MEDICAL ANIMATION TRANSCRIPT: The lungs are part of the lower respiratory tract and contain a series of subdividing tubes, beginning with the bronchi. Air passes through the bronchi into smaller tubes called bronchioles then into tiny elastic sacs called alveoli, where gas exchange occurs. Pulmonary capillaries and alveoli share a thin membrane through which gas exchange occurs. Oxygen defuses from the alveoli into the blood for transport to body tissues, and carbon dioxide, a waste product of cellular processes diffuses from the blood into the alveoli to be exhaled from the body. Shifts in oxygen and carbon dioxide partial pressures in the blood can signal respiratory failure, a condition in which gas exchange is insufficient due to disease involving the lungs or other organs. In hypoxemic respiratory failure, too little oxygen defuses into the blood. In hypercapnic respiratory failure, too much carbon dioxide remains in the blood. Chronic obstructive pulmonary disease, known as COPD, and acute respiratory distress syndrome, known as ARDS, commonly result in respiratory failure. COPD includes two main conditions, chronic bronchitis and emphysema. Chronic bronchitis involves inflammation of the bronchial lining. Thick mucus accumulation along the bronchial lining and narrowing of the airways called bronchoconstriction which can result in blocked or narrowed airways. In emphysema, some alveolar walls are destroyed leading to fewer, larger, formless sacs. In addition, some of the bronchioles collapse impeding airflow out of the alveoli. In contrast, acute respiratory distress syndrome involves injury to one or both lungs caused by factors such as trauma or blood infection called sepsis. Inflammation leads to alveolar fluid accumulation and alveolar collapse reducing the surface area available for gas exchange. Common treatments for respiratory failure include oxygen therapy via supplemental oxygen or mechanical ventilation. Other common treatments include medications such as bronchodilators and steroids which reduce airflow resistance, and antibiotics which kill bacteria causing bronchitis and other infections.