COPD is primarily associated with which bodily system?

Chronic Obstructive Pulmonary Disease (COPD) is primarily associated with the respiratory system because it is a group of lung diseases that cause airflow blockage and breathing-related issues. The principal conditions included under COPD are emphysema and chronic bronchitis, both of which directly impair lung function and gas exchange in the lungs.

In COPD, the airways in the lungs become inflamed and produce excess mucus, which leads to difficulty in respiration. By affecting the respiratory system, COPD severely impacts an individual's ability to breathe and oxygenate their blood, highlighting the crucial role of this system in the disease.

While there may be implications for the cardiovascular system due to the reduced oxygen levels and the strain on heart function in those with COPD, the condition itself is fundamentally a respiratory disorder. The endocrine and digestive systems are not directly related to the mechanisms or symptoms of COPD, further supporting the respiratory system as the correct answer.