The respiratory system processes oxygen using the lungs and airways, the smallest functional unit being the alveoli. The primary functions of the respiratory system are air conduction, air filtration, and gas exchange (Ross 664). These functions are sometimes disrupted by disorders of the respiratory system, including asthma. Asthma is characterized by chronic cough, wheezing, chest tightness, and shortness of breath, but some people may not experience these symptoms. Asthma is diagnosed through a physical exam, a lung function test called spirometry, chest X-rays, an allergy test, and a bronchoprovocation test to measure sensitivity to various common triggers (“What is asthma?”). Internally, people with asthma experience a trigger that causes inflammation and swelling of the airways, which can lead to an asthma attack (“Learn more about asthma”). Common triggers include cold air, allergens, irritants, sulfites, medications, respiratory infections, and physical activity (What is asthma?). The etiology of asthma is not fully understood, but the main factors that appear to play a role in the development of asthma are genetics, allergies, respiratory infections, and the environment. If a child's parents have asthma, the child is also likely to develop asthma. Some allergies are associated with asthma (“Learn more about asthma”). The risk of developing asthma increases if the child grows up in an environment where there are particles, such as cigarette smoke, in the air. Another risk factor is if the child gets respiratory infections when their immune system and lungs are not fully developed. Parasites, such as Dermatophagoides pteronyssinus or house dust mites, can also cause asthma. When the mite's feces are inhaled, the...... middle of paper...... European Respiratory Journal, July 2, 2001. Web. April 17, 2014. .Wadsworth, SJ, DD Sin, and DR Dorscheid. “Clinical update on the use of biomarkers of airway inflammation in the management of asthma.” National Center for Biotechnology Information. Dove Medical Press. US National Library of Medicine – Journal of Asthma and Allergy, June 30, 2011. 77-86. Print. April 16, 2014. .Warnick, Martha. “Tissue preparation”. Tissue preparation. University of California, San Francisco, May 18, 1997. Web. April 17, 2014. “What is asthma?” ". National Heart, Lung, and Blood Institute. U.S. Department of Health and Human Services, June 15, 2012. Web. April 16. 2014. .