The biological barriers are part of the immune system. However, substances and tissues that function as barriers can also be part of other systems, such as the circulatory system or the integumentary system.
- Primary barriers : They are external, nonspecific, innate. They are in contact with the outside. They constitute both physical and chemical protection of the organism.
- Secondary barriers : They are non-specific response body reactions. It is activated when a microorganism or harmful substance crossed the primary barriers.
- Tertiary barriers : They are specific responses, that is, different according to each pathogen ( antigen ). In addition, once the body finds a response to an antigen, the next time its presence is found, it will react immediately with the necessary antibody. In this way vaccines work: they present an antigen to the body in a moderate way, giving it the possibility of developing the antibody for a disease.
Examples of primary barriers
- Skin : In humans and animals, it is the largest organ . It isolates the organism from the surrounding environment but also allows a controlled exchange. When an injury occurs, this protection is interrupted. That is why wounds must be protected. It is a physical barrier.
- Sweat : Creates an acid and salty environment on the skin that is unfavorable for a large number of harmful microorganisms. It is a chemical barrier.
- Tears : They contain lysozyme, an enzyme that prevents the development of pathogenic microorganisms. It is a chemical barrier.
- Mucous : Parts of the skin surrounding organs that connect with the outside. They secrete mucus, preventing microorganisms from entering those organs.
- Bacterial flora : Prevent the presence of microbes in the mucous membranes.
- Saliva : It also contains lysozyme.
Examples of secondary barriers
3D illustration of a Bacteria.
- Phagocytosis : Reaction of white blood cells to infections.
- Monocytes : They are found in the bloodstream and target injured tissues.
- Macrophages : Phagocytous bacteria and harmful cells, as well as cell debris.
- Killer cells : They attack cells that have been invaded by viruses.
- Granulocytes : They react to infections.
Examples of tertiary barriers
- T lymphocytes : Leukocytes that act directly on the pathogen. They cannot detect all antigens.
- B lymphocytes : Leukocytes that create antibodies for each antigen. They develop in the fetus (liver and spleen) and in the adult’s bone marrow.