Why is resistance lower in smaller vessels?

• A. Less airflow
• B. Increased total area
• C. Higher lung volume
• D. More elastic recoil

Answer: (B)

The choice stating that resistance is lower in smaller vessels due to increased total area is accurate because as the diameter of individual vessels decreases, the overall cross-sectional area of the network of smaller vessels increases significantly. In the circulatory and respiratory systems, when vessels split into smaller branches, each branch might have a smaller diameter, but there are many more of these smaller vessels compared to larger ones.

This increased total area allows for a greater volume of air or blood to flow through the network at any given time, which reduces the resistance the fluid encounters. In essence, while smaller vessels might have higher resistance individually due to their diameter, collectively, the vast number of these vessels ensures that the overall resistance to flow is lower. This principle is particularly important in understanding how blood and air can flow effectively through various parts of the body, facilitating better oxygen delivery and gas exchange.

The other options do not accurately address the relationship between vessel size, area, and resistance. For instance, less airflow would typically be a factor of resistance itself rather than a cause for lower resistance. Higher lung volume relates more to the capacity of the lungs rather than the resistance in the vessels. Similarly, more elastic recoil pertains to the lung's ability to expel air rather than directly affecting