis and in concentrated sodium chloride they shrink due to exosmosis. The cell membrane of erythrocytes is composed of lipid and protein molecules. The pores in the cell membrane allow potassium ions to pass in and out of the cell. A glycoprotein present on the outer surface of the cell behaves as a blood group antigen. About 95% of the dry weight of a red blood cell is due to the hemoglobin, which picks up and carries discharges oxygen as carbon dioxide.

       The average red cell has a finite life span of about 120 days. In circulation, it is subjected to a variety of metabolic and mechanical stresses. Damage due to the endothelial lining of arterial vessels with fibrin deposition or blood flow turbulence can produce red cell fragmentation and intravascular hemolysis. The erythrocytes at the end of their life span are destroyed in the reticuloendothelial cells. Within the reticuloendothelial cell, the red cell is attached by lysosomal enzyme. The membrane is disrupted, and the hemoglobin molecule is broken down into haem and globin by the action of the enzyme Haem oxygenase. The freed iron is used in the resynthesis of hemoglobin, returned to plasma transferrin, or stored within the reticuloendothelial cell as ferritin and hemosiderin. The protoporphyrin ring is later converted into bilirubin.

The Leucocytes 

The leucocytes or white blood cells (WBC) are nucleated corpuscles. In healthy adults, the number of leucocytes is between 5000 to 10000/cmm of blood. The various types of white blood cells found in circulating blood are given below.

                                        White blood cells or Leucocytes

     Sub-classes and each type in per every hundred leucocytes

      Neutrophils - 50% to 70%

      Eosinophils - 1% to 4%

      Basophils      - 0.2% to 1%

      Lymphocytes - 25% to 45%

      Monocytes    - 2% to 8%

This classification is based on certain morphological characteristics of the leucocytes. when the blood film is stained by using a staining solution containing methyl blue and eosin the nucleus is stained blue by the basic dye. the granules present in some types of leucocytes may be eosinophilic, basophilic, or neutrophilic. Accordingly, the cells are termed eosinophils, basophils, and neutrophils, respectively. The leucocytes containing granules are called granulocytes and those that do not contain granules are called non-granulocytes.

Morphology 

The nucleus of a neutrophil contains several lobes. The number of lobes increases as the cell grows older. In healthy states, the maximum number of lobes in a neutrophil is seven. The eosinophil nucleus is usually bilobed and the nucleus in a basophil is often S-shaped. Neutrophils contain fine cytoplasmic granules while eosinophils and basophils contain very coarse cytoplasmic granules. A small lymphocyte cell contains a nucleus that almost wholly fills up with the cell. The nucleus is not lobed. In large lymphocytes, the amount of cytoplasm is comparatively larger. the monocytes are the biggest of the leucocytes with the nucleus showing indentation. The diameter of agranulocytes ranges between 10μm- 14μm that of lymphocytes between 7 μm- 10μm whereas for monocytes it is 12μm - 20μm.

Functions and properties of leucocytes 

Leucocytes are needed in the body for defense against invading organisms like bacteria, viruses, parasites, and cancer cells. Mainly the neutrophils and monocytes attack and destroy viruses and bacteria in circulating blood. Although the blood monocytes have little ability to fight infectious agents, once they enter the tissue they begin to swell and develop a large number of lysosomes in the cytoplasm. these cells are called macrophages which are capable of combating disease agents. Plasma cells which are derived from lymphocytes, produce immunoglobulins which neutralize the toxin produced by invading organisms.

Functions of neutrophils 

Neutrophils are called upon to act against acute infection. When there is an acute infection, neutrophils promptly come to the spot, cordon area, phagocytize the organism and digest it. The lysosome presents in the neutrophils carry out a large number of proteolytic, amylolytic, and lipolytic enzymes and also other enzyme such as nucleotidases and catalases. These enzymes act upon the phagocytized bacteria and hydrolyze the molecules present in invading organisms. The invading organisms destroy some local tissue which produces some chemicals, notably histamine, serotonin, and bradykinin. The circulating neutrophils adhere to the margins of the blood vessels and come out to act by throwing their pseudopodia into the pores in between the endothelial cells of the lining wall of the capillaries.   

Factors responsible for leukocytosis

leucocyte-inducing factors are released from the infected and inflamed area. When those reach bone marrow via blood causes the release of granulocytes from bone marrow.

Infection may cause stress which in turn causes the release of ATCH. This hormone causes the release of WBC from the marginal pool. More neutrophils appear at the infected and inflated spot. that why the reason for the increase in the WBC count in acute infection

Functions of monocytes 

The circulating monocytes leave the intravascular compartments and form tissue macrophages. these macrophages ingest mainly those bacteria that commonly produce chronic infection. They phagocytize bacteria in acute infections. They also phagocytize tissue debris, organic and inorganic chemicals, and even cancer cells. Giant cells are formed when several macrophages coalesce together. 

Functions of lymphocytes 

Lymphocytes are responsible for the phenomenon called immunity. B -lymphocytes are ultimately converted into plasma cells which produce immunoglobulins. These are present in the gammaglobulin fraction of plasma protein. The immunoglobulin combines with and neutralizes bacteria and various toxic materials invading organisms produce. Cellular immunity is produced by T-lymphocytes. These cells combine directly with the bacteria, viruses, and cancer cells and destroy them.

Functions of eosinophils 

Not much is known about the eosinophils with certainty. Those cells rise in allergic reactions or disorders and also in parasitic infections. The eosinophils can ingest antigen-antibody complex, neutralize histamine, and dissolve clots. A protein called major basic protein present in eosinophils destroys the larval parasites.

Functions of basophils 

The basophils of blood contain histamine, serotonin, and heparin. In the tissues identical mast cells are present. during inflammation, histamine, serotonin, and bradykinin are liberated by the damaged basophils as well as the mast cells. Histamine and serotonin are powerful vasodilators. 

Platelets

Platelets are very small non-nucleated bodies consisting of cytoplasm enclosed within cell membranes. Golgi apparatus and a scanty amount of mitochondria are in the cell. Platelets also contain very fine alpha-granules which probably contain platelets factor 3 and serotonin. Platelets also contain ADP, various clotting factors, and microtubules made up of thrombsthienin, which help the platelets to retract.

The number of circulating platelets is between 100000 to 500000per cmm of blood. when the platelets count goes below the critical count the subject develops haemorrhagic manifestations.

The normal life span of Platelets is between 7 to 14 days. About 10%of the circulating Platelets are utilized daily for the arrest of minor hemorrhages. Of the rest, most of the Platelets are destroyed by the macrophages in the spleen.

Functions 

The main function of platelets or thrombocytes is to assist in haemostasias through various processes as follows.

1.  Platelets aggregate and stick to the exposed collagen of a damage blood vessel. These ways the rent in the blood vessel seals off.

2.  The aggregated platelets release vasoactive substance which lasts for about 30 minutes and helps in the initial process in the arrest of hemorrhage. The platelets also release factor 3 and help in the blood coagulation process.

3.  The platelets can retract and cause clot retraction due to their thrombostenin  contents, which is necessary for forming firm clot.  

4.  Platelets help in coagulation of exudate which follows bacterial infections. These coagulations help to cordon off the bacteria and thus localize the bacterial infection. 

Abnormal CBC report