00Why do we have an human defense system?
Everyday, we our bodies are bombarded by thousands of millions of viruses, fungi and bacteria and other organisms. Yet how do we remain so healthy, why don't we catch a cold or get the flu everyday if these things are attacking us, it is because of our human defense system. This elaborate system fends off all attacking potentially dangerous microbes and continues to keep us humans healthy and allows us to work, play and generally live our life.

Our body can be compared to a car, cars function at an optimum level when hey are properly maintaned by its owner or a mechanic. If this is done then the car is able to accelerate faster make better turns and generally perform better. we can be compared to these cars if our human defense system properly keeps all micro-organisms out of our system we are able to function at our best and have a longer happier life. Most or all humans are not aware of our defense system or we simply take it for granted, only when it is really crucial and very important or if it is not functioning properly will we notice its presence.

An analogy of the human defense system compared to a pool

dangerous microbes or pathegons attacking us everyday

00What is exactly our human defense system?00Our human defense system can be classified in three different lines each line is located in a different system of the body. The first line are located in the intugementary system (skin, hair, nails etc.) , the second line of defense is located in the circulatory system (arteries, capilaries etc.) and the third line of defense are cells that are located in the Lypathic and Immune systems (bone marrow spleen etc.). This is a table to further classify the three lines of defense:


three examples for each line of defense
These lines could also be classified as our innate defense system (line 1 and 2) and our adaptive defense system (line 3)

How do we recognize these invaders (pathogens, microbes etc.) from the rest of our body?

Our body before being able to fend off diseases, has to recognize invaders (dangerous microbes) when entering the body. Our human defense system has no eyes to know if these are dangerous invaders or just a normal part of the body, hence it cannot see what to attack. Luckily for us antigens give invades their very own sense as in these antigens carry things that our body can classify as dangerous microbes. There are very many antigens each having there own physical properties, when these antigens reach the receptors of the white blood cells the invaders are recognized, the epitope is the part of the antibody that is recognized by the immune system a.k.a. the human defense system. The white blood cells create antibodies so that it is able to match the shape of the antigen. The white blood cell's antibodies envelope the antigens and when this happen they kill of these dangerous invaders.

White blood cells indentifying a pathogen (an invader)

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First line's function in the human defense system
Line one as clearly shown by its name is our first so called "line" in our defense system. We may not notice or we often take it for granted but our skin and our eternal body parts such as our finger nails, hair and even our ear wax keep and prevent potentially dangerous invaders from entering our bodies.

the most dependable on defense in the first line is the non-permeable, physical barrier itself, the skin.The Skin has three layers, providing a formidable physical barrier to microbes. Sweat, oils, and other skin secretions help neutralize and wash away invaders. And our skin is populated by harmless bacteria that consume nutrients that would otherwise feed enemy invaders. The many cavaties in the body where invaders could enter from such as our digestion, respiratory and urinal tracts also have something to prevent these dangerous invaders or microbes to enter. These cavaties are lined with mucous membranes, these traps the invaders and prevent them from ever entering the body. Every time you blink your eyes, for example, your eyelids wash away microbes much the way windshield wipers sweep away debris. Inhale something that your body knows doesn’t belong, like pollen, and you’ll sneeze the invader out. Saliva and tears both contain the enzyme lysozyme, which destroys bacteria. Any harmful bacteria that somehow manage to sneak down your throat plunge into a deadly acid bath in your stomach. As i mentioned previously this line is an innate defense system which means this line does not focus specify one one type of invader it just stops a whole bunch from entering.

Although this plan seems full proof some dangerous microbes are still able to enter our body if the mucous membrane are weak or if there is a cut in our skin then there the battle really begins. If this occurs then it is up to the second line to prevent them from doing any harm from that point one.

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cross section of the skin, the physical barrier between the body and the outside world

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Parts of the body that contribute to the first line of defense

In my analogy, comparing humans and cars, the first line in the car would be the hood. This is because it is a solid object just stands between the engine of the car and the rest of the car all alone.

Second line's function in the human defense system

As i previously stated, if the mucous line is weal and gets penetrated by the invaders the second line must put a stop to them as quick as possible before they can do any harm. The second line, the inborn defense kicks in and does their part to keep the body healthy.
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The second line are the natural killer cells that were born in our body they swim around in the plasma of our blood in our capilaries, these cells are more widely known as our white blood cells known as phagocytes. These cells gets rid of these foreign invaders by tracking down the dangerous microbes and destroying or gobble them up, quickly. It is as simple as that. These cell realise that they bumped into these invaders knowing that they are pathogens (dangerous microbes) by releasing chemicals that send out signals back to the phagocytes making it know whether to kill, reproduce with or run away from. The way the phagocytes destroy the invader is by the proces of phagocytosis, this is a cellular process where the white blood cells engulf a pathogen and absorb it in the cell's body. This form of defense is also an innate defense system like the first line of defense, this line does not focus on one particular type of invader. Lysosomes within the white blood cell will fuse with the Phagosome and release their powerful enzymes . These enzymes begin to digest the pathogen. Resulting in the absorbtion by the cell, Other debris leaves the cell by Exocytosis.

Yet sometimes in some cases these phagocytes need additional help from other white blood cells from the third and final line of defense to get rid of specific type of invaders.

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a phagocytes at work in plasma of the blood stream

The process of phagocytosis

The second line of defense compared to a car's function would be the self cleaning oil that removes filth from the car and makes it function well yet most of the times it needs help fromt he third line to take care of all the problems.

Third and final line's function in the human defense systemThe third line of defense is very similair to the second. This line also uses white blood cells to destroy invadors yet these blood cells are not born already in the body, they are produced by the body, created, to fight of very specific type of threats.

Here is when the second component of the defense system—the adaptive defense system—is activated. The adaptive defense system consists of white blood cells known as lymphocytes. These cells are armed with highly specific traits that enable them to destroy particular types of enemy invaders. What’s more, lymphocytes never forget a foe or how to destroy it, which is why the adaptive defense system protection is sometimes referred to as acquired which means the dangerous invader will never be able to penetrate our body again. This is because our body recognizes the threat instantly the second time, this will not give it time to be able to cause any damage before it gets destroyed by the third line or the adaptive defense system.

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How cells in the plasma of the blood are classified

When the third and second line work together to destroy pathogens

The third line of defense compared to a car would be a mechanic or a person fixing the car. The person focuses only on one type of problem and when they have fixed the problem the next time it occurs again they will be able to deal with it faster because of past experiences.

The human defense system cannot work without one another it is a team that fights invaders together. The system would not work if only 2 lines are working if that did happen we would die far too easy.
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small visual map of how the defense system works as you can see the defense system need all 4 lines to work properly

What happens if we get infected?

There are many ways for the microbes to get inside our body; one of the many ways is infection. When there’s a cut on our body, the invaders (microbes) will then enter the body since there are billions of harmful invaders (microbes) surrounding us, this will cause cells in our body to be destroyed. The dying cells will then activate an automatic response called inflammation, this will cause dilated blood vessels and increased blood flow. When the inflammation is turned off, it wills eventually draws defensive cells to the cut/damaged area. Another cause of the inflammation is the increase blood flow. The increase of blood flow helps the defensive cells (immune cells) reach where they need to be.