Immunity System

 Pathogens

Pathogens are biological agent or viruses that cause a disease. Pathogens are for example,

• viruses
• bacteria
• protists
• worms    etc

Against these pathogens, immune system can senses foreign particles + cells and they guard the body through blood and tissues.
Differences between bacteria and viruses are presence of cell. Bacteria has cells so they are alive but viruses are not.

this is virus of influenza

Viruses and their work
Viruses are small infectious agents which replicate only inside the host cells. When they are found outside of host cells, they exist as a protein coat or capsid. Most of them are really small so we cannot see without a microscope. They were found by Friedrich Loeffler and Paul Frosch in 1898. The evidence was that the cause of foot-and-mouth disease in livestock was an infectious particle smaller than any bacteria.

How to work?

1. Viruses' genome which exists in them enters inside the host cell
2. Genome is replicated and transcribed
3. Viral mRNAs are formed and proteins processed
4. Particles assemble inside the host cell, and they go out

Bacteria
Bacteria are large domain single-cell that are prokaryote microorganisms(metabolism and cell wall). They can grow up in  soil, acidic hot spring, radioactive waste, water and deep in the Earth's crust. There are more than one million of kind of bacteria on the earth. However, only one thousand of them were found.

Antibiotics and their works

Antibiotics are substances that defend against metabolic pathways that are found in bacteria, and cure infections. Antibiotics are selective poison. It has been chosen so that it will kill the desire bacteria, but not the cell in our body. There are different type of antibiotic and each of them affects different type of bacteria in different ways. However, antibiotics don't work for viruses since they don't have a metabolism which is affected by antibiotics, they are not blocked by them.


antibiotic destroy only cell wall so it doesn't break human cells



Defense system of the body
First step
The goal is to stop pathogens from entering the body. Our body has some ways that make pathogens to get in the body.

• Skin: Skin have layers that are epidermis and dermis. Epidermis are dead layer superficial and contain keratin that is impermeable as protecting cells. Dermis are thicker than epidermis and contain cells, glands, hairs, capillaries, sensory receptors. Also skin contain acidic environment and keep bacteria from growing. On our skin, there are already some bacteria which we are used to it and have no harm and they prevent other bacterias from working.
• Mucus: Some pathogens enter through air that we breathe. So the respiratory paths have mucous membrane. Cells of mucous membranes create and secrete a lining of sticky mucus. Mucus trap pathogens that are coming into the body, so pathogens cannot reach the cell that would be infected. Mucus locate at trachea, nasal passages, urethra, and vagina.
• Stomach Acid: Some pathogens enter into the body through food and water. So the acidic environment in stomach can kill these pathogens.

Second step
This is for the pathogens that once go inside the body. There are phagocytosis to deal with them.

• Leucocytes: Leucocytes also white blood cells can fight with pathogens that are  already in our body. One type of them is macrophage that works early in the process of fighting with pathogens. They are big white blood cells, and they can change their shape to surround pathogens and take it in through the process of phagocytosis. A macrophage meets a cell and recognizes whether it is a part of the body (self) or not(not-self) based on the protein molecules. If a macrophage meets self cells, they are left alone, and if it meets not-self cells, they are engulfed. Many phagocytes contain lysosome organelles, so they can help digestion chemically.
• Antigen: It is something strange for our body and causes anti-body formation.
• Anti-body: It is protein that recognize and defense antigen.

How to produce antibodies?
After macrophage destroy pathogens by lysosome with enzyme, some pieces of pathogens called antigens remain on the surface of macrophage.

1. Macrophage present antigen to lymphocyte T(T cell).
2. T cells bind to antigens and T calls are activated.
3. T cells present antigens to B cells.
4. B cells are activated and produce anti-bodies. They are specific to each antigens.
5. Anti- bodies stick to antigens and defense their functions.




right virus is with anti-bodies

  Antigens are molecles that are found in cell, and can be found in pathogen. They are anything that are strange for the body.








HIV and Its Issue
HIV(Human Immunodeficiency Virus) is a virus that causes AIDS(acquired immunodeficiency syndrome). AIDS is an illness which is disorder of immunity systemin in the human body. HIV is caused by the transfer of blood, semen, vaginal lubrication, and mother's milk.

Some Issues Related to AIDS
Issues are social discrimination, the expensive of drug treatment, and so on. So some people cannot get job only because they have AIDS, and there are many orphanned children. The cost for treatment of AIDS is expensive such as medicine, so not all patients can take good health cares.