Human blood composition,function and importance

 Human blood. in human being and many other animals blood is red fluid which is circulated by blood vessels(arteries,veins,capillaries) and heart.                                           

                                                                                                                                                               Composition of blood. blood is composed of two parts(plasma and cells).                                                                                                                                                                                     1)Plasma. it is the liquid part of blood,which is about 90 percent water and 10 percent  dissolve substances including proteins( albumins,globulins,fibrinogen) .it also contains nutrients like glucose,vitamins and amino acids as well as hormones and waste products( urea,CO2).                                                                                                                                    

Proteins found in plasma and their function.                                                                           1)Albumins.it control osmotic pressure of blood.                                                               2)Globulin.production of antibodies.                                                                                            3)Fibrinogen.it helps in blood clotting.                                                                                                                                        Blood cells(RBC,WBC,Platelets.                                                                                                                         1)RBC(red blood cells).it is also called erythrocytes.it,s shape is biconcave and has red colour because it contain red colour red colour pigment called haemoglobin.                                each cubic millimeter of blood contain 5 millions RBC.   its life span is about 120 days.                                                                                                       2)WBC(white blood cells).they are colourless as they don,t have any pigment.   it,s shape is irregular and is produced by bone marrow.         each cubic millimeter of blood contain 7000 to 8000 WBC.                                                                                                                                                                   Types of WBC.                                                                                1)Neutrophils.phagocytosis of bacteria.                                                                                         2)Lymphocytes.B-cells and T-cells for immunity.                                                                            3)Monocytes.become macrophages.                                                                                      4)Eosinophils.fight parasites and allergies.                                                                                      5)Basophils.release hormone in allergic reaction.                                                                                                                                               Platelets. they are not true cells but are fragment of cytoplasm pinched off from certain bone marrow.each cubic millimeter of blood contain 15000 to 450000 platelets.it,s life span is about 7-12 days.                                                                        

                                                        Functions of blood.blood transport oxygen from lungs to tissues and carbon dioxide from tissues to lungs.it also transport nutrient from digestive system cells and maintain body temperature.                                                             Blood group systems. blood group is determined by a specific antigen found on the surface of RBC.                            an antigen is a substance that stimulates production of human bodies.                                                                                     ABO blood group system.       this group system was discover by karl land in 1900. A human being may have following blood group systems.                                        1)A    2)B      3)AB     4)O                                                                    A person having antigen A on the surface of his blood has blood group A,A person having antigen B has blood group B and a person having both antigen A and B has blood group AB while a person having neither A nor B has  blood group O.                            

Blood transfusion in ABO blood group system.                                                                        transferring of blood from one person to another.              before blood transfusion,it is checked that both the donor and recipient have same blood group.                                if  a person with blood group A receives blood group B,the anti-B antibodies present in recipient,s blood will at once recognize the antigen B present on RBC of donated blood.                                            the anti-B antibodies of recipient will react with the B antigen i the donated RBC and the blood will coagulate.                                                         the coagulated blood blocks the blood flow through blood vessels.                                         the same is true for a person with blood group B transfused with blood A.          Anti-A antibody present in recipient,s blood will coagulate with RBC having antigen-A of donated blood.    A person with blood group AB accepts all type of blood while a person with blood group O can only be given the blood group O,because blood group O has both anti-A as well as anti-B antibodies.