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,...