What Causes Asthma?
To understand asthma, one must first have a basic understanding of how the lungs function. Our lungs are designed to take in oxygen rich air, transfer that oxygen to our blood stream and then remove or exhale the carbon dioxide generated by this process.
A Brief Picture of our Lungs:
 A commonly used visual for the lungs is that of an upside down tree. The trunk of the tree represents the trachea or windpipe which transports the oxygen from the nose or mouth to the lungs. The largest branches of the tree represent the main bronchial tubes and the smaller branches represent the bronchioles. The function of these tubes is to take the oxygen as it enters the lung and spread it evenly throughout both lungs. The leaves represent the alveoli. There are millions of these tiny air sacs or alveoli throughout our lungs and their job is to transfer the oxygen into the bloodstream. The alveoli also help transfer the carbon dioxide back out of the bloodstream in the reverse process.
How Asthma Affects our Lungs:
In a normally functioning respiratory system, air is brought into the bloodstream and carbon dioxide is expelled leaving the perfect balance of oxygen and carbon dioxide throughout. With an asthmatic lung, the bronchial tubes are inflamed and swollen which prevents the respiratory system from allowing adequate flow of oxygen into the system.
The walls of the bronchial tubes are comprised of a variety of cells, muscle tissue and mucus-secreting glands. There are a variety of cells lining the wall of our bronchial tubes. These cells include white blood cells and something called “mast cells”. The mast cells contain potent chemicals which are called “mediators”. It is thought that the release of the chemicals in these mast cells is what causes the inflammation of the bronchial tubes and ultimately the shortness of breath, wheezing and coughing asthmatics experience.
A Brief Description of our Immune System:
Bone marrow, thymus gland, spleen and lymph nodes are the four major components of our immune system. These organs produce proteins, blood cells and a variety of chemicals designed to defend our body against bacteria, parasites, viruses, and allergens. These bacteria, parasites, viruses, and allergens are known as antigens.
B-Cells:
Our immune system is designed to counteract or nullify an antigen when it enters the body. One of the methods that our immune system employs is the production of white blood cells called “B-cells”. The B-cells create a protein to protect our bodies from an antigen. The protein generated by this process is called an “antibody”. This is known in the medical community as “The Humoral Immune System”. So, your body encounters an antigen, develops an antibody and you should become immune to that antigen. Most of our vaccines are based on this theory. They expose us to low levels of antigens and our immune system creates the antibodies to counteract them. Sometimes in this process, our immune system can overreact to an antigen. When our B-cells overreact, we can develop autoimmune diseases such as rheumatoid arthritis. One of the contributing factors to asthma is our body overreacting to non-threatening antigens.
T-Cells:
Another response from our immune system to antigens is called “Cell-mediated immunity”. Our thymus gland produces a cell called “T-cells”. They exist in our lymph nodes and glands. When an antigen reaches our lymph nodes, these T-cells either fight it or suppress it.
These T-cells work in a variety of ways. Some T-cells attack and kill and invading antigen, these are known as killer T-cells. Some T-cells try and suppress an invading antigen, these are known as suppressor T-cells. Then there are helper T-cells. These helper T-cells send out signals (when needed) which bring in other cells to help fight off an antigen. These helper T-cells are broken into two categories: Th1 and Th2. The helper T-cells are very important because they determine the path the immune system takes after being exposed to an antigen.
Asthma, an Allergic Reaction:
 As we discussed, our immune system creates antibodies to combat antigens. The antibodies created by our humoral immune system are broken into five sub-groups and are known as immunoglobulins. These B-cells are abbreviated into IgA, IgD, IgG, IgM, and IgE.
The IgE antibody has a special affinity for the previously mentioned mast cells which line the walls of the bronchial tube. When present, the IgE antibody attaches itself to the surface of the mast cells which stimulates them to release their strong mediators, such as histamine, into the surrounding tissue. These chemicals cause the surrounding tissue to become inflamed and swollen. This becomes a problem with your immune system overreacts to the presence of a common antigen (such as pollen) by overproducing the IgE antibody. The production of too much IgE antibody creates a larger reaction in the bronchial tube which in turn reduces the physical dimension of the bronchial tube and ultimately constricts air flow.
Common antigens found in your environment which the humoral immune system may overact too include animals, dust mites, molds, pollen, and various foods. This overreaction may not happen immediately but rather build up over time and numerous exposures.
Another key component in creating an allergic reaction to outside stimuli are the T-Cells. As we discussed, the helper T-cells are important because they determine how your body’s immune system will deal with an antigen when encountered. The Th1 cells release chemicals know as kytokines the drive the immune system away from an allergic response to an antigen. The Th2 cells, just the opposite. The Th2 cells send out signals that recruit allergy blood cells to the fight. The cells that respond to the Th2 cells signal congregate and again secrete mediators like histamine and leukotrines. These mediators interact with the cell wall causing swelling and inflammation resulting in loss of air flow.
This is where heredity affects your predisposition to asthma. In people who do not have the predisposition for asthma, their DNA programs their body to use the Th1 helper T-cells which do not create allergic reactions. The DNA in people who are predisposed to contract asthma tends to program the body to use the Th2 helper T-cells which do in fact create allergic reactions. Recent studies suggest that one out of five people in the U.S. carry the genetic predisposition for their bodies to use the Th2 helper cell and are thus susceptible to contracting asthma.
Summary:
There is no simple answer to the question of what causes mast cells to release their toxic content. Currently, it is believed that there is a very complex interaction between your genetic background, your immune system and exposure to various environmental triggers. Basically, your genetic make up determines whether or not you are predisposed or susceptible to contract asthma. Then, the interaction between your immune system and your surrounding environment determines whether or not you experience or contract asthma. The things in your surrounding environment that may stimulate the asthma are commonly known as “triggers”.
What exactly causes asthma, we are not 100% sure. What is known is that every asthmatic has chronic airway inflammation and airway sensitivity to certain triggers. Asthma is caused by these triggers, whatever they may be.
Most triggers are from allergic reactions yet some people are born with the tendency to get asthma easier then other people. Scientists are still trying to discover why some people are more prone to asthma then others.
The environment you live in, of course can play a part in your asthma. If you are allergic to something, and you live in an environment which you are in contact with that trigger, this could easily set off your asthma.
Some of the most common triggers that set off asthma are;
- Pollution
- Tobacco Smoke
- Bushfires
- Burning Of Sugar Cane
- Perfumes
- Certain Cleaning Products
- Cold Or Dry Weather
- Exercise
- Cold's, Flu's, Chest Infections, Sinusitis
- Dust - This Is A Big One
Everyone has their own set of triggers that will induce the symptoms of asthma.
Please click on the following links for more detailed articles.
- What Causes Asthma?
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