BLOOD

BLOOD

Blood is a red –coloured, viscous fluid connective tissue circulated in the body and is mainly composed of plasma and blood cells.

Physical characteristics of blood

v  Blood is composed of 45% of blood cells and 55% of plasma.

Functions of blood

1.       Blood helps to transport the gases from lungs to the tissues (o₂) and from tissues to the lungs(co₂).

2.       Blood helps to transport the absorbed digested materials to the tissues of the body.

3.       Blood acts as a vehicle through which many substances are transported to their places of activity.

4.       Blood helps to drain out waste materials present in the body.

5.       Blood acts as a great defensive mechanisms.

6.       Blood helps to regulate body temperature.

7.       Blood maintains acid-base balance of the body.

8.       Blood has coagulation property due to which it prevents loss of blood from the body.

9.       Blood helps to transport the hormones throught the body.

 ERYTHROCYTES/ RED BLOOD CELLS (RBC).

v  RBCs are small,circular,disc-shaped cells suspended in the blood plasma.

v  All the cells in groups ,appear as red in colour and thus blood becomes red-coloured.

v  RBCs are produced in the red bone marrow. The process of formation of RBCs in the red bone marrow is called erythropoiesis.

v  Total lifespan of RBCs is 120days.

v  The RBCs contain a substance known as haemoglobin and is enclosed in the stroma of RBCs

v  Haemoglobin is a complex protein of high molecular weight.

v  Haemoglobin consists of a protein material called globin and non-protein material called ‘haem’.

v  The haem contains iron which gives red colour to the haemoglobin.

v  Haemoglobin (Hb)+oxygen(o2)= oxyhaemoglobin(Hbo2).

v  Haemoglobin (hb)+Carbon dioxide (Co2)=Carboxy-haemoglobin(HbCO2).

Normal values of RBCs/Erythrocytes.

1.       In adults -5 million/mm3 of blood.

2.       In male – 5 to 5.5 million/mm3 of blood

3.       In female – 4.5 to 5 million/mm3 of blood.

Functions of RBCs/Erythrocytes.

1.       It transports the gases such as o2 and Co2 in the form of oxyhaemoglobin and carboxyhaemoglobin.

2.       It maintains acid-base balance by buffering action of haemoglobin.

3.       RBCs help to maintain viscosity of blood.

4.       RBCs maintain iron balance of the body.

5.       Various pigments are derived from the haemoglobin after disintegration of RBCs, e.g.bilirubin,biliverdin.

WBCS OR LEUKOCYTES.

The wbcs are colourless cells having,irregular shaped large nucleus.

The normal count of leukocytes is 6000 to 10000/mm3 of blood.

Classification of leukocytes(wbcs)

A.       GRANULOCYTES

They constitute about 75%. These contain granles in the cytoplasm,hence called granulocytes.

1.       Neutrophils : the granules of these cells are stained by neutral dye. The nuclei is many lobed.

Function : they ingest the microbes and destroy it by phagocytosis.

2.       Basophils: the granules of these cells are sustained by basic dye. The nucleus is usually oval or slightly kidney-shaped .

Function : they are responsible for destruction of products of antigen-antibody reactions.

3.       Eosinophils : the granules of these cells are stained by red acidic dye called cosin. The nucleus is many lobed.

Function : phagocytosis.

B.      AGRANULOCYTES

These are mononuclear cells and they do not show presence of granules in their cytoplasm.

1.       Monocytes : these are large cells with large nucleus. The nucleus is convulted kidney –shaped.

  Function : they give phagocytic action.

2.       Lymphocytes : these are produced in the lymph glands hence called lymphocytes.

i.                     Small lymphocytes : the thin rim is present around nucleus and is stained by basic stains.

ii.                    Large lymphocytes: the nucleus is oval, rounded or kidney shaped and is stained by basic stains.

Function : they are responsible for the development of immunity against foreign substances such as microorganisms.

  Functions of leukocytes/WBCs.

v  Wbcs help in the process of phagocytosis.

v  Wbcs help in the formation of fibroblasts to repair the areas of inflammation.

v  Wbcs give secretion of heparin which helps to prevent intravascular clotting(thrombosis).

v  Wbcs prevent allergic reactions by antihistaminic action.

v  Lymphocytes play an important role in the production of antibodies.

Normal values :

1.       Erythrocytes (RBCs):

a.       Average : 5 million/mm3 of blood.

b.      In male : 5 to 5.5 million/mm3 of blood.

c.       In female : 4.5 to 5 million/mm3 of blood.

2.       Leukocytes (WBCs): 6000 to 10000/mm3 of blood.

3.       Thrombocytes (plateletus): 3to 4 lacs/mm3 of blood.

4.       Haemoglobin :

a.       Average : 15gm/100 ml of blood.

b.      In male : 14 to 18 gm/100 ml of blood.

c.       In female : 12 to 16 gm/100 ml of blood.

Bleeding time : it is the time interval between moment at which the blood starts bleeding to the moment at which the blood starts bleeding to the moment at which it exactly stops.

 Or

It is the time required for cessation of bleeding from a small skin puncture.

 Normal value:n1 to 3 minutes( by Dukes method).

Clotting time/ coagulation time : it is the time interval between the moment at which blood escapes from the vessel to the moment at which clot is formed.

Normal value : 3to6 min (by Wrights capillary method).

Blood stream : it is the fluid remaining after formation of clot.

BLOOD COAGULATION :

“When there is an injury to blood vessel, blood comes out and within a few minutes,it losses its fluidity and forms a red-coloured,semisolid jelly-like mass, i.e.clot. this process is known as blood coagulation or blood clotting.”

Mechanism of blood coagulation/ process of blood clotting.

Step I

The injury to blood vessel leads to formation of a rough surface. The platelets when come in contact with rough surface, they are ruptured and thromboplastin is released. It is also released by damaged tissues. This thromboplastin in the presence of calcium converts inactive prothrombin present in the blood into active thrombin.

Prothrombin +thromboplastin +ca++-----> Thrombin .

Step II

The active thrombin converts inactive fibrinogen into insoluble fibrin threads which form a network like structure .

Thrombin +fibrinogen ---------> Fibrin threads .

Step III

In the holes of these network of these fibrin threads the blood cells get entangled to form a red-coloured semisolid jelly-like mass,i.e.clot.

 Thus ,the process of blood coagulation completes.

 Fibrin threads+Blood cells ------> Clot .

Factors affecting /influencing blood coagulation.

a.       Factors Hastening/Accelerating/increasing blood coagulation.

i.

Roman";">                     Contacts of blood with rough surface and injury to blood thrombocytes.

ii.                   Temperature slightly excess than body temperature may increase blood coagulation.

iii.                  Excessive slowness of blood flow.

iv.                 Snake venom.

v.                   Presence of calcium salt.

vi.                 Resting condition.

b.      Factors Hindering /retarding /preventing blood coagulation .

i.                     Contact with smooth surface .

ii.                   Lowering body temperature

iii.                  Removal of Ca++ ions from the blood by addition of Na, K and citrate ions.

iv.                 Presence of greasy material like oil, wax or grease.

v.                   Calcium deficiency in the blood.

vi.                 Use of heparin.

PLASMA PROTEINS :

  The number of proteins present in the blood plasma are called plasma proteins,”. E.g. serum albumin, serum globulin,prithrombin,fibrinogen.

Functions of plasma proteins :

i.                     Plasma proteins maintain colloidal osmotic pressure of the blood and help in regulating the distribution of fluid between the blood and tissues of the body .

ii.                   Prothromobin and fibrinogen are essential for the blood clotting process.

iii.                  Plasma proteins mainly globulins are responsible for maintaining viscosity of blood which ultimately maintains the blood pressure .

iv.                 The plasma proteins act as a buffer which maintain acid-base balance .

v.                   Plasma proteins act as a store house of proteins , from which the tissues can draw proteins during inadequate protein diet.

vi.                 Plasma protein combine with certain substances and help to carry them in bloodstream .

vii.                Plasma proteins helps in binding of drugs and increase the duration of action of drugs .

viii.              Plasma globulins help in the formation of antibodies which give protection against infection .

ABO BLOOD GROUP SYSTEM : 

 

                           ABO blood group system was discovered by Karl Landsteiner in 1900.

i.                     The blood of one person is not always compatible with that of another person , hence before transfusion (donation ) of blood , it must be tasted or compatibility of acceptor’s blood is assured.

ii.                   Only compatibility blood is to be transfused.

iii.                  If incompitable blood is transfused then agglutination of erythrocytes occurs which leads to haemolysis of transfused blood cells (break downof RBCs).therefore, Rh+ve blood is not given to Rh-ve persons.

iv.                 There are four main blood groups.

Blood group A , blood group B, blood group AB, blood group O.

Ø  Blood donor : a person who gives or donates the blood to another person is known as blood donor.

Ø  Blood recipient/blood acceptor: A person who requires or accepts the blood from another person is known as blood acceptor.

Ø  Universal donor : A person who donates the blood to all types of blood groups is known as universal donor.

Ø  Universal acceptor : A person who accepts the blood from all the other blood groups is known as universal acceptor.

Ø  The membrane of erythrocytes contains antigens called agglutinogens and people have natural antibodies in the plasma known as agglutinins.

Ø  The agglutinogens are genetically determined and are of two types i.e.’A’ and ‘B’.

Ø  The agglutinins in the plasma are of opposite type.

Compatibility of blood groups (matching of blood groups)

Importance of blood group

i.                     Blood group study has a great value in blood transfusion.

ii.                   Blood group study helps in the study of various blood disorders.

iii.                  Blood group study is useful in forensic medicines.

iv.                 Blood group study is helpful in experimental purposes.

RH FACTOR :

 It is an agglutinogen(antigen) of “rhesus monkey”.

Apart from antigen ‘A’ and antigen ‘B’ about 80to 90% of the people contain one or more antigens on the membranes of RBCs called Rh-antigen or Rhesus factor.

If Rh factor is present in the persons blood then blood group is described as Rh+ve and if Rh factor is absent in the persons blood then blood group is described as Rh-ve.

Significance /importance of Rh factor.

i.                     Rh factor has a great value in blood transfusion because transfusion of Rh+ve blood to Rh-ve person stimulates the immune response which causes haemolysis of transfused blood cells.

ii.                   Rh factor is helpful in detecting the blood group of child by considering father’s and mother’s blood group study.

THROMBOSIS :

The process of formation of blood clot inside the blood vessel which may block the blood circulation is known as thrombosis.

The clot which is formed inside the blood vessel is known as “thrombus”. Thrombosis may be caused because of slow blood flow or infection to inner side of the blood vessels.

Embolism :

The process of formation of embolus  in the bloodstream which blocks the blood circulation is known as embolism.

The embolus may be bubble of air or in some cases blood clot or debris particle.

Phagocytosis :

The process in which the cell engulfs or ingests the microbes,foreign particles and digests or destroys them within the cell is called phagocytosis, e.g. neutrophils and monocytes actively show phagocytic action.

Haemolysis :

 Haemolysis means breakdown of RBCs.

The haemoglobin comes into the plasma after breakdown of RBCs. This phenomenon is known as laking of blood.

Fibrinolysis :

 The process of breakdown of fibrin threads within the clot by the action of proteolytic enzymes is known as fibrinolysis.

Blood disorders :

1.       ANAEMIA :

Anaemia means decrease in number of RBCs in the blood, or decrease in percentage of haemoglobin in the blood.

Causes :

i.                     Excessive loss of blood.

ii.                   Failure of function of red bone marrow to produce RBCs.

iii.                  Destruction of RBCs by haemolysis.

iv.                 Deficiency of iron in the body

v.                   Defective formation of RBCs.

TYPES OF ANAEMIA :

a.       Pernicious anaemia

b.      Megaloblastic anaemia

c.       Microcytic anaemia

d.      Sickle cell anaemia

e.      Iron deficiency anaemia.

2.       Polycythemia :

“it means an abnormal increase in RBCs in the blood”. In this condition the skin and mucous membranes of the mouth are red and conjunctiva is also red.

3.       Leukaemia :

“ leukaemia means uncontrolled increase in production of WBCs in the blood”. It is also called as cancer of blood.

4.       Leucopenia :

“leucopenia means the condition in which there is a decrease in number of WBCs below 4000/mm3 of blood”.

5.       Leukocytosis :

The condition in which the number of circulating leukocytes increases in the blood circulation.

Pathological leukocytes occurs when a blood leukocyte count is above 11,000/mm3 of blood.

6.       Haemophilia :

a.       It is the condition in which bleeding occurs continuously even with a minor injury or a cut.

b.      In this case blood does not clot

c.       It is a hereditary disease which runs in the families.

7.       Erythroblastosis foetails :

It means the death of the foetus due to mass destruction of its red cells when their Rh-ve blood happens to receive Rhesus antibodies from the blood of mother .