Body’s Defense Mechanisms: Barriers, Antigens, and Immunity
Body’s Defense Mechanisms
Barriers: Living organisms have developed an intricate network of defenses to prevent the entry of microorganisms. These defenses, or barriers, may be nonspecific, such as the skin, mucous membranes, and specialized cells that perform phagocytosis in macrophages, transported by blood and lymph. Finally, the response may be specific to that microorganism; this response is called immunity. The skin and mucous membranes are the body’s first defensive structures. The skin is a very effective barrier, as microorganisms can only pass through if there is a breakage or injury. The mucous membranes are much more fragile. However, in the natural body openings, mucous cells produce secretions with antimicrobial activity. In eyes, lacrimal glands secrete a substance with tears, lysozyme, which prevents bacterial growth. The movement of the eyelids distributes the liquid across the surface of the eye, providing a very effective washing effect. The nose and airways are lined by ciliated cells, among which are mucus-secreting cells. The mucus traps all solid particles that may have entered with the inspired air. At the same time, the movement of cilia pushes everything outward. The stomach and vagina have a high degree of acidity that hinders or prevents the development of microorganisms or microbes. Sebaceous skin glands secrete a fatty substance with sweat and dead skin cells that fall off the surface of the skin, forming an acid fat layer that protects us from germs. Discarding dead cells also removes the germs that have settled there before they can enter the organism.
Antigens and Antibodies: Antigens are the signs that alert the body and cause antibodies to react. The body can recognize foreign elements (organisms, cells from another living being, etc.) that have entered it. This recognition is possible because the foreign element has certain unique molecules called antigens. There are several types, and each microbe has thousands of copies of each antigen. When one of them is recognized by the body, it reacts by making antibodies against the antigen. Antibodies are molecules that can recognize the antigen and bind to it, ultimately destroying the organism or cell carrying the antigen. Each antibody acts against only one antigen. Antigen and antibody are made “for each other.” Lymphocytes in the immune system carry out actions on several fronts to eliminate the invader. For example, if you are exposed to a particular bacteria, the bacteria enters your body and starts reproducing. All their offspring will have the antigens that correspond to this species. When lymphocytes (a type of white blood cell) come into contact with the antigen, they immediately start making the corresponding antibody. Each lymphocyte produces thousands of antibody molecules. Some antibodies are released into the environment and attack the antigen carrier, such as those made by B lymphocytes. Other antibodies remain in the membrane of the lymphocyte that made them, and this defensive lymphocyte is not only used against pathogenic microbes but also to destroy your own cells that have become cancerous (although these cells are often not detected, hence the severity of the disease), or to cleanse the body of dead cells or cell debris, which is the work of macrophages. They are even used to remove cells from another organism that accidentally entered ours.