The immune system is typically divided into two categories--innate and adaptive--although these distinctions are not mutually exclusive. Innate immunity Innate immunity refers to nonspecific defense mechanisms that come into play immediately or within hours of an antigen's appearance in the body. These mechanisms include physical barriers such as skin, chemicals in the blood, and immune system cells that attack foreign cells in the body.
The innate immune response is activated by chemical properties of the antigen.
Adaptive immunity Adaptive immunity refers to antigen-specific immune response. The adaptive immune response is more complex than the innate. The antigen first must be processed and recognized. Once an antigen has been recognized, the adaptive immune system creates an army of immune cells specifically designed to attack that antigen.
Adaptive immunity also includes a "memory" that makes future responses against a specific antigen more efficient.
Lines of Defense
First Line of Defense
The primary defence against infectious disease are the surface barriers that prevent pathogens from entering the body.
These surface barriers include intact skin (protect external boundaries) and mucous membranes (protect internal boundaries)
Both the skin and mucous membranes release chemical secretions which restrict the growth of microbes on their surfaces. If pathogens cannot enter the host body, they cannot disrupt normal physiological functions and cause disease Physical and Chemical Barriers (Innate Immunity) Physical and chemical barriers form the first line of defense when the body is invaded.
Physical Barriers
The skin has thick layer of dead cells in the epidermis which provides a physical barrier. Periodic shedding of the epidermis removes microbes.
• The mucous membranes produce mucus that trap microbes.
• Hair within the nose filters air containing microbes, dust, pollutants
• Cilia lines the upper respiratory tract traps and propels inhaled debris to throat
• Urine flushes microbes out of the urethra • Defecation and vomiting -expel microorganisms.
Chemical Barriers
• Lysozyme, an enzyme produced in tears, perspiration, and saliva can break down cell walls and thus acts as an antibiotic (kills bacteria)
• Gastric juice in the stomach destroys bacteria and most toxins because the gastric juice is highly acidic (pH 2-3)
• Saliva dilutes the number of microorganisms and washes the teeth and mouth
• Acidity on skin inhibit bacterial growth
• Sebum (unsaturated fatty acids) provides a protective film on the skin and inhibits growth
• Hyaluronic acid is a gelatinous substance that slows the spread of noxious agents.
Second Line of Defense
The second line of defence against infection are the non-specific cellular and molecular responses of the innate immune system. These defences do not differentiate between different types of pathogen and respond the same way upon every infection. Phagocytic leukocytes migrate to infection sites and engulf foreign bodies (dendritic cells then present antigens to lymphocytes). Inflammatory responses increase capillary permeability at infected sites, recruiting leukocytes but leading to localised swelling. Antimicrobial proteins (such as cytokines and complement proteins) regulate immune activity within the body. Fever increases body temperatures to activate heat-shock proteins and suppress microbial growth and propagation
Third Line of Defense
The final line of defence against infection are the lymphocytes that produce antibodies to specific antigenic fragments. Each B cell produces a specific antibody, and the body has millions of different B cells capable of detecting distinct antigens. Helper T cells regulate B cell activation, ensuring that antibodies are only mass-produced at the appropriate times. Both B and T cells will differentiate to form memory cells after activation, conferring long-term immunity to a particular pathogen
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