Consists of various barriers that prevent entry of foreign agents into the body.
If enters they are quickly killed by some other components of this system.
Different types of barriers are as follows:
Physical barriers:
Skin is the main barrier which prevents entry of micro-organism.
Mucous coating of the epithelium lining of respiratory, gastrointestinal and urinogenital tracts helps in trapping microbes.
Physiological barriers:
Acidity of the stomach kills most ingested microbes.
Lysozyme in tears, saliva, and snot kills bacteria by digesting bacterial wall.
Pyrogen released by WBC raise body temperature to prevents growth of microbes in out body.
Interferon induces antiviral state in non-infected cells.
Phagocytic barrier:
Polymorpho-nuclear leukocytes (PMNL-neutrophils), macrophages, and natural killer cells in the blood and tissues kill pathogen by phagocytosis.
Inflammatory barrier:
When there is injury to the tissue there is release of histamine and prostaglandins by the mast cells.
Due to vasodilation there is leakage of vascular fluid containing serum proteins with antibacterial activity.
Further there is influx of Phagocytic cells into the affected area.
Acquired (specific) immunity:
It is also known as adaptive immunity.
This immunity developed after birth when encountered with pathogen.
It supplements the immunity provided by the innate immunity.
Acquired immunity has following unique features:
Specificity: distinguish specific foreign molecules.
Diversity: recognize vast variety of foreign molecules.
Discrimination between self and non-self: it is able to recognize and respond to molecules that are foreign or non-self. It will not respond to our own cell or molecules.
Memory: after responding to the foreign microbes and elimination, this immune system retains the memory of that encounter (primary immuneresponse). The second encounter with the same microbe evokes a heightened immune response. (Secondary immune response)
Acquired immunity is carried out by two special types of lymphocytes:
B-lymphocytes.
T-lymphocytes.
The B-lymphocytes produce a group of proteins in response to pathogen into the blood to fight with them called antibody.
T-lymphocytes do not produce antibody but help B-cells to produce them.
Structure of antibody:
Each antibody has four polypeptide chains.
Two small chains called light chains.
Two longer chains called heavy chains.
Antibody represented as H2L2.
Different classes of antibody produced in out body are IgA, IgM, IgD, IgE and IgG.
AMI vs. CMI:
Immune response by the B-cells by production of antibody is called Antibody mediated immune response or humoral immune response.
Immune response by T-cells is by activation of cytotoxic killer cells which detects and destroys the foreign cells and also cancerous cells called cell mediatedimmune response.
Rejection of organs transplants are due to T-lymphocytes.
Tissue matching, blood group matching are essential for organ transplantation.
Even after tissue typing immune-suppressants is required before and after transplantation.
CBSE Biology (Chapter Wise) Class XII ( By Mr. Hare Krushna Giri )
Email Id : harekrushnagiri@yahoo.com
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