Maximum surface area of circulating system is seen in

Options

A. (a) veins
B. (b) heart
C. (c) arterioles
D. (d) capillaries

Answer

To solve the question regarding which part of the circulatory system has the maximum surface area, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Options**:
- The options given are:
A. Veins
B. Heart
C. Arterios
D. Capillaries
- We need to evaluate each option to determine which has the maximum surface area.

2. **Analyzing Capillaries**:
- Capillaries are the smallest blood vessels in the body, with a diameter of only 5 to 10 microns.
- They form a dense meshwork throughout tissues, creating a complex network that significantly increases the surface area available for exchange.

3. **Function of Capillaries**:
- Capillaries are crucial for the exchange of materials between blood and tissues. They facilitate the transfer of gases (like oxygen and carbon dioxide), nutrients, and waste products.
- Their structure allows for a high surface area relative to volume, which is essential for efficient exchange processes.

4. **Comparing Other Options**:
- **Veins**: While veins do have a significant surface area, they are larger in diameter and do not have the same extensive network as capillaries.
- **Heart**: The heart is a muscular organ that pumps blood but does not have a large surface area for exchange.
- **Arterios**: This term likely refers to arteries, which are larger than capillaries and primarily function to carry blood away from the heart.

5. **Conclusion**:
- Based on the analysis, capillaries (Option D) have the maximum surface area in the circulatory system due to their extensive network and small size, allowing for efficient material exchange.

### Final Answer:
The maximum surface area of the circulating system is seen in **D. Capillaries**.