Immune System: Defense Mechanisms and Pathogen Response

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• The immune system can be thought of as a process of protecting the body from invaders, similar to a city's jurisdiction system, where cops and detectives find and eliminate threats to the city's peace.

• The body has various barriers to prevent pathogens from entering, including the skin, epithelial cells, mucosal layers, and normal flora (good bacteria) in the gut.

• The skin is the largest organ of the body and covers the entire body, making it the first line of defense against pathogens.

• Epithelial cells in the gut and intestine also serve as a barrier, and mucosal layers in areas like the eyes provide additional protection.

• The stomach's acidic environment (pH 2 or 3) helps to kill bacteria that enter the body through food.

• Good bacteria in the gut, known as normal flora, help to fight against bad bacteria and produce vitamin K.

• For an infection to progress, these barriers must be destroyed, and the body knows its flaws and is prepared to respond to different types of pathogens.

• The immune system has two lines of defense: innate immunity and adaptive immunity.

• Innate immunity is always present in the body and responds quickly to pathogens, consisting of cells that roam throughout the body and kill foreign substances.

• There are two types of innate defense mechanisms: always-on mechanisms, such as barriers, and immediate response mechanisms, such as complement systems.

• Barriers and complement systems are always present in the body and ready to respond to infection.

• The complement system is a group of chemical factors that target specific pathogens and create pores in bacterial cells, leading to their death.

• Adaptive immunity is a more specific response that takes longer to develop and is activated when the body encounters a pathogen.

• Adaptive immunity involves the production of specific antibodies against pathogens and is also known as delayed response.

• Lymphocytes, including T cells and B cells, are involved in adaptive immunity, with T cells helping other cells and B cells producing antibodies.

• T cells can be divided into CD4 helper T cells and CD8 killer T cells, which help other cells and kill specific targets, respectively.

• The interaction between innate and adaptive immunity is crucial, with innate immunity signaling to adaptive immunity to produce specific antibodies against pathogens.

• The immune system involves both cellular factors (cell-mediated immunity) and chemical factors (humoral immunity), including complement systems and antibodies.

• Cell-mediated immunity involves cells such as antigen-presenting cells, natural killer cells, T lymphocytes, neutrophils, and eosinophils.

• Humoral immunity, also known as antibody-mediated immunity, involves protein factors such as complement systems and antibodies present in the blood plasma.