What Is the Nervous System and How Does It Work
There's a variety of subsystems making up your overall immune system, and they all work together to protect your body from illness. The first layers of defense are the physical barriers that separate your inner organs from the outside world. These include your skin, the walls of your gut and the linings of your lungs. Often these barriers are toxic to microorganisms or too difficult for pathogens to penetrate. Various secretions, such as mucus, tears, stomach acid and sweat, also have antimicrobial properties, ridding your body of germs before they have a chance to get inside.
Your body also produces physiological phenomena such as coughing and sneezing, which are primitive reflexes that act to forcefully expel irritants from your body. Diarrhea in response to an ingested pathogen is your body's way of rapidly getting rid of the offending organism.
The Innate Immune System
This system is the first layer of defense that comes into play when a pathogen (such as a bacteria, virus or fungus) penetrates the physical barriers and enters your body. This system acts within hours to recruit immune cells to the site of intrusion via specific chemical messengers. This activates arriving immune cells to remove foreign substances and activate your adaptive immune system.
The cells involved in the innate immune response include phagocytes. These are specialized cells that recognize patterns that are common to pathogens, known as "antigens." Phagocytes engulf the offending intruder, killing it off using a process of digestion. Once the pathogen has been killed off or "neutralized," the phagocyte often displays little bits of the offender on its surface to alert other immune cells.
Neutrophils are another type of white blood cell that contain toxic granules. They're "recruited" to the site of infection, where they bind to and kill off pathogens by releasing their toxic granules. Neutrophils are the most abundant white blood cell, and your body produces over 100 billion of them every day.
A system known as the complement system is a series of chemical reactions that can "tag" pathogens for destruction, recruit more immune cells to the site, directly kill pathogens and remove dead cells. The innate immune system acts rapidly, but it does not form a memory of the pathogen.
The chemicals, called cytokines, released during the immune response are responsible for the characteristic signs of inflammation: heat, redness, swelling and pain. They also raise your body temperature in an attempt to make your body less hospitable to pathogens.
The Adaptive Immune System
Your adaptive immune system produces a stronger and more specialized response. However, it relies on other cells "tagging" or "presenting" foreign or harmful microbes to it in order to function. Thus, it takes this system a little more time to kick in. The main cells in the adaptive immune system are lymphocytes — B cells and T cells — which only recognize an intruder as harmful if it has been properly "presented" to them. When they do recognize a harmful pathogen, they undergo rapid expansion, producing thousands and thousands of the same cell.
T cells are known for rapidly attacking pathogens and releasing cytokines. This process contributes to overall control of the rest of your immune system. B cells notably produce antibodies, which are matched to specific pathogens. Antibodies lock onto those harmful cells when detecting them. This alerts other immune cells to the pathogens and signals that the pathogens are something that should be destroyed.
Once the infection has been cleared, some of the B and T cells persist as memory cells. These keep looking for that same pathogen and will react rapidly to fight it off if they ever encounter it again.
Most of this immune activity is carried out in particular organs, such as your lymph nodes and spleen. Immune cells also travel around your body, carrying out their duties by way of your lymphatic system. This is a network of vessels around your whole body. Immune cells also tend to congregate in glands such as your tonsils, where they work together to eliminate infection. This is the reason you often get swollen glands when you have an infection; these glands are full of immune cells working hard to eliminate the threat.
What Is the Nervous System and How Does It Work
Source: https://www.symptomfind.com/health/what-how-does-immune-system-work?utm_content=params%3Ao%3D740013%26ad%3DdirN%26qo%3DserpIndex