Unilateral leg redness, swelling, warmth, and pain may indicate which of the following?

A. Lung damage caused by COPD is reversible is incorrect because COPD involves chronic, progressive destruction of the airways and alveoli, particularly in emphysema and chronic bronchitis. While medications and interventions can manage symptoms and slow progression, the structural lung damage is irreversible.

B. COPD refers only to chronic bronchitis is incorrect because COPD is a broad term that encompasses multiple chronic lung conditions, primarily chronic bronchitis and emphysema. Some patients may have features of both, and less commonly, COPD can be influenced by alpha-1 antitrypsin deficiency.

C. COPD affects only those of European descent is incorrect because COPD affects individuals worldwide regardless of ethnicity. While certain genetic factors (e.g., alpha-1 antitrypsin deficiency) are more prevalent in some populations, the disease is not limited to European descent.

D. Smoking is the primary cause of COPD is correct because long-term cigarette smoking is the leading risk factor. Tobacco smoke causes chronic airway inflammation, mucus hypersecretion, ciliary dysfunction, and destruction of alveolar walls, leading to airflow limitation, impaired gas exchange, and progressive respiratory symptoms. Other contributing factors include environmental exposures (pollution, occupational dust), recurrent respiratory infections, and genetic susceptibility.

A. Larynx is incorrect because the larynx functions mainly as a passageway for air between the pharynx and trachea and houses the vocal cords. It does not participate in gas exchange.

B. Trachea is incorrect because the trachea serves as a conduit for air to move to the bronchi and lungs. Its rigid cartilage rings keep the airway open, but it does not have structures for oxygen and carbon dioxide diffusion.

C. Alveoli is correct because alveoli are tiny, thin-walled sacs at the end of the bronchioles where oxygen diffuses from inhaled air into the blood and carbon dioxide diffuses from the blood into the alveoli to be exhaled. The alveolar walls are extremely thin and surrounded by a dense network of capillaries, maximizing surface area for efficient gas exchange, which is the primary function of the respiratory system.

D. Bronchi is incorrect because the bronchi are larger airways that conduct air into each lung and then divide into smaller bronchioles. While they transport air deeper into the lungs, gas exchange does not occur in the bronchi.