Which of the following is a disease of the respiratory system?

Chronic obstructive pulmonary disease (COPD) is a significant respiratory condition that primarily affects the lungs and airways. It encompasses progressive lung diseases such as emphysema and chronic bronchitis. Individuals with COPD experience difficulty breathing due to airflow obstruction, often caused by long-term exposure to irritating gases or particulate matter, most commonly from smoking. The progressive nature of COPD leads to decreased lung function, making it harder for individuals to engage in daily activities.

In contrast, arthritis is a joint disease affecting the musculoskeletal system, not the respiratory system. Kidney stones are a renal issue related to the urinary system, involving the formation of small, painful mineral deposits in the kidneys. Brittle bone disease, or osteoporosis, is a condition that affects bone density and structure, which falls under the category of skeletal system diseases, rather than the respiratory system. Thus, COPD is the only option listed that directly pertains to diseases of the respiratory system.