Final answer:
Decreased capillaries in the alveolar walls of the elderly lead to impaired gas exchange, causing an increased partial pressure of oxygen in the alveoli and contributing to V/Q mismatch and age-related lung conditions.
Step-by-step explanation:
As a person ages, the number of capillaries in alveolar walls decreases, leading to reduced surface area for gas exchange. This physiological change impacts the efficiency of gas exchange, specifically the transport of oxygen into the bloodstream and the removal of carbon dioxide from it. It can result in an increase in the partial pressure of oxygen in the affected alveolus due to the mismatch in ventilation and perfusion (V/Q mismatch). When alveoli are damaged or less ventilated, the body compensates by constricting the pulmonary arterioles serving these alveoli, which decreases blood flow to them and redirects it to better-ventilated alveoli. Conversely, pulmonary arterioles dilate when there is a high partial pressure of oxygen, increasing blood flow. These changes can lead to various problems associated with aging, such as reduced lung function and diseases like chronic obstructive pulmonary disease (COPD).