Defense of The "Living Castle"
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Our immune system behaviors are greatly similar to how a medieval castle works. All the castles have a huge wall surrounding and protecting the inner parts of the castle. This is very alike to our skin which surround our body as a physical barrier to pathogens (Nowicky 945). Pathogen literally means the viruses and other microorganisms that cause diseases. In this case, we can think of them as invaders of the castle (Nowicky 941). No matter how solid and how stable a wall is, there’s always holes to it, and some of the holes on our body are the nostrils, eyes, mouth,etc which make them vulnerable target (Nowicky 945).
Two of our most dangerous enemies are the viruses and bacteria. These two pathogens are greatly different but also somewhat similar. Some differences include bacteria being a single-cell organism and virus is just a piece of DNA that floats around and needs a host to replicate. Both of these are harmful but some of the bacteria are actually helpful to us humans. The one big similar between the two is that both of them doesn’t have a nucleus. To learn more about viruses and bacteria, click this link here.


Picture22.jpgAfter got through the first line of defense, the castle guards will come out to protect the castle. As of the case in our body, the guards are the white blood cells. Three main types of white blood cells are phagocyte, B cells and T cells (Nowicky 946). The phagocytes will kill the pathogens by first engulf then digest them. The T cells can kill the pathogens immediately or signal other cells that are capable of killing it. The B cells kill pathogens by producing antibodies (Nowicky 946). The antibody then have three ways to ways to fight pathogens: inactivate the pathogens, or they can groupthem for phagocytes to do its works or just weaken the pathogen’s membrane (Nowicky 947). Since the functions is to weaken the membrane, and virus don't have any membrane, so antibodies aren't effective on the virus. Our body produces another protein to fight virus, that is interferons. Interferons help stop the virus from replicating. I will explain the whole process of T and B cells killing the pathogens in the next paragraph.









Cellular and Humoral Immunity

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After engulfed by the phagocytes, the antigens are displayed. Antigens are the pathogen’s identities (Nowicky 951). White blood cells use antigens as a way to differentiate between our body cells and the invading cells (Nowicky 951). Helper T cells the come and bond with the antigens (“Human Defense”). The T cells then awake other T cells by sending them a signal. The T cells after awaken will divide into two groups. One turns into killer cells and the other turns into a memory cells(“Human Defense”). The killer cells, as its name suggest will kill the infected cells immediately(“Human Defense”). The memory cells will remember the pathogens so when the pathogens re-invade the body, it can start fighting immediately(“Human Defense”). This whole process of sending out T cells to kill pathogens is called cellular immunity(“Human Defense”). The process of B cells being sent out to kill pathogens is called humoral immunity (Nowicky 953).The only differences between cellular and humoral immunity are that in humoral immunity the cells that engulf the pathogens are not phagocytes, but the B cell itself, and after the T cells are bonded to the antigens, those T cells don’t send signals to wake up other T cells, but it sends out signals to wake up the B cells to start producing antibodies (Nowicky 953). After killing the pathogens, a special type of T cell called suppressor T cells will then inactivate the immune system (“Human Defense”). In conclusion, there are two main jobs for the B cells: be a memory cell and producing antibodies. T cells are responsible for four main tasks: be a memory cell, an activated killer cell, a suppressor cell and a helper T cell (“Human Defense”). To learn more about the humoral and cellular immunity, check out the following two sites by clicking here (This page will explain how humoral immunity is related to other aspects of immunity) and here (This have nice pictures to explain the processes).

Active and Passive Immunity
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Passive immunity is the immunity that was made from another body but was then transferred to our body. Some examples include genetics and your mother’s milk. Both of them weren’t created in our body but was passed to us from our mothers (“Human Defense”). If there is a name for the immunity that weren’t created in our body, there’s also a name for the immunity that we acquire after interact with the pathogens, that is active immunity. Active immunity can either be natural or artificial. In a natural active immunity, our body produces the memory cells. Recall from the previous paragraph memory cells are cells that remember then pathogens so when that same pathogens attack again, the can start the fight immediately (“Human Defense”). In a artificial active immunity, we are injected with vaccines which contains the a specific weakened pathogens so our body can make memory cells for it (“Human Defense”).To learn more active and passive immunity, click here.





Fever and Inflammation
Once we get a fever or an inflammation, we most of the times don’t like it because we feel weird and out of ordinary but these two events are actually a signal that your immunity is working. Fever is a sudden increase in temperature of your body. A slight fever helps speed up the process of maturation of white cells so these cells can fight the invading pathogens. While low fever is helpful, high fever can cause great damages to your body and can even kill you. Fever is also an example of a break up of the homeostasis caused by pathogens (Nowicky 951). In the case of inflammation, from an outside view, inflammation looks like a big swellings accompany with pain, redness,etc but from a zoom-in view, the blood vessels are spreading out to make ways for the white blood cells to the infected area (Nowicky 950).
Human Immunodeficiency Virus (HIV)
Out of all the diseases that have been haunting us for decades, HIV is the one of the most dangerous one. The reason HIV so dangerous is that, as its name suggests, this virus attacks our immune system. This virus attacks our body through direct contact between our blood or mucous membrane with the infector’s blood and other fluids. Once the virus gets into our bloodstream, it will attach to the T cells. The virus will change the “programming” of the cell to make it replicate it selves and also replicate the viruses. Once the T cells are infected, it aren’t working anymore and other minor bacteria and viruses will attack the body (Nowicky 961).
Tissue Rejection
Antigens, recall from the first section, are the pathogens identity. White blood cells use antigens to not mistake pathogens with body’s cells. This is very useful but in some cases, it’s not. When you get a transplanted organ, because this is unfamiliar to the white blood cells, our immunity will fight it immediately. This situation is called tissue rejection. Doctors will often give us drugs to weaken our immune system so they can get the transplanted organs into the patient’s bodies (Nowicky 954).

Biology Vocabs
Pathogen: viruses and other microorganisms that cause diseases

Immune system: A system that protects against pathogens and infections

Phagocytes: One of the three main types of white blood cells, kill the pathogens by engulfing and digesting it

B cells: One of the three main types of white blood cells, kill pathogens by producing

T cells: One of the three main types of white blood cells, either kill pathogens directly or signal other cells to kill it.

Antibodies: Proteins that have three functions: inactive the pathogens, group the pathogens or weaken its membrane

Interferons: Proteins that stop viruses from replicating

Passive immunity: Immunity created from another organism but then pass on to our body

Active immunity: Immunity our body acquire after interacting with pathogens

Inflammation: Red swelling with pain, itches-making ways for white blood cells to the infected areas

Antigens: Pathogens identity

Memory cells: After defeating specific pathogens, these cells are made for later fight

Cellular immunity: Use T cells to kill pathogens

Humoral immunity: Use B cells to kill pathogens

Tissues rejection: White blood cells rejected transplanted organs.

Works Cited
"Bacteria vs. Virus." Diffen. Web. 15 May 2011.
<http://www.diffen.com/difference/Bacteria_vs_Virus>.
General Defence System. Digital image. Web. 14 May 2011.
<http://leavingbio.net/The%20Human%20Defence%20System-web-2.htm>.
"The Human Defence System." Web. 14 May 2011.
<http://leavingbio.net/The%20Human%20Defence%20System-web-2.htm>.
Nowicki, Stephen. "Immune System and Disease." McDougal Littell Biology.Evanston,
IL:McDougal Littell, 2008. 938-69. Print.
Types of Immunity. Digital image. HUMAN BIOLOGICAL SCIENCE UNIT 3B. WestOne
Services. Web. 14 May 2011.
<http://tle.westone.wa.gov.au/content/items/969144ed-0d3b-fa04-2e88
8b23de2a630c/1/human_bio_science_3b.zip/content/004_internal_defence/page
10.htm>.Types of Vaccines. Digital image. Web. 14 May 2011.