One of the most important systems in the body of any species is the immune system. The immune system is a biological response that protects the body against dangerous pathogens that can cause damage or even death to the body. Without a well-developed immune system adapted to the body of the species, an animal would have no chance of survival. An effective immune system has a myriad of mechanisms to protect the body against pathogens such as viruses and bacteria. The immune system has numerous mechanisms that allow it to protect the body against pathogens, such as mucus, phagocytes and effectors, or even fevers. An animal's skin is one of the first external defenses against infection, as it forms an impenetrable barrier. of the epithelium, which are layers of keratinized cells. Epithelium is a term for the layers of cells that line the outer surface and internal cavities of the body. Although only certain species have skin cells made of keratin, keratin can be found in the feathers of a bird, the scales of a reptile, or in the skin of a human and primate. Because of the many places keratin can be found, this shows us that the outer layer of keratin cells, or what humans have as skin, is not just a front-line defense for humans. The skin is not just an outer layer, but epithelia, layers of keratinized cells, lining the respiratory, gastrointestinal, and urogenital tracts, where infections are common. At the internal surfaces, these internal surfaces are vulnerable to microbial invasion, called mucosal or mucosal surfaces. The mucous surfaces are constantly bathed in the mucus secreted by their glands; These secretions fight the microorganisms that get stuck and grow in the mucus. Mucus is a thick layer of fluid that contains anti...... middle of paper ......f mechanisms that an immune system uses to heal and protect the body. One of them is the mucus produced by glands in the body that captures pathogens entering the openings or most vulnerable places in the body and eliminates them. Another mechanism lies in competent effector molecules that mark pathogens for phagocytes that ingest and then eliminate them. Finally, there is the chemical response of temporarily maintaining a high temperature to kill pathogens that have entered and damaged the body, this is called a fever. The immune system has more than three mechanisms to fight infections and pathogens that enter the body, stopping them before damage is done, healing damage to the body, and eliminating pathogens that cause bodily harm. Works cited1) Parham P 2009. Immune system [Internet]. 3. Quoted in May 2014 1