Final answer:
Emphysema is a chronic lung disease characterized by the enlargement and stretching of the alveoli, leading to loss of elasticity and the inability to exhale completely.
Step-by-step explanation:
Emphysema is a chronic lung disease where the walls of the alveoli, the tiny air sacs in the lungs, break down. This leads to enlargement or stretching of the alveoli, causing a loss of elasticity and reduced capacity to exhale completely. It is an irreversible and debilitating condition commonly caused by smoking. In emphysema, there is a decrease in the surface area available for gas exchange, making it difficult for oxygen and carbon dioxide to be exchanged efficiently.