The immune system is also known as the human defence system; it is made up different cells, tissues, proteins and organs which come together to play different roles in protecting the body from pathogens which are brought about by microorganisms such as: bacteria, parasites and viruses. The main cells which support the immune system include: phagocytes (white blood cells) and lymphocytes.
In this section of the assignment, I will highlight the main functions of the immune system; looking specifically at how the cells of the immune system deal with infections after injuries and how this immunity is maintained in the body’s system.
How the immune system responds to an infection after a cut in the finger:
The human immune system responds to an infection after a cut by the process of inflammation. Inflammation is a non-specific defence response where blood and white blood cells called phagocytes are delivered to the hurt area in order to take immediate action against all kinds of pathogens which have invaded the body.
After microbes and other external substances have entered the open cut, a blood clot will be produced to seal the wound in order to prevent other microbes from entering. After this barrier is placed forward, the process of inflammation can then take place effectively:
Infected cells such as: mast cells and basophils start to produce chemical mediators such as: histamine. When the histamine is released, it helps increase the blood flow by widening the capillaries and arterioles which in turn increase the amount of oxygen and nutrients needed for inflammation to take place effectively.
Increased blood flow also means that there will be more tissue fluid due to the pressure; this formation will not only carry the dead tissue and cells, but will allow them to drain away into the lymphatic vessels.
Likewise, the increased permeability of the capillary walls allows the antibodies, white blood cells and plasma fluid to break through the walls and into the swelling tissues (tissue oedema).
To finalise the healing process, the histamine attracts the white blood cells (phagocytes) sending them to the injured area where they engulf the microbes; some phagocytes, such as the neutrophils will consume them before dying to form a liquid like substance called: pus. In order to clear the area for new growth, the macrophages will also consume and absorb the microbes.
How this immunity is maintained:
Immunity is maintained by the adaptive response system (specific), where specialised white blood cells (lymphocytes) work with the phagocytes in order to identify specific antigens on the surface of microbes before they have a chance of invading the body.
The two types of lymphocytes that play a part in maintaining immunity are: B-cells and T-cells.
Just like B-cells, T-cells are generated in the bone marrow, but the only difference is that they develop in the thymus. Being cell-mediated, these cells will detect antigens both outside the blood and inside the cells before eliminating them. Whether on the outside or inside the cell, the macrophage will present the antigen directly to the T-cells as its surface receptor for stimulation.
Following this stimulation, the T-cell will differentiate into four specialised cells which all work differently to maintain immunity:
Memory T-cells= these act in the same manner as the memory B-cells to ensure that when the same antigen comes around it is dealt with quickly.
Helper T-cells= these work with B-cells to make antibodies and produce a chemical called: cytokines which enables killer T-cells and macrophages to do their job properly.
Killer T-cells= these attach to the antigen and demolish it.
Suppressor T-cells= these turn off the whole process to prevent damaging effects of the immune system.
Likewise, the B-cells are made and grown in the bone marrow and being antibody-mediated (humoral), they will secrete antibodies as surface receptors to help detect antigens in the blood and outside cells.
When the antigens have been detected, the T-helper cells will work with the B-cells to expand into other functional cells known as: plasma cells and memory B-cells. The plasma cells will secrete antibodies which will in turn attach to the antigens making them targets for the macrophages as antigen presenters to take to the T- killer cells in order to be demolished.
For memory and recognition, the B memory cells will ensure that when the same antigen pops up it is dealt with quickly. For example, once someone has recovered from chicken pox, next time this antigen wants to attack the memory B-cells will recognise the antigen and will instruct the body’s defence mechanisms to attack the antigen with the required amounts of T-killer cells; therefore the body would have a fast and effective way of dealing with the chicken pox to maintain immunity.
Task 3 (D2)
In order to protect the body against pathogens, the immune system responds in two different ways: non-specific (innate) and specific (adaptive). This section examines and contrasts the dexterity and adeptness of the role of each defence mechanism.
The innate (normal) defences are known as “immediate” because they act quickly to help prevent any type of microbe from invading the body. Whereas adaptive (adjusted) defences only target specific pathogens and due to their “delayed” response they have to first examine the pathogens before taking action.
Firstly, the non-specific defence mechanism fall into two categories the first and second line of defence. The first line of defence is made up of physical and chemical barriers; the second line comes under cellular defences such as: inflammation and phagocytosis.
The first line of defence also known as external, can be split up into: skin, mucous membranes, secretions and natural substances such as: lysozymes and saliva. The skin and mucous membranes have different characteristics which allow them to keep the microbes away from the surfaces of the body.
The skin consists of a strong outer layer which is made of different cells in particular cells covered in a protein substance called: keratin and tissues such as: connective and epithelial tissues which all come together to prevent any microbe from breaking into the skin. This process is aided by the secreted antibacterial sweat and sebum on the surface of the skin.
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In the same way, mucous membranes which contain ciliated tissues secrete a thick substance called: mucus. The mucus found in areas such as: the nose and throat (respiratory system) helps manoeuvre the microbes and other un-wanted substances away from external and internal areas of the body. Also, the natural chemical barriers such as: tears and saliva consist of an antibacterial enzyme called: lysozome which chemically destroys the bacteria.
If this first line of defence fails to work, the now internal second line of defence will act immediately to prevent further invasion. The process which responds to tissue damage (inflammation) will release chemicals such as: histamine, which is designed to promote (phagocytosis) by attracting macrophages and neutrophils to the surface of inflammation in order to enhance healing by engulfing the microbes.
Although, these lines of defence are ideal for the body, the pain, swelling and heat brought about each time can cause discomfort after the microbes have entered the body.
In contrast to this, adaptive defences hold the third line of defence to help maintain immunity. These are categorised as specific: cell-mediated and humoral (antibody-mediated) defences.
After the non-specific defence has completed its job, the specific immune system takes on the role of finishing it off; the two types of lymphocytes involved in the neutralising and then killing of the invading microbes are: B-cells and T-cells. Both cells mature in the bone marrow, but T-cells normally activate in the thymus gland.
With the help of T-cells (T-helper cells), B-cells will automatically identify the invaders and respond by producing two functioning cells: plasma cells and memory B-cells. The plasma cells will make the antibodies which attach to the antigen, encouraging the T-killer cells to come along and cause destruction. These cells secrete a chemical called: cytotoxic which immediately kills the antigen. As a result, the T-suppressor cells which have differentiated from the T-cells will turn off the whole immune response, clearing away the mess to get ready for the next attack.
After this, due to their ability to remember the B-memory and T-memory cells will be able to prepare for the next antigen that comes to attack.
Despite all the advantages of this defence system, the time it takes to react against the invaders is longer than that of the non-specific defence system which enhances the chances of infection in the body for example: if the body can’t fight that specific virus quick enough it might lead to certain symptoms such as: flu. Also the fact that the pathogens are specific gives a delayed reaction against other pathogens.
In conclusion, each defence system works in its own unique way. However, in my opinion the effectiveness of non-specific defence mechanisms over weighs that of specific defences.
Although the processes involved in non-specific defences cause discomfort to the body, the immediate reaction against invaders is easily stimulated to protect the body against further infection. The fact that this defence system is constantly fighting external attacks from different pathogens shows how strong and effective it is. Whereas specific defences take longer to act and can only react to specific invaders which might lead to a weakened immunity system due to multiple infections in the body.
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