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Health Effects of Asbestos Exposure

Asbestos is a term that refers to a group of naturally occurring fibrous minerals. Because of their resistance to decay and their remarkable insulating properties, asbestos fibers have been incorporated into thousands of products and materials. Unfortunately, it is now clear that exposure to airborne asbestos fibers can cause disease. The risk of developing asbestos-related disease varies according to the intensity, duration and nature of the exposure.

The Respiratory System

To be a significant health concern, asbestos fibers must be inhaled. An understanding of the mechanics of the respiratory system will aid in appreciating the potential for exposure and the resulting health effects.

Every cell in the body needs a constant supply of oxygen. The respiratory system meets this need by bringing oxygen to the bloodstream, which delivers it to each cell and carries away carbon dioxide. The lungs are the focal point of the respiratory system, which also includes the respiratory tract, the channel by which air flows into and out of the lungs. The drawing above is an illustration of the respiratory system. Inhaled air passes through the nose, where moisture and tiny hairs filter dust. It then passes down the throat where air is also humidified. Air continues into the trachea. Just above the heart, the trachea divides into two bronchi. Each bronchus leads into a lung where it subdivides into bronchioles and smaller air tubes - giving the appearance of an upside-down tree. The tiniest tubes end in globular air sacs called alveoli.

The actual exchange of gases - respiration - takes place in the alveoli. There, blood vessels only one cell thick allow oxygen and carbon dioxide to trade places. The carbon dioxide is exhaled back up the respiratory tract. The blood picks up fresh oxygen and transports it throughout the body.

 

The lungs, cone-shaped, balloon-like, elasticized tissue, are located on either side of the chest. Each lung is encased by a double layer of membrane, or pleura. One layer is attached to the lung, the other to the rib cage. Space and fluid between the two layers enable the lungs to expand and contract in the chest cavity without friction. When we breathe in, the diaphragm stretches out flat and muscles between the ribs contract with it, pulling the ribs up and out. This expands the chest cavity creating a vacuum between the linings that expands the lungs and sucks in air. When breathing out, the diaphragm and rib cage muscles relax, the ribs fall in and down, and the lungs contract and push out the carbon dioxide and unused oxygen.

The respiratory system is sensitive to bacteria, viruses, and many airborne particles that can be inhaled. Reactions to these irritants can disrupt the functioning of the system, resulting in many ailments including such things as: the common cold, hay fever, sinusitis, sore throat, acute or chronic bronchitis, emphysema, and lung cancer.

Natural Filters. The body has several mechanisms by which it filters the air it breathes. The tiny hairs in the nose filter out dust and airborne particles. Like the nose, the trachea and the bronchi are lined with small fine "hairs" called cilia. Together with mucous secreted by cells lining the airways, cilia trap particles and help prevent respiratory infections. the cilia beat in an upward direction sweeping foreign particles up to the back of the mouth where they are expelled or swallowed. Viruses and bacteria are also attacked by enzymes called lysozymes in the mucous cells. Microbes that slip through are usually handled by white blood cells called phagocytes that envolop and eat these invaders in the lung.

Cigarette smoking temporarily paralyzes the cilia. If smoking continues long enough, the cilia wither and die. They are never replaced. The efficiency of the cilia is replaced by the smoker's inefficient cough which attempts to rid the respiratory tract of foreign particles and excess mucus.

Dirty, contaminated air presents the greatest challenge to the respiratory system. Some of the particles entering the airways reach the alveoli. When this occurs, white blood cells called macrophages attempt to engulf and digest the particles. In the case of asbestos, we are dealing with a mineral fiber, as a substance which macrophages can often not successfully attack. As a means of secondary defense, the macrophages deposit a coating on the fibers which are then deposited in the smaller passages. Here they clog and actually scar the tissues. The walls of the alveoli lose their elasticity and useful function in respiration.

 

Asbestos Related Diseases

Asbestos exposure can cause a number of disabling and fatal diseases. The principal rout of exposure is by inhalation through the nose and mouth. Asbestos, traditionally valued for it's indestructibility, is especially resistant to the internal defenses of the human body. Once lodged inside the lungs, most fibers will not break up or dissolve, and they cannot be neutralized or removed.

Asbestosis

Asbestosis is a disease which is characterized by pulmonary fibrosis, a progressive scarring of the lungs caused by the accumulation of asbestos fibers. Asbestosis is associated exclusively with chronic, occupational exposure. The build up of scar tissue interferes with oxygen uptake through the lungs and can lead to respiratory and heart failure. Often, asbestosis is a progressive disease, even in the absence of continued exposure. Symptoms include shortness of breath, cough, fatigue, and vague feelings of sickness. When the fibrosis worsens, shortness of breath occurs even at rest.

Pleural Plaques

Pleural plaques and pleural calcification are markers of exposure and may develop 10 to 20 years after initial exposure. Plaques are opaque patches visible on chest x-rays that consist of dense strands of connective tissue surrounded by cells. All commercial types of asbestos induce plaques. Plaques can occur even when fibrosis is absent and do not seem to reflect the severity of pulmonary disease.

Lung Cancer

Of all the diseases related to asbestos exposure, lung cancer has been responsible for over half of the excess deaths resulting from occupational exposure. Although tissues and cells react to the presence of asbestos immediately, detectable symptoms take years, or more often decades, to manifest themselves. Asbestos-induced lung cancer may not show up on x-rays for twenty years or more after the exposure began. This delay between exposure and onset is referred to as the "latency period". Even in cases of prolonged heavy exposure, abnormalities commonly appear on x-rays only after ten or more years following exposure.

Asbestos as a Co-Factor: Other substances appear to cooperate with asbestos to multiply the risk of lung cancer. Asbestos exposure in combination with cigarette smoking can multiply the risk of developing lung cancer as much as ninety times over the risk to a non-smoker with no history of exposure to asbestos.

Mesothelioma

Mesothelioma, a malignant nodular type cancer of the membranes which line the lung cavity, is another disease related to asbestos exposure. Malignant mesotheliomas of these membranes (the pleura and the peritoneum) are extremely rare in persons with no history of asbestos exposure, but may account for 10% to 18% of excess deaths in workers exposed to asbestos. Generally, a latency period of at least 25 to 30 years is required in order to observe mesotheliomas, and some victims have had a latency period of forty years since their initial exposure to asbestos. This form of cancer is incurable and is usually fatal within a year after diagnosis. Mesothelioma has been associated with short term, incidental exposure, but here is no evidence of a relationship between cigarette smoking and mesothelioma risk.

 
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