The Physiology Of Asthma

Medical research in the past decades has seen an explosion in our understanding of the allergic processes including asthma. These processes occur basically as a result of hyper responsiveness that is inherent in certain individuals.

This disease process manifests itself as a variety of symptoms, some of which include wheezing, cough, and chest tightness, shortness of breath and sputum production.

This can be understood by the fact that whenever the body recognizes an antigen that is a foreign body; it tries to remove it or minimize its effect on body’s own cells by a mechanism known as inflammation. It is actually this immune response that is exaggerated in certain individuals that leads to allergic asthma. There are two types of responses which human body can produce, a primary response and a secondary response.

A primary response occurs on first exposure to an antigen or a foreign body. It is short lived starting after sometime and producing less mediators or chemical substances but capable of causing sensitization. Whenever the body is exposed again to the same antigen, a secondary response occurs. It occurs readily, is more severe and produces more inflammatory mediators, hence leading to more signs and symptoms.

These responses produce changes in the body which constitute the signs and symptoms of the disease. Inflammation anywhere in the body manifests as few cardinal signs. These include redness, heat production, pain at the site of inflammation, swelling at the site and inability of the tissues to perform their function. When these changes occur in the lungs they give rise to the symptoms of asthma. In order to explain physiology of asthma, one should be aware that lungs are two large, soft organs of sponge-like consistency located within the chest.

Heart is located in the center of the chest. Lungs are separated from the abdomen by a strong dome-shaped muscle, the diaphragm. The diaphragm moves down when one inhales and exhales air. During normal breathing, the lungs also change shape, expanding during inspiration and contracting during expiration.

The main function of the lungs is to supply adequate oxygen to the blood and to remove carbon dioxide from the blood. The proper exchange of these gases between outside air and the air in the depths of the lungs depends on clear air passages. Air enters the body through the nose and mouth and travels down into the smaller airways which are called bronchi and bronchioles.

The smallest airways are microscopic in size and end in clusters of tiny air sacs called alveoli. There are some 300 million of these small balloon-like air sacs in the adult lung. Each is surrounded by a network of very fine blood vessels called capillaries. The walls of these capillaries and those of the air sacs are thin which permits the passage of gases between the airway system and the blood. During inhalation that is breathing in the lungs fill with air containing oxygen which can then enrich the blood.

During exhalation breathing out, carbon dioxide which has been removed from the blood is expelled by the lungs. When there is excessive mucous or secretions as a result of inflammation of the airways, it causes swelling and tightening of the smooth muscle around the airways, with the result that air flow is restricted and the normal functions of the lung are affected and finally breathing becomes more difficult.

It is not known whether all cases of asthma require a specific stimulus or not.

The immunologic pathways, various mediators, and inflammatory cells that participate in allergic diseases have all been subject to intense scrutiny. In parallel, a wide range of drugs has become available to the practitioner who manages allergic diseases, and for the first time many agents are based on an understanding of specific inflammatory pathways in allergic disease.

But, despite this increased understanding and the new pharmacological agents, the worldwide epidemic of allergic disorders continues. This epidemic was first described with respect to asthma, but more recently an increased incidence of other allergic diseases, and of atrophy itself, has been identified. Numerous theories have been put forward to explain this epidemic, ranging from misadventures with symptomatically effective superficial therapies to a diminished incidence of protective infections in early childhood.

The former is thought to have led to an increase in allergic diseases because of the use of drugs that merely cover up chronic inflammatory conditions, and the latter has been attributed to a failure of the developing immune system to receive the signals needed for a protective immune response.