Protection from Pathogens

Despite relatively constant exposure to disease-causing microbes in the environment, humans do not generally suffer from constant infection or disease. Many systems of the body participate in protecting our bodies from pathogens. Here we will explore how the Integumentary, Lymphatic, and Immune Systems ensure the integrity of our bodies.

Before any immune factors are triggered, the integument or skin functions as a continuous, impassable barrier to potentially infectious pathogens. Pathogens are killed or inactivated on the skin by desiccation (drying out) and by the skin’s acidity. In addition, beneficial microorganisms that coexist on the skin compete with invading pathogens, preventing infection.

Under most circumstances, the body is able to defend itself from the threat of infection thanks to a complex immune system designed to repel, kill, and expel disease-causing invaders. Immunity as a whole can be described as two interrelated parts: nonspecific innate immunity and specific adaptive defenses. The nonspecific innate immune response provides a first line of defense that can often prevent infections from gaining a solid foothold in the body. These defenses are described as nonspecific because they do not target any specific pathogen; rather, they defend against a wide range of potential pathogens. They are called innate because they are built-in mechanisms of the human organism. Unlike the specific adaptive defenses, they are not acquired over time and they have no “memory” (they do not improve after repeated exposures to specific pathogens). Specific adaptive immunity is acquired through active infection or vaccination and serves as an important defense against pathogens that evade the defenses of innate immunity. Adaptive immunity is defined by two important characteristics: specificity and memory. Specificity refers to the adaptive immune system’s ability to target specific pathogens, and memory refers to its ability to quickly respond to pathogens to which it has previously been exposed.