Body fluids

• All living cells have to be provided with nutrients, O2 and other essential substances
• Waste or harmful substances produced have to be removed continuously for healthy functioning of tissues
• Efficient mechanisms for the movement of substances to and from cells are essential
• Different groups of animals have evolved different methods for substance transport
• Simple organisms like sponges and coelenterates circulate water through their body cavities to facilitate substance exchange
• More complex organisms use special fluids within their bodies for substance transport
• Blood is the most commonly used body fluid by higher organisms including humans for substance transport
• Lymph also helps in the transport of certain substances
• This chapter covers the composition and properties of blood and lymph (tissue fluid) and the mechanism of blood circulation
• Plasma


  A straw coloured, viscous fluid constituting nearly 55% of blood, with 90-92% water and 6-8% proteins including fibrinogen, globulins, and albumins
• Fibrinogens are needed for clotting or coagulation of blood
• Globulins are involved in defense mechanisms of the body
• Albumins help in osmotic balance
• Minerals in plasma

  • Na+, Ca++, Mg++, HCO3–, Cl–
• Plasma also contains glucose, amino acids, lipids, etc., as they are always in transit in the body
• Factors for coagulation or clotting of blood are present in the plasma in an inactive form
• Plasma without clotting factors is called serum
• Formed Elements

  Erythrocytes, leucocytes, and platelets collectively called formed elements, constituting nearly 45% of blood
• Erythrocytes (RBC)


  Most abundant cells in blood, lack nucleus, biconcave in shape, contain haemoglobin for transport of respiratory gases, average life span of 120 days
• Leucocytes (WBC)


  Colourless, nucleated, lesser in number, two main categories - granulocytes and agranulocytes
• Types of granulocytes

  • Neutrophils, eosinophils, basophils
• Types of agranulocytes

  • Lymphocytes, monocytes
• Neutrophils and monocytes are phagocytic cells
• Basophils secrete histamine, serotonin, heparin, and are involved in inflammatory reactions
• Eosinophils resist infections and are associated with allergic reactions
• Lymphocytes are of two major types - 'B' and 'T' forms, responsible for immune responses
• Platelets, also called thrombocytes, are cell fragments produced from megakaryocytes
• Lymphocytes (20-25 per cent) are of two major types – ‘B’ and ‘T’ forms. Both B and T lymphocytes are responsible for immune responses of the body
• Platelets, also called thrombocytes, are cell fragments produced from megakaryocytes in the bone marrow
• Blood normally contains 1,500,00-3,500,00 platelets mm–3
• Platelets can release a variety of substances, most of which are involved in the coagulation or clotting of blood
• A reduction in platelet number can lead to clotting disorders, resulting in excessive loss of blood from the body
• Various types of grouping of blood have been done, with two widely used groupings being the ABO and Rh systems
• ABO grouping is based on the presence or absence of two surface antigens (A and B) on the RBCs, with corresponding antibodies in the plasma
• During blood transfusion, the blood of a donor must be carefully matched with that of the recipient to avoid severe problems of clumping (destruction of RBCs)
• Group 'O' blood can be donated to persons with any other blood group, making 'O' group individuals universal donors
• Persons with 'AB' blood group can accept blood from persons with AB as well as other blood groups, making them universal recipients
• Rh grouping is based on the presence or absence of the Rh antigen on the RBCs, with Rh+ve and Rh-ve individuals
• An Rh-ve person, if exposed to Rh+ve blood, will form specific antibodies against the Rh antigens
• Rh group should be matched before transfusions to avoid complications