Discuss the following of mechanism of immune system. First line of defence Second line of defence Third line of defence?

The immune system is a complex network of cells, tissues, and organs that work together to defend the body against harmful pathogens such as bacteria, viruses, and parasites. The immune system has three lines of defense that work together to protect the body from infection.

1. First line of defense: The first line of defense is the body's physical barriers, such as the skin and mucous membranes, which act as a barrier to prevent pathogens from entering the body. These barriers are the body's first line of defense against infection and help to prevent pathogens from entering the body in the first place.

2. Second line of defense: If pathogens do manage to breach the body's physical barriers, the second line of defense comes into play. This includes the innate immune system, which is a non-specific response that helps to fight off pathogens. This line of defense includes cells such as macrophages, neutrophils, and natural killer cells, as well as proteins such as complement and cytokines. These cells and proteins work together to identify and destroy pathogens and help to limit the spread of infection.

3. Third line of defense: The third line of defense is the adaptive immune system, which is a specific response that targets specific pathogens. This line of defense includes T cells and B cells, which are specialized immune cells that can recognize and remember specific pathogens. When the body encounters a pathogen for the first time, the adaptive immune system responds by producing antibodies and memory cells that help to fight off the infection. If the body encounters the same pathogen again in the future, the immune system can mount a faster and more effective response.

Overall, the immune system's three lines of defense work together to protect the body from infection and help to maintain overall health and well-being.

First Line of Defense: Physical and Chemical Barriers

- Skin: Physical barrier that prevents microorganisms from entering the body.
- Mucous membranes: Line the respiratory, digestive, and urinary tracts, producing mucus and antimicrobial substances.
- Stomach acid: Kills ingested microorganisms in the stomach.
- Tears and saliva: Contain antimicrobial substances.
- Coughing and sneezing: Expel microorganisms from the airways.

Second Line of Defense: Innate Immune Response

- Phagocytes: Cells (e.g., macrophages, neutrophils) that engulf and destroy microorganisms.
- Natural killer (NK) cells: Kill virus-infected cells without prior sensitization.
- Complement system: Group of proteins that destroy microorganisms and recruit phagocytes.
- Inflammation: Recruitment of immune cells and fluids to the site of infection.
- Fever: Raises body temperature to inhibit microbial growth.

Third Line of Defense: Adaptive Immune Response

- Antigens: Foreign substances recognized by the immune system.
- Adaptive lymphocytes: Specialized immune cells (T cells and B cells) that recognize specific antigens.
- Antibody response: B cells produce antibodies that bind to and neutralize specific antigens.
- Cell-mediated response: T cells directly kill infected cells or release cytokines that activate other immune cells.
- Memory cells: Long-lived cells that provide rapid and enhanced immune responses upon re-exposure to the same antigen.