Blood (by Vijay sir )

                                                                         Blood 

Blood :-

        Blood is a specialized connective tissue which is fluid in nature.The total volume of blood in the body is about 6 liters.Blood is slightly alkaline with a pH of about 7.4. The specific gravity of blood  is about 1.055.

Blood composition:
                  Blood is a highly Complex fluid which is composed of two parts a liquid called  the plasma and different types of cells which remain suspended in the plasma. The cells are called the blood corpuscles. The plasma constitutes about 55% and the cell about 45% of the total volume of human blood. The general composition of whole blood is as follows :

 

                      Composition of blood 

Blood cells

1. Erythrocyte or red blood cell:

           The mature human erythrocytes is a circular, biconcave, non-nucleated disc. The average diameter is about 7.6 microns and thickness about 2.2 microns and thickness about 2.2 microns. The edges are rounded and thicker than the center. Hence the central portion appears to have a lighter shade when viewed from the side it looks like a dumb bell. The erythrocyte is made of membranous material which is composed of protein phosphatides and closterol.The inner and outer layer are made up of proteins and middle layer of lipids. The permeability of this membrane is highly selective. The bigger colloidal molecules as well as (potassium sodium etc) are not allowed to pass. But contain crystalloids,urea etc and the cations i.e.Cl,HCO3 etc. are freely permeable.

Composition:

           Each RB C is composed of a colorless involve enclosing semi liquid material 65% water and 35% solids of which 33% is hemoglobin bound to 2% stromal mesh-work of protein phospholipid, cholesterol and neutral fat.Other organic substance are also present.But in very small amount. If the total liquids 60% is phospholipid 30% free cholesterol and 10% fats and cholesterol esters of the salts in the corpuscles,potassium,phosphate is the chief.

Function :

1.First acid base balance :

                          RBC helps to maintain acid base balance.It is carried out by the buffering action of hemoglobin and other intracellular buffers.

2.Respiratory :

              Red cells carry O2 and CO2 .

3. Iron balance :

               By the special permeability of the cell membrane the red cell help to maintain balance of positive and negative ions in the blood.

4. Viscosity of blood :

                                              Red cells help to maintain the viscosity of blood.

5. Pigment formation :

                    Various pigments are derived from hemoglobin after the disintegration of the red cell e.g.bilirubin biliverdin etc.

Span of life

            The average Span of life of a mature red blood corpuscles is about 120 days in man.

       Rouleaux formation is the tendency of RBC to stick to one another like a pile of coin. This occurs due to the discoid shape of RBC'S.
       Polycythemia is a condition where there is an increases in the number of RBC'S.

      Anaemia is a condition where there is a decrease in the number of RBC or haemoglobin.

       Erythropoiesis it is the process by which RBC'S are formed.In the foetus, RBC's  are formed in the liver spleen and red bone marrow. After birth,they are formed only in the red bone marrow of sternum,ribs,vertebral etc. The stage in the development of RBC are as follows:

1. Proerythroblast is the first stage. It is a large cell having a nucleus.It does not have hemoglobin initially. In the latter stage, hemoglobin starts appearing.

2. Normoblast is the second stage. It is a smaller cell with the degenerated nucleus. But hemoglobin is fully present.

3. Reticulocyte develops from normoblast. It contains hemoglobin and reticulum in the cytoplasm.

4. Erythrocytes which is the fully developed RBC. It does not contain reticulum but contain adequate hemoglobin.

              Both vitamin B12 and Folic acid are necessary for the development of RBC.

White blood cell or leucocyte

                            The white blood cell are an important variety of cellS in the blood. These are rich in nucleoprotein and also contain lipid,glycogen,cholesterol ascorbic acid and a variety of proteolytic enzymes.The average total number of white cell is 6000 to 8000 per CU mm.The normal range being 4000 to 11000 per CU mm.The average ratio of the total white cell count with the total red cell count is about 1:700 i.e.for one WBC these are 700 RBC.

Classification of WBC's :  

                         WBC's are classified as:

Granulocytes which are of three types

•       Neutrophils
•       Eosinophils
•       Basophils

Agranulocytes which are of two types

•  Lymphocyte
•  Monocyte

Granulocytes :

            These WBC have granules in two cytoplasm. They have a nucleus which contain two or more lobes. Granulocytes are further  divided into the following three types:

Neutrophils :

           They contain granular cytoplasm which stains with  neutral dyes. The nucleus may contains 2 to 5 lobes. Neutrophils occur to the extent of 65 to 70% of total WBC.

Esnophils :

          These cells are slightly larger than neutrophil. The granular are coarse and closely packed. This granules take up acid stain. The nucleus contains two lobes. Normal is eosnophils count is 2 to 4 percent of total WBC's.

Basophils :

         They contain coarse granules as in a esnophils. But these granules stain blue with basic dyes. The nucleus is kidney shaped or lobulated. The basophils contain heparin,histamine and 5-hydroxytryptamine. Normal basophil count is 0.5 % of total WBC's.

Agranulocytes :

              This type of WBCs do not have granules. But they have a single nucleus which is not lobe. Agranulocytes are further classified into the following two types:

 Lymphocytes :

            They are of two types:

Small lymphocyte :

                 They occur to the extent of 25% of total WBCs. They are smaller in size with a nucleus occupying almost the whole of the cell so there cytoplasm is less.

Large lymphocytes :

                 They are larger in size containing most cytoplasm.

Monocytes :

         They are the largest of WBCs. They occur to the extent of to 2-4% of WBCs contain and eccentric nucleus which is notched in the inner side.

Function of WBC :

1. Protection against infection. This is done by neutrophil and monocyte which engulf bacteria.This process is called the phagocytosis.
2. To acid in the repair of injured tissues.
3. To produce immune substance which defend against diseases. This is done to Lymphocytes through the synthesis of gamma globulin.
4.  Basophil secret and anticoagulant substance called heparin.

Platelet or thrombocytes :

                         These are round or oval shaped cells with biconcave surface. They are roughly one fourth of the size of a RBC. Normal platelet count is 2 - 5 lakh per  CUmm of blood. Platelets do not have a nucleus. But cytoplasm contain distinct granules. They are synthesized by megakaryocytes of bone marrow.

Function of platelets :

1.Thromboplastin liberated from platelet is essential for clotting

2. They close minute lesions in the walls of blood vessels.

3. They aid in body's defence mechanism against bacteria.

4. They contain histamine and serotonin.

5. They contain some antigenic substance also.

    

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