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How does your immune system work? - Emma BryceImmune system defense -
A fully functional immune system can distinguish healthy tissue from unwanted substances. If it detects an unwanted substance, it will mount an immune response — a complex attack to protect the body from invaders like bacteria, viruses, and parasites.
It also recognizes and removes dead and faulty cells. The immune system does not always get it right, however. Sometimes, for instance, it is unable to fight effectively because a person has a health condition or needs certain medications that affect how the system works.
In autoimmune diseases and allergies, the immune system mistakenly perceives healthy tissue as unhealthy and launches an unnecessary attack, leading to uncomfortable and sometimes dangerous symptoms. This article will look at some of the main features of the immune system and how they defend the body from pathogens and other invaders.
It will also look at problems that can arise with the immune system. The immune system consists of a range of components, including:. The lymphatic system forms a network similar to the blood vessels. It carries a substance called lymph instead of blood. Lymph is a fluid that carries immune-related cells to areas that need them.
White blood cells are constantly looking for pathogens. When they find one, they begin to multiply and send signals to other cell types to do the same. What does a high white blood cell count mean? The immune system needs to be able to distinguish healthy from unhealthy cells and tissue to work effectively.
It does this by recognizing signals called DAMPS — danger-associated molecular patterns. In many cases, an antigen is a bacterium, fungus, virus, toxin, or foreign body. But it can also be a cell that is faulty or dead.
The immune system detects pathogen-associated molecular patterns — PAMPs — in the antigen. In this way, various parts of the system recognize the antigen as an invader and launch an attack. What is an antigen test? These cells surround and absorb pathogens and break them down, effectively eating them.
There are several types, including :. Lymphocytes help the body remember previous invaders and recognize them if they return to attack again. Lymphocytes begin their life in bone marrow. Some stay in the marrow and develop into B lymphocytes B cells ; others travel to the thymus and become T lymphocytes T cells.
These two cell types have different roles. B lymphocytes produce antibodies and help alert the T lymphocytes. T lymphocytes destroy compromised cells in the body and help to alert other leukocytes.
Natural killer NK cells are also lymphocytes. NK cells recognize and destroy cells that contain a virus. What do low lymphocyte levels mean?
Once B lymphocytes spot the antigen antibody generators , they begin secreting antibodies. Antibodies are special proteins that lock on to specific antigens. Each B cell makes one specific antibody. For instance, one might make an antibody against the bacteria that cause pneumonia , and another might recognize the common cold virus.
Antibodies are part of a large family of chemicals called immunoglobulins, which play many roles in the immune response:. Antibodies lock on to the antigen but do not kill it — they only mark it for death. The killing is the job of other cells, such as phagocytes. There are distinct types of T lymphocytes, or T cells.
Helper T cells Th cells coordinate the immune response. Some communicate with other cells, and some stimulate B cells to produce more antibodies.
Others attract more T cells or cell-eating phagocytes. Killer T cells cytotoxic T lymphocytes attack other cells. They are particularly useful for fighting viruses. They work by recognizing small parts of the virus on the outside of infected cells and destroying the infected cells.
Also a type of lymphocyte, these contain granules with powerful chemicals. They are useful for attacking many types of unwanted cells. Overall, the immune system becomes stronger on exposure to different pathogens. By adulthood, most people have had exposure to a range of pathogens and developed more immunity.
Once the body produces an antibody, it keeps a copy so that if the same antigen appears again, the body can deal with it more quickly. Some diseases, such as measles, can be severe if they occur, which is why experts recommend vaccination.
If a person has the measles vaccine, they are unlikely to get the disease. If an unvaccinated person has measles once, it is also rare to get it again. In both cases, the body stores a measles antibody.
The antibody is ready to destroy the virus next time it appears. This is called immunity. This innate immunity includes the external barriers of our body — the first line of defense against pathogens — such as the skin and mucous membranes of the throat and gut.
If pathogens manage to bypass the innate immune system, macrophages will attack them. Macrophages will also produce substances called cytokines, which increase the inflammatory response.
Thanks to vaccinations and exposure to various diseases, the body develops a range of antibodies to different pathogens. Doctors sometimes refer to this as immunological memory because the immune system remembers previous enemies.
This is a temporary type of immunity that derives from another person. For instance, a newborn receives antibodies from the mother through the placenta before delivery and in breast milk following delivery.
The most common method is to introduce antigens or weakened pathogens into a person so the individual produces antibodies and does not become sick. Because the body saves copies of the antibodies, it has protection if the threat should reappear later in life.
Some diseases that doctors recommend immunization for include:. Physical and Chemical Barriers Innate Immunity 2. Nonspecific Resistance Innate Immunity 3.
Specific Resistance Acquired Immunity Physical and Chemical Barriers Innate Immunity Physical and chemical barriers form the first line of defense when the body is invaded.
Physical Barriers The skin has thick layer of dead cells in the epidermis which provides a physical barrier.
Periodic shedding of the epidermis removes microbes. The mucous membranes produce mucus that trap microbes. Hair within the nose filters air containing microbes, dust, pollutants Cilia lines the upper respiratory tract traps and propels inhaled debris to throat Urine flushes microbes out of the urethra Defecation and vomiting -expel microorganisms.
Chemical Barriers Lysozyme , an enzyme produced in tears , perspiration, and saliva can break down cell walls and thus acts as an antibiotic kills bacteria Gastric juice in the stomach destroys bacteria and most toxins because the gastric juice is highly acidic pH Saliva dilutes the number of microorganisms and washes the teeth and mouth Acidity on skin inhibit bacterial growth Sebum unsaturated fatty acids provides a protective film on the skin and inhibits growth Hyaluronic acid is a gelatinous substance that slows the spread of noxious agents Nonspecific Resistance Innate Immunity The second line of defense is nonspecific resistance that destroys invaders in a generalized way without targeting specific individuals: Phagocytic cells ingest and destroy all microbes that pass into body tissues.
For example macrophages are cells derived from monocytes a type of white blood cell. Macrophages leave the bloodstream and enter body tissues to patrol for pathogens. When the macrophage encounters a microbe, this is what happens: The microbe attaches to the phagocyte.
The phagocyte's plasma membrane extends and surrounds the microbe and takes the microbe into the cell in a vesicle. The vesicle merges with a lysosome, which contains digestive enzymes.
The digestive enzymes begin to break down the microbe. The phagocyte uses any nutrients it can and leaves the rest as indigestible material and antigenic fragments within the vesicle.
The phagocyte makes protein markers, and they enter the vesicle. The indigestible material is removed by exocytosis. The antigenic fragments bind to the protein marker and are displayed on the plasma membrane surface.
The macrophage then secretes interleukin-1 which activates the T cells to secrete interleukin 2, as described below under specific resistance. Inflammation is a localized tissue response that occurs when your tissues are damaged and in response to other stimuli.
Inflammation brings more white blood cells to the site where the microbes have invaded. The inflammatory response produces swelling, redness, heat, pain Fever inhibits bacterial growth and increases the rate of tissue repair during an infection. Specific Resistance Acquired Immunity The third line of defense is specific resistance.
Here are the steps in an immune response: When an antigen is detected by a macrophage as describe above under phagocytosis , this causes the T-cells to become activated.
The T-cells secrete interleukin 2. Interleukin 2 causes the proliferation of certain cytotoxic T cells and B cells. From here, the immune response follows 2 paths: one path uses cytotoxic T cells and the other uses B cells.
Cytotoxic T Cell Pathway The cytotoxic T cells are capable of recognizing antigens on the surface of infected body cells. The cytotoxic T cells bind to the infected cells and secrete cytotoxins that induce apoptosis cell suicide in the infected cell and perforins that cause perforations in the infected cells.
Both of these mechanisms destroys the pathogen in the infected body cell. Activation of a helper T cell and its roles in immunity: T Cell Pathway T-cells can either directly destroy the microbes or use chemical secretions to destroy them.
At the same time, T cells stimulate B cells to divide, forming plasma cells that are able to produce antibodies and memory B cells. If the same antigen enters the body later, the memory B cells divide to make more plasma cells and memory cells that can protect against future attacks by the same antigen.
When the T cells activate stimulate the B cells to divide into plasma cells, this is called antibody-mediated immunity.
Antibodies Antibodies also called immunoglobulins or Ig's are Y-shaped proteins that circulate through the blood stream and bind to specific antigens, thereby attacking microbes.
The antibodies are transported through the blood and the lymph to the pathogen invasion site. The body contains millions of different B cells, each able to respond to one specific antigen. There are 4 classes of antibodies listed from most common to least common : IgG IgM IgA IgE IgD Each antibody is made of four polypeptide protein chains: 2 heavy chains and 2 light chains.
Antibodies work in different ways: 1. Neutralizing an Antigen The antibody can bind to an antigen, forming an antigen-antibody complex. Activating Complement: Complement is a group of plasma proteins made by the liver that normally are inactive in the body.
Precipitating Antigens Sometimes the antibodies can bind to the same free antigen to cross-link them. Facilitating Phagocytosis The antigen-antibody complex signals phagocytic cells to attack.
The first aystem of defense against non-self Systemm is the Immune system defense, or non-specific, immune response. The innate immune response Syste, of physical, Imnune and cellular defenses against pathogens. The main systemm of the innate immune response is to immediately prevent the spread and movement of foreign pathogens throughout the body. The second line of defense against non-self pathogens is called adaptive immune response. Adaptive immunity is also referred to as acquired immunity or specific immunity and is only found in vertebrates. The adaptive immune response is specific to the pathogen presented. The immune system is the body's defennse against Immune system defense. The immune ih-MYOON system Responsible energy consumption germs and helps Sytem us syystem. Many cells and organs work together to protect the body. White blood cells, also called leukocytes LOO-kuh-sytesplay an important role in the immune system. Some types of white blood cells, called phagocytes FAH-guh-syteschew up invading organisms.
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