Medical brain notes 33

  IMMUNOLOGY   Animals and human beings are continually exposed to various infectious agents like bacteria, viruses, fungi and parasites. It has long been noticed that survivors of certain diseases, e.g., measles, are not attacked by the same disease again. Clearly, these people have become immune to the concerned disease. The system of animal body, which protects it from various infectious agents and cancer, is called  Immune system . A study of the immune system is known as  Immunology . This chapter introduces the fundamental concepts of immune system and their use for the improvement of human health and welfare.   The Latin term '  Immunis ', meaning '  exempt ' or '  freedom ', gave rise to the English word immunity. It refers to all the mechanisms used by the body for protection from environmental agents that are foreign to the body. These agents may be microorganisms or their products, certain food items, chemicals, drugs and pollen grains....

  Structure and Functions of the Immune System   The lymphoid system consists of the  lymphoid cells  (lymphocytes and plasma cells) and  lymphoid organs . Based on different roles they perform, lymphoid organs can be classified into  central  ( primary ) and  peripheral  (secondary)  lymphoid organs . The central lymphoid organs are   lymphoepithelial structures in which the precursor lymphocytes proliferate, develop and acquire immunological capability. In mammals, the bone marrow, the thymus and the  bursa of fabricius  in birds represent primary lymphoid organs. After acquiring immunocompetence, the lymphocytes migrate along blood and lymph streams, accumulate in the peripheral lymphoid organs and, following antigenic stimulus, effect the appropriate immune response. The  spleen ,  lymph nodes  and  mucosa - associated   lymphoid tissue  (MALT) constitute the major peripheral or  seco...

  Structure and Functions of the Immune System   The lymphoid system consists of the  lymphoid cells  (lymphocytes and plasma cells) and  lymphoid organs . Based on different roles they perform, lymphoid organs can be classified into  central  ( primary ) and  peripheral  (secondary)  lymphoid organs . The central lymphoid organs are   lymphoepithelial structures in which the precursor lymphocytes proliferate, develop and acquire immunological capability. In mammals, the bone marrow, the thymus and the  bursa of fabricius  in birds represent primary lymphoid organs. After acquiring immunocompetence, the lymphocytes migrate along blood and lymph streams, accumulate in the peripheral lymphoid organs and, following antigenic stimulus, effect the appropriate immune response. The  spleen ,  lymph nodes  and  mucosa - associated   lymphoid tissue  (MALT) constitute the major peripheral or  seco...

  Structure and Functions of the Immune System   The lymphoid system consists of the  lymphoid cells  (lymphocytes and plasma cells) and  lymphoid organs . Based on different roles they perform, lymphoid organs can be classified into  central  ( primary ) and  peripheral  (secondary)  lymphoid organs . The central lymphoid organs are   lymphoepithelial structures in which the precursor lymphocytes proliferate, develop and acquire immunological capability. In mammals, the bone marrow, the thymus and the  bursa of fabricius  in birds represent primary lymphoid organs. After acquiring immunocompetence, the lymphocytes migrate along blood and lymph streams, accumulate in the peripheral lymphoid organs and, following antigenic stimulus, effect the appropriate immune response. The  spleen ,  lymph nodes  and  mucosa - associated   lymphoid tissue  (MALT) constitute the major peripheral or  seco...

  Antibodies - Immunoglobulins   Immunoglobulins (Igs) are  glycoproteins . Each molecule of Ig consists of two pairs of polypeptide chains of different sizes. The smaller chains are called '  light ' (L) chains and the larger ones are called '  heavy '  (H) chains. The L chain has a molecular weight of approximately 25,000 and the H chains is of 50,000. The L chain is attached to the H chain by a  disulphide bond . The two H chains are also joined together by  S-S bonds , depending on the class of immunoglobulins. The H chains are   structurally and antigenically distinct for each class and are designated by the Greek letter corresponding to the immunoglobulin class, as follows :   IgG (Gamma) IgA (alpha ) IgM(mu) Igd (delta) and IgE (epsilon) The L chains are similar in all classes of immunoglobulins. They occur in two varieties,  kappa  (k) and  lambda  ( l ). A molecule of immunoglobulin may have either kappa or l...

  Classification of grafts :  The graft can be classified into four major types.   1.   Autograft  : The tissue of the original donor is grafted back into the same   donor. For example, skin graft from thigh to face in severely deformed case of burnt individuals (plastic surgery).   2.  Isograft  : Graft between syngeneic individuals (ie., identical genetic   constitutuion). For example, clones or identical twins.   3.   Allograft  : (Homograft). Graft between allogenic individuals (ie.,   members of the same species but of different genetic constitution. For example, kidney transplanted from one human to another.   4.  Xenograft  : (Heterograft). Graft between xenogenic individuals (ie.,   different genetic lineage). For example organ transplanted from pig to human, baboon to human.   Genetic basis of organ transplants  :   Success of organ transplants (ie., Cornea, Kidney, Heart, L...