Essay On Immune System

The Immune System: The Body's Three Lines of Defence

The immune system has the important job of protecting the body from foreign invaders. It is made up of a network of cells (including white blood cells), tissue and organs. The foreign invaders the immune system fight include viruses, bacteria, microbes and pathogens. In order to stop these foreign invaders, there is a process known as immune response that attacks in three different lines of defence. Without this immune response, the body would be constantly under invasion by pathogens trying to attack and induce illness.

These three lines of defence that make up the body's immune response are the physical and chemical barriers, the non specific response and the specific response. These

three responses protect the body at different stages of pathogen invasion and all play different roles in keeping the body safe.

The First Line of Defence:

The first line of defence is physical and chemical barriers, made up of the body's skin and mucous membranes. As the first line of defence, their job is to stop pathogens from getting inside the body by attacking as they enter.

It includes defences such as:
- tears (wash pathogens out of the eyes)
- ear wax (captures pathogens trying to enter the body through the ears)
- urine (slightly acidic, makes the growth of bacteria difficult)
- skin (thick, waterproof, hard to damage, and destroys bacteria in dry
conditions through the chemicals in the secretion of sweat and oils)

All of the parts of the body these things protect (the ears, the mouth, the nose, the eyes and the genitals) are constantly exposed to the environment around the body, and are therefore easy targets for pathogens. However, the thin skin like barriers of mucous at these entry points, along with the chemical barriers, help to defend these places by being able to capture some of the pathogens that try to enter and killing them.

The Second Line of Defence:

The second line of defence is the non specific immune response. It targets and destroys pathogens in the body in a generalised and non specific manor.
This second line of defence is put into work after pathogens have made it through the first line of defence and into the body to take up residence. When this occurs, the body will attempt to remove the pathogens in two different ways - with the first way being considered a 'seek and destroy' approach, that can work on all pathogens. This method is known as the non specific response, and is the first step in the second defence line.

The main parts of this response include:
- blood clotting (stops extra infection caused by skin damage)
- inflammation (increases the amount of blood to an infected area)
- fever (heating the body up is a way of killing some pathogens that
can not survive in extreme heat)

The second response in the second line of defence is the production of white blood cells in the body to help fight and kill the pathogens that have entered.

However, it is only a certain kind of white blood cell that comes out in the non specific response, and it is called a phagocyte - meaning 'cells that eat'. In a process known as phagocytosis, phagocytes can envelope any kind of pathogen within the body and, whilst the pathogen is inside the phagocyte, it can destroy it.

The Third Line of Defence:

The third line of defence in the body's immune response is the specific response. If there are still any pathogens in the body after the first responses have occurred they are targeted according to their type by the third defence. This third defence is a specific immune response, and it produces and binds protein molecules know as an antibodies to specifically target an antigen - which is typically a pathogen itself or a marker molecule on the surface of the pathogen. When the body becomes infected with a pathogen, certain antibodies are created by the third defence to attack that pathogen. Once these antibodies have been produced to fight off specific antigens they are remembered by the body and if the same antigen tries to invade again, it is instantly targeted and destroyed, as the body is now

immune.