Non-Specific Defence Mechanism:
This immunity comprises all those defense elements with which an individual is born and which are always available to protect a living body. It comprises anatomic, physiological, and phagocytic barriers and inflammatory responses.
(1) Anatomical Barriers- These barriers block the entry of organisms into the body. They consist of skin and mucous membranes. Skin provides the first line of defense and acts as a physical barrier against the entry of pathogenic microorganisms. Human skin is a tough outer layer that secretes sweat and sebum. This makes skin acidic and discourages the growth of microorganisms on the skin. Mucous entraps foreign microorganisms and cilia propel microorganisms out of the body.
(2) Physiological Barriers- Factors like body temperature, pH, and various body secretions prevent the growth of many pathogenic microorganisms. Sweat, tears, and saliva contain the enzyme lysozyme that destroys the cell walls of many bacteria and check eye infections and food spoilage respectively. The highly acidic medium in the gastric juice kills pathogenic bacteria in the stomach. Nasal secretion also contains lysozymes which destroy the pathogenic microorganisms. Similarly, interferons (cytokine barriers) are released by the host cells on getting stimulus when the virus attacks them. These interferons are released from the host cell and make the adjoining unattached cells resistant to the virus attack. During this, interferons inhibit viral protein synthesis, viral RNA transcription, and finally its multiplication. Finally, they prevent viruses from taking over cellular machinery.
(3) Phagocytic Barriers- In this, the total count of leucocytes (WBC) increases sharply. Human contains macrophages and neutrophils, (polymorph nuclear leukocytes PMNL) wandering phagocytes, which circulate through the body. Macrophages engulf microbes, viruses, cellular debris, etc. In response to an infection, monocytes are liberated at the site of infection and become converted into macrophages.
(4) Inflammatory Response- It provides a second line of defense with the help of several chemicals. The injured area becomes red, and swollen due to an increased supply of blood. This occurs as a result of the secretion of histamine and prostaglandins from the mast cells that cause local vasodilation. The inflammatory response may be in the region of the wound (local inflammation) or spread all over the body (systemic inflammation).
In local inflammation, the vasodilation of blood capillaries occurs due to the secretion of histamine. It increases the flow of blood as well as the permeability of the capillaries. This causes the escape of plasma into the surrounding tissue. The plasma contains antibodies that combat the spread of infection. In systematic inflammation, the WBCs count increases considerably. This is caused by the toxins released by pathogens or pyrogens compounds released by WBCs in order to regulate the temperature of the body. Moderate fever provides defense by stimulating the phagocytes and inhibiting the growth of micro-organisms.
Besides the phagocytes, natural killer cells kill virus-infected cells and some tumor cells of the body by creating perforin-line pores in the plasma membrane of the target cells. These pores allow entry of water into the target cell, which then sweats and bursts.
The complement system also works in innate immunity. The membrane protein of this system functions in an orderly manner. There is the formation of transmembrane pores in the microbes, which leads to their lysis. Some components of this system coat the invading microbes. This coating enables phagocytes to readily attach to the microbes and destroy them.
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