There are four types of pathogens: viruses, bacteria, fungi and parasites. Virus is the only nonliving category, and causes infection by attaching to a cell and inserting DNA into the cell so that when the cell divides, it copies the viral DNA and thus creates more of the virus. Viral replication can occur through the lytic cycle or the lysogenic cycle. The lytic cycle involves the virus destroying the host cell's DNA and taking over the cell's metabolic activities. Once the virus directs the cell's ribosomes to create enough viruses, the cell bursts in a process called lysing, and the new viruses are released. In the lysogenic cycle, the virus inserts its DNA directly into the host cell's own DNA without destroying it. As the cell divides and copies its DNA, it also copies the viral DNA, but it does not destroy the cell and there are no viral symptoms. However, the lysogenic cycle can eventually progress into the lytic cycle.
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| http://health.howstuffworks.com/medicine/modern/light-virus.htm |
Bacteria, a living pathogen, can often be described just by looking at the classification of the bacteria. The word "bacillus" signifies that the bacteria is rod-shaped; "coccus" means spherical, and "spirillus" means spiral. The sexually transmitted disease syphilis is an example of a spirillus bacteria. Furthermore, the prefix "strepto-" means that the bacteria is organized in chains, such as the bacteria that causes strep throat. The prefix "staphylo-" means that the bacteria is organized in clumps.
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| http://steveaoki.dimmak.com/blog/2009/11/useless-information-4-bacteria/ |
Leukocytes are produced in the thymus gland, spleen and bone marrow, collectively called the lymphoid organs. The leukocytes are stored in lymphoid tissue in the form of lymph ducts and bean-shaped lymph nodes, which are part of the lymphatic system. The lymphatic system filters pathogens from the organs in the body using a clear substance known as lymph that circulates around the body. Lymph is able to provide the white blood cells that fight infection and filter out the harmful invaders, dead cells and toxins.
Leukocytes work by first identifying the pathogen. Then, they signal for help and tag the invaders. Next, they destroy the invaders, and lastly, they remember what caused the infection in the first place. There are eight main leukocytes which carry out these functions:
Macrophage - Type of phagocyte that begins the immune system's attack. It devours invaders through phagocytosis, in which it engulfs the invader in a food vacuole, then fuses it with a lysosome to digest it. They also help by cleaning up dead cellular debris.
Antigen - Macrophage displays part of the virus as a flag to help identify other invaders.
Helper T Cells - Type of lymphocyte store in the thymus gland that recruits and activates other immune system cells through chemical messengers. They help B cells produce antibodies to fight illness.
B Cells - Type of lymphocyte stored in bone marrow that tags invaders with antibodies so that they can be easily identified and destroyed. They can become plasma cells that create thousands of antibodies per second.
Antibodies - Proteins created by B cells that tag antigens. They can also neutralize toxins and activate a group of proteins known as a complement, which assists in destroying bacteria, viruses and infected cells.
Killer Cell - Type of lymphocyte that can either devour invaders or release chemicals that destroy them. They work best when they see germs that have been tagged with antibodies.
Cytotoxic T Cell - Type of lymphocyte that destroys cells infected with a virus before the cell copies the viral DNA. It kills the cell by releasing a chemical that infiltrates the plasma membrane and induces cytolysis by making the cell burst.
Memory Cell - Type of lymphocyte that speeds up the immune system if an invader returns.
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| http://www.mayoclinic.com/health/medical/IM00419 |
There are three kinds of immunity:
Innate immunity is the kind of protection humans are naturally born with. Certain invaders that could be lethal to another species have no effect on us. Also, we are born with mucous membranes and special immune cells in the integumentary system which are our first lines of defense when an invader tries to infect.
Adaptive immunity is developed as we are exposed to new pathogens, because memory cells try to prevent us from suffering from that infection again. Immunization vaccines can also help with adaptive immunity by introducing a harmless amount of a pathogen into a person so that they build up enough antibodies to fight if the germ actually infects them in the future.
Passive immunity is a temporary protection. For example, breast milk contains many of the mother's antibodies that can help prepare the baby's undeveloped immune system to fight against pathogens he or she may encounter as an infant.
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| http://wamfitandwell.wordpress.com/2008/06/24 |
Immune disorders fall into four categories:
Immunodeficiency disorders are either present at birth or acquired later in life. A part of the immune system is missing or does not function properly.
Autoimmune disorders are when the body attacks its own tissue as if it were a pathogen.
Allergic disorders are when the body overreacts to a harmless invader called an allergen.
Cancer can occur when leukocytes grow out of control. Lymphoma and leukemia are among the most common childhood cancers.
Two examples of immune disorders:
AIDS (acquired immunodeficiency syndrome) is a disease that slowly destroys the immune system altogether. A virus known as HIV (human immunodeficiency virus) destroys Helper T Cells, which are absolutely essential in protecting us from otherwise harmless infectious agents. AIDS is spread either through birth, unprotected sexual intercourse, or sharing contaminated needles.
Asthma is an example of an allergic disorder in which the lungs become oversensitive to common allergens and triggers the narrowing of the bronchioli, which results in reduced airflow and therefore difficulty breathing.
As I head into the holiday season, I know that I am very thankful for my immune system and everything it does to defend me against foreign invaders. However, it is important to remember that the immune system needs our help too. Studies have shown that proper diet, exercise, and sufficient sleep can all help improve immune function. So, while your leukocytes are working hard to fight crime inside your body, make sure you're taking care of them too.
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| http://wamfitandwell.wordpress.com/2008/06/24 |
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