During exercise, the body's demand for oxygen increases and the production of carbon dioxide also rises. To meet these changing demands, the efficiency of gas exchange in the lungs must increase. Exercise enhances the efficiency of gas exchange in several ways. Firstly, it increases the rate and depth of breathing (ventilation), which ensures a more significant movement of air into and out of the lungs, providing a fresh supply of oxygen and removing carbon dioxide more effectively. Secondly, exercise leads to an increase in cardiac output, which means more blood is pumped through the pulmonary capillaries. This increased blood flow enhances the removal of carbon dioxide and uptake of oxygen. Moreover, regular exercise can improve the strength and efficiency of the respiratory muscles, like the diaphragm and intercostal muscles, making the process of ventilation more effective. In the long term, exercise can also increase the capillary density around the alveoli, providing a greater surface area for gas exchange.

Surfactant plays a crucial role in the lungs, primarily by reducing surface tension at the air-liquid interface within the alveoli. This reduction in surface tension has several important implications for gas exchange. Firstly, it prevents the collapse of alveoli at the end of expiration. Without surfactant, the alveoli would tend to collapse due to the high surface tension of the watery lining, particularly when lung volumes are low. By preventing alveolar collapse, surfactant ensures that a sufficient surface area is always available for gas exchange. Secondly, surfactant contributes to the compliance (flexibility) of the lungs, making them easier to inflate. This is particularly important during the process of breathing in, as it reduces the effort required to expand the lungs. Additionally, surfactant helps in maintaining the stability of the alveoli, ensuring that they are of similar sizes, which is important for uniform gas exchange. A lack of surfactant, as seen in conditions like neonatal respiratory distress syndrome, leads to alveolar collapse, decreased lung compliance, and severely impaired gas exchange.

The presence of moisture in the alveoli is crucial for efficient gas exchange. This moisture, in the form of a thin layer of fluid lining the alveoli, serves several vital functions. Firstly, it allows oxygen to dissolve, facilitating its diffusion across the alveolar membrane into the blood. Gases diffuse more readily in a liquid as compared to a dry surface, enhancing the rate of gas exchange. Additionally, the moisture helps in maintaining the structure of the alveoli. It prevents the alveolar walls from sticking together, which would otherwise lead to the collapse of the alveoli (a condition known as atelectasis) and significantly reduce the surface area available for gas exchange. Moisture also aids in the removal of foreign particles and pathogens, as it traps them and allows them to be removed from the respiratory system, maintaining the efficiency and health of the gas exchange surfaces.

Smoking adversely affects the characteristics of gas exchange surfaces in multiple ways. Firstly, it damages the alveoli, leading to a condition known as emphysema. In emphysema, the walls of the alveoli are destroyed, reducing the surface area available for gas exchange. This significantly impairs the lung's ability to oxygenate blood and remove carbon dioxide. Furthermore, smoking causes the thickening and narrowing of airways and swelling of lung tissue, which further hampers the efficiency of gas exchange. It also affects the blood supply to the alveolar surfaces. The presence of harmful substances in cigarette smoke leads to the inflammation and narrowing of blood vessels, which reduces blood flow to the alveoli. Reduced blood flow implies a decreased efficiency in oxygen pickup and carbon dioxide removal. Additionally, the action of smoking impairs the movement of the cilia in the respiratory tract, affecting the ability of the lungs to clear mucus and other debris. This can lead to a decreased efficiency in ventilation, further impacting gas exchange.

Environmental pollution can have detrimental effects on the gas exchange surfaces. Pollutants like particulate matter, ozone, nitrogen oxides, and sulfur dioxide can cause inflammation and damage to the alveoli and airways. This leads to conditions such as chronic bronchitis and emphysema, which impair the lung's ability to function efficiently. The damage caused by these pollutants can lead to a reduction in the surface area of the alveoli, thickening of the alveolar walls, and destruction of the capillary beds surrounding the alveoli. All these changes reduce the efficiency of gas exchange by increasing the diffusion distance and decreasing the area available for gas exchange. Additionally, pollutants can impair the body's immune response, leading to increased susceptibility to respiratory infections. These infections can further damage the gas exchange surfaces, creating a vicious cycle of reduced lung function and increased vulnerability to further harm.