Why do capillaries need to be thin-walled?

• A. To prevent the backflow of blood into the veins.
• B. To facilitate the rapid exchange of gases, nutrients, and waste products between blood and tissues.
• C. To withstand high blood pressure from the heart.
• D. To allow for the storage of large volumes of blood.

Answer: (B)

Verified step by step guidance

1. Understand the primary function of capillaries: Capillaries are the smallest blood vessels in the body and their main role is to facilitate the exchange of gases, nutrients, and waste products between the blood and surrounding tissues.
2. Consider the structure of capillaries: Capillaries have very thin walls, typically only one cell layer thick, which is crucial for their function.
3. Analyze why thin walls are important: The thin walls of capillaries allow for efficient diffusion of oxygen, carbon dioxide, nutrients, and waste products. This is because the shorter the distance these substances have to travel, the faster and more efficiently they can be exchanged.
4. Evaluate the options given: The options include preventing backflow, withstanding high pressure, and storing blood. Consider which of these functions align with the structure and primary role of capillaries.
5. Conclude with the correct reasoning: The thin walls of capillaries are essential for their role in the rapid exchange of substances, which is why the correct answer is to facilitate the rapid exchange of gases, nutrients, and waste products between blood and tissues.